I've been in architecture for almost forty years and have automatically been putting a vapor barrier in behind the drywall because "that's how it's done". This was such an eye opening video. I don't know how may more projects I will be lucky enough to do, but my projects in Houston will certainly be done more correctly than they've been done in the past. I learn something from every single one of Matt's videos.
I have been in residential construction for 47 years and I find your videos very informative. I thought I had all the information necessary for building houses but your videos have showed me that all that information was based on the codes and recommendations from the old school. Thank you for showing me there is always something new and information to learn in this fastening industry. I am 72 years old and getting ready to self contract our retirement home in the panhandle of Florida. This video will help me with important decisions. Thank you.
Dave, Its this attitude that I wish I could find in the North Ga Mtns where I live. Builders always say this is the way my daddy did it etc. Good for you for not being to old to use your brain and speak out. We are never to old to learn.
Thanks Matt, I have been following your videos for about a year and really enjoy what you are sharing. It is a real pleasure to watch the younger guys like yourself focus on doing a high quality job. I am retired and don't build much in more. I make furniture for fun.
I liked this, and it will help a lot of people; the regional guidebooks are excellent. I live in the interior of British Columbia, and I can see +40 celsius in the summer, and -40 celsius in the winter. When it's cold outside, and you're cooking, breathing, showering, it is essential that there is an interior vapour barrier on homes in our neck of the woods. We have an AC unit too, and in a hot summer, that can introduce its own set of problems. I'm thinking that a good portion of Canadians absolutely need what your neighbours in Colorado, Minnesota, Wisconsin and North Dakota need.
Thank you very much! I'm building a house, using Rockwool and couldn't find a good answer to the question of interior poly. I put it on and got condensation on the south wall. I'm going to remove all of it now before I sheetrock. Also, don't paint the exterior a dark color. The heat gain is tremendous in a hot climate. I used a dark brown color and I'm repainting it now. Never thought about it, just liked the look. Oh well, pale yellow will be good too.
Love this! As an insulation contractor we often get asked to put up vapor barriers in homes, and I see it on drawings all the time. I have now made a policy to first try and educate the builder / Architect that is making the recommendation, and then refuse to bid the project unless it is changed.
Oh you read my mind, I have been researching this issue for weeks. Living in Virginia, remodeling a garage into a family room and running Roxul and the question of membrane/barrier is confusing, thank you very much for answering this question. You have helped me so much. As a homeowner/remodeler I have yet to find contractors who's knowledge goes beyond minimal requirements. Thank YOU!
Anne Chovey yes, I’m a relatively clever person, but never specialized in building. I’ve met too many blokes who are nice and have ‘hung out a shingle’ but can’t make convincing logic based arguments to justify why they chose a particular course of action and components for their assemblies. Worst part is when they hear a question they don’t understand they just get blustery and rude instead of being self-confident enough to say ‘I don’t know let’s find out’ really feel like there are more and more TH-cam channels like this that allow us all to grow together. Thanks again Matt for being so generous, funny and logical.
Matt, from a LEARNING (aka teaching) perspective, I think you produce some of the best videos anywhere. Explaining reference materials, including real examples, discussing conversationally. Keep it up!
thanks for helping us with concerns on our homes. I'm in the business of knowledge but i'm blowing away with so much more you can learn to protect your home. God bless matt. thanks again
loved this format! awesome to see pictures and examples while you’re talking about it. i live at the bottom of zone 4. my parents had an addition done in ‘92. had to tear out some drywall on the south side of the house which gets a lot of sun. a plastic barrier was behind it. the pink insulation was covered in mold at about 5% of the 4x8 space. it only affected the area that was a closet with a louvre door.
What I get out of this is that you should try to have slight negative pressure in your house during the winter and slight positive pressure during air conditioned periods. That way, anywhere there's an air leak it will be cool (dryer) air which will be able to absorb and carry away moisture as it moves into a warmer part of the wall, floor, or roof.
I built some house for a bigger chain style log home company they insisted on plastic over the insulation. In Michigan where I'm from we tried telling the gc it was a horrible idea and explained to him the exact points you brought up. Great information and video. Thanks for all the knowledge and new techniques you share.
Thanks for the explanation. Living in Australia 🇦🇺 I struggled to understand the difference between all the different types of barriers used and when you should use them. Some on the inside some on the outside, some in use both inside and outside in some areas. When you add closed cell foam into the mix too it’s just confusing. You wouldn’t believe the relaxed “standard” used down here. I’m living in a house (one I’m sure that was built by first year apprentices) it has only a single single brick wall with a 25- 50 mm air gap to a 2x4 wall frame with gyprock (Sheetrock). Yep no wall insulation at all. And this property was built in 2005. In the roof cavity I have 10 mm gyprock and corrugated iron (tin roofing). That’s in. There’s now a standard to adhere to which requires us to build stud walls with R1.5 batts. I’m not sure of the required R value in the ceiling cavity but what ever it is, it’s very relaxed. I built an investment home in 2002 and I asked the builder to use anticon under the roofing iron together with R3.6 batts on the ceiling. My builder told me I was just waisting my money with the anitcon. (Anticon is a anti condescending insulation. It’s a quite thick foil type material with fibreglass insulation attached to it, R1.5) to purchase it in large roles. As an electrician I loved working in this ceiling cavity, others without the under iron insulation were crazy hot, you could only work in that space for a limited time as it was so hot. But my property was was warm but not overwhelmingly hot. I can’t understand why we don’t try to better insulate our home’s. Thanks for the great content. Cam.
Thanks for sharing Cameron. We're looking to buy our first Aus home, coming from the UK the lack of insulation here is shocking. We're basically resigned to the idea of needing to install insulation in whatever we buy. Did you find any good Aus specific resources regarding vapour barriers? The wide temperature variation here made us think we'll need it on both sides. Cheers
Thank you for taking the time to explain this logically. Building inspectors simply parrot what someone told them and never check the science behind what they prescribe. I once had a building inspector tell me that my new patio needed to be able to remain standing if the house fell down. I asked him to explain to me under what circumstances he could envision my my house falling down and not the patio with it, and he just stared at me and then finally said, "well, that's what they told me we needed to look for."
That's insane. So many building inspectors just follow what they were told (as you already stated) or got it from a manual, but don't fundamentally understand any of the science behind the "why". Or, and the worst, is a perpetuated myth in building science that gets passed from inspector to inspector that becomes the norm, when it was never based on fact.
Thanks so much... I'm an old house carpenter in New England who has had multiple disagreements with building inspectors on this topic . Keep up the good work!
30 year builder here ,, thousands of units,, I will tell you exactly what poly on the inside of a house will do,, (in most of the USA)it will rot and or mold and mildew your walls and ext sheathing, rot your studs if wood ,, rust your framing if metal, soak your insulation if fiberglass , especially at bottom of walls effectively making fiberglass batts or any insulation virtually useless when damp.(( mineral wool and closed cell foam excluded)) . We figured that out in the late eighties,. Had many of discussion with unknowing bldg inspectors,, but I always won. But it was always a battle. Best to build a house with the major share of insulation rigid in two or more overlapping layers on exterior,, on top of a water/ air barrier ,, then clad exterior with whatever as long as there is a sufficient drainage plane between cladding and insulation,.. but still place mineral wool inside stud cavities , but i like at least a R 20 or so in exterior overlapping foam,, ((This method I KNOW works most everywhere .. AND DONT PUNCH HOLES IN YOUR WALLS ,,lol ceilings either for that matter . Air sealing from inside is key to thermal performance ,, do not need three dimensional airflow inside wall cavities or ceiling cavities .
Nate, if you were called to finish a basement, and the existing construction did not have the 2 layer of rigid isolation on the exterior, how would you go about framing the basement walls in regards to insulation and vapor barrier. This is for the new england area.
Great coverage of an important topic. I've been building an 8x12ft RV and following your vlogs and have found them valuable for everything from wall construction, window openings and of course moisture control including vapour barriers. I've found that a lot of what goes into home construction can be applied to RV construction. I've also found that a lot of ready made RV's don't do a lot when it comes to vapour control. My RV's walls are made with 2x3 wood studs with plywood sheathing covered in Soprema Sopraseal Stick VP. Walls are insulated with Rockwool insulation and the decision was made to forgo the vapour barrier completely knowing that RV's especially can become really humid really fast. Thanks for detailed content and real world examples in all of your videos.
I too am here wondering what to do with my van build. I live in hot humid south but plan to go north west…but don’t really plan to do long-term in snow climates.
Good one Matt . . . From across the pond . What you have just described is exactly what I have understood for some time now . It amazes me just how many Builders & in particular , Building Inspectors over here just don't seem able to grasp this concept . A bit of physics and common sense goes a long way . . . Great information & videos . . . . Keep them coming & thanks .
Matt, love this video, and I absolutely encourage you to do more like it. Maybe even a monthly video formatted like this called Nerding Out With Risinger and talk solely about a building science concept. What do you think about Lstiburek’s idea about a vapor retarder over your water control layer but behind your vented cladding. That way any condensation can gather on your water control layer and safely drain out. Hope I’m not misquoting him!
Great video! It is something I've come to suspect in recent years. It's nice to know that someone more experienced than I am has come to the same conclusion.
Thanks Matt. Might be worth mentioning the article “how to kill an old house” for those of us renovating homes. My PNW vintage craftsman was redone years ago and every wall I open has pink stuff in plastic from that reno, all beginning to turn black. Removing as I go. Short of removing all the historic cedar siding to insulate the envelope ala green building or perfect wall, I don’t think I have found any good choices for insulating walls of an historic house. None seems the consensus; that’s a hard pill to swallow in a hundred year old house. I’ve used some rockwool and bo barrier, in hopes it will hold up better over the next 20 years and make the house a bit more comfortable.
He’s got another video where they insulated a 100 yr old house in Texas. They use something called Delta Dry to create a cavity next the siding so it can breathe. Then they put a weatherproof sheet over that, THEN insulation goes in. I did it on my old house.That might work for ya!
Matt, you forgot to mention that the driving force moving moisture through a wall is vapor pressure. Why else would moisture move? Secondly, temperature differential is what drives heat through the wall. One can calculate for a wall composite, given inside and outside temperatures, what the temperature gradient is in the wall and if condensation could occur. I have seen a PTAC placed such in a building that it was blowing fully saturated 55F air on drywall. While the room side of the drywall looked fine, guess what was on the other side? The blackest mold you have ever seen. The learning is to never have HVAC vents directed against a wall. Lastly, I have seen in hotels where a conditioned guest room (cold) over an ambient work room created mold on the ceiling of the unconditioned and vented work room. The room above made the concrete floor slab so cold, moisture was condensing on the ceiling of the work room. As a mechanical engineer, I need to find the scientific root cause why there is a problem or what the solution should be. Just using a general chart for certain areas is not always the best method. Using science and physics will always give the correct answer.
Awesome video, very simple and clear. I'm from central/south Texas where it's mostly a dry heat and when "cold" it's dry cold however we do have the occasional humidity and being that im building my first mobile home and am already so invested money and time wise I want it to be as perfect as I can get it so videos like this and the other videos you make have helped me make decision on things that would have rendered me helpless otherwise. thank you sir I'm so thankful for people who share basic information like this that make such a huge impact
Great format! I used to be a home inspector in Michigan, and building my own house in Norway, #jarleifhouse, sure is different from the houses I inspected in Michigan. Balanced ventilation is required on new construction over here, as is a vapor barrier, as the houses are pressure tested prior to finalization and COO. The only exception; Log homes. Keep the great content coming! :)
Awesome video. I live outside of Montgomery Alabama. Building a barndomiun. Finally got my answer on vapor barriers. Going to add a ventilation system for fresh air. Lists of people here haven’t figured out the hvac with a tight house
Matt , I like the format that you used I like the way you showed it it was easy to understand not a lot of unnecessary information in there got to the point I’m a do it yourself or 70 year old guy who still working and got some major construction going on my house I’ve been referring to for last year almost 2 years for a lot of my updated what I feel necessities to repair what was wrong with my 17 year old house thanks buddy I think you do an awesome job
OMG, this was perfect! I was looking for a book that could help me with the Hot/Humid climate here in Florida and voila, you mention it! Thank you so much!
Hey Matt, I'm a new homeowner and I've jumped into the deep end of home remodeling by buying a 100+ year old house. It's a beautiful house with a cream city brick exteior around a stick frame style home. I have been looking far and wide for information on how to add insulation drywall to replace the crumbling lathe and plaster and currently insulation-less walls. Thank you for all the information in your videos. I have found them very informative and helpful in choosing materials and style of remodeling.
This was better than most of your other videos. We just need clear cut information with enough education on terminology to get done what we need to get done. Half the battle is people don't explain what context, and this did just that.
How did your project turn out? What method did you go with? I find the more digging you do in vapor barriers/insulation, the more questions come to light. Who's right and what's right for my situation.
@@chrisalister2297 Project went great! We live in a mild climate and code requires that we use, at minimum, a vapor barrier primer paint on the drywall which is the preferred method in our area and probably most cost effective. I’ll let you know If it is the right choice in 30+ years if we ever remodel and find damage or mold. There is,....what is right....what is required by code....and what is done. I can’t answer any of that for your situation. Good luck.
So no plastic sheeting on my wall but what about closed cell? I’m planning on spraying my walls with closed cell but won’t that be adding a vapor barrier?
Question for Matt & everyone, but first big kudos to Matt for all of these videos! I learn at the very least SOMEthing EVERY time I watch! Very sorry for the length, but… Scenario: I’ve got a fairly new build, attached garage that I want to heat for winter & eventually mini-split. Just enough heat to make it livable - not t-shirt heat. Builder specifically told me garage is UNinsulated - but drywall taped & mudded. 24” centers. Heat pump electric water heater in garage, so comparatively dehumidified interior. Pacific NW. Plan: After insulating garage door; I want to take down drywall from uninsulated walls & put in Rockwool batts, close walls with PVC slot wall Gladiator Gearwall, pretty much floor to ceiling, that I was generously gifted (read free). Maybe furring strips? Questions: Considering my building zone (4); marginal heat pump dehumidification; Rockwool instead of fiberglass; at least R15 maybe R23?; considering cold exterior & around 50 degree heated interior; with less breathable PVC walls… Do I bother to “vent” walls with slight opening around bottom & slight opening around top? If not, since Rockwool batts & PVC walls, no need for 6mil vapor barrier? Been researching all this, but some crisscrossing info & answers. Thanks a lot for taking the time; wordy, I know.
I am in building zone 7 , Winnipeg Canada, All houses her have poly vapor barriers. I remember our old house that had no barrier and the humidity would go in the attic and freeze on the underside of the roof and in the spring time huge chunks of ice could be heard falling and banging on the ceiling , wetting all the insulation in the attic and ruining it. Since all houses have basements , there is usually no problem with ground rain water seeping in from the bottom. So all the houses are up a couple of feet above grade. I put my sofa up against the outside wall and the sofa had a straight back. it was -35 outside and I have R30 walls. so I pulled the sofa away from the wall to vacuum and there was Ice on the wall. The Insulation in the sofa up against the wall brought the freezing point to the inside of the house and the humid air froze on the wall. That is when I realized how important the vapor barrier was.
@@rsmith02 As far as I know the Tyvek and other brands of air barriers are designed to allow water vapor to pass through so it doesn't get trapped in the middle of the wall. You still need a vapor barrier inside the house walls. If it is an old house with no vapor barrier , you can use oil based enamel paint on the walls and ceilings and that works. If you live in a hot climate then you need the vapor barrier on the outside of the house to stop humid air from entering the walls and condensing in the middle of the walls to which could form mold. That happens when you have A/C making the inside air colder than the outside.
Thank you, Matt. Allison Bailes' article "You Don’t Need a Vapor Barrier (Probably)" basically states that a vapor barrier is not needed, except under slabs and in crawl spaces. He states that the most effect way to keep moisture from the wall interior is to air seal holes in the walls.
Crazy humid in Central Florida for about 7 months a year. I had a “over “ wrapped wall that couldn’t breathe and it couldn’t release trapped water as a vapor. Major rotting occurred. It’s not so much water getting into the wall here or there (it’s going to get in somewhere) question is, can it get out? It needs a way out on the less humid side.
One of the most useful construction videos I've come across. There is very little consolidated and clear information on best practices available to us amateurs, so this is welcome education, much like many of your videos. Thanks! P.S.: Intro/extro music is way too loud. I watch at home after the kids go home. If I turn it up enough to hear your voice clearly, the intro music will wake up everyone in the house. Otherwise, great stuff!
The answer in my research is “no vapor barriers” for your steel building but an air barrier usually in the form of closed cell foam spray or sheet works best.
Great videos from here and RR. I think it all depends on location but I am not an expert which is why I am here. We just completed the dry in of a large pole barn structure. We are about to begin finishing the interior which will have both conditioned and unconditioned space. We have metal exterior siding over top of general house wrap. We will then bat insulate the interior and cover the walls with drywall. We have been told not to put up any plastic. We are located in northern South Carolina where summers are hot a humidity seems to be year round. I look forward to hearing the reply from Matt.
Depends on your climate. The vapour barrier should go on the warm side if the in/out temperature delta will allow condensation to occur. I live in the north and our typical wall assembly inside out is drywall - furring (allow some air movement to dry out any vapour that diffuses) - vapour barrier (p-e or closed styrofoam panels that will have less than 1 perm) - insulation in the wall cavity - open styrofoam panels( high perm to allow moisture to escape) glued on the back of your sheating - air barrier (tyvek or similar) - furring for air movement to dry any moisture - siding.
Thanks for a 'laser clarity moment' on this topic. Cuts right through the gibberish and gets to the point. I really like the format of this presentation over your flashy intros on the your other topics (not to get perspicuity).
You point out that in the colder zones that the sheet rock slows down the movement of moisture through the walls and that is enough except in zone 7. But then you point out that air leakage through cracks, crevices or holes in the sheet rock can allow seriously damaging amounts of water through the walls. In my opinion, this is exactly why you need a vapor barrier that can flex and stretch and cover cracks due to settlement and a barrier that can be sealed around electrical boxes such as receptacles switches land lights etc. such that a little movement won't rupture the barrier. As the house ages and some home owners drive nails and screws into the sheet rock to mount artwork, these holes are penetrations through the surface and interior of the sheet rock that allow air to flow through. in modern times many people are using humidifiers to maintain a comfortable and healthy humidity in their home in the heating seasons in the north. You can build a theoretical case to allow you to say that under perfect and new conditions, you don't need a vapor barrier; but but with the practicalities of a home as it ages, why not put in the added protection? Of course you can do a lot with flexible caulking to seal around boxes and you still may need that at the boxes when you use a membrane type barrier; but a tough, flexible membrane will be there during most typical structural movements caused by settle-ling or holes made by the home owner. As you pointed out, one thing you do not want is a hole in the wall that allows the warm humid air to continuously flow out through the wall and form condensation in the colder side of the wall; that is big trouble.
Thanks, Matt. This video outlines just one of the things I didn't know when we built our first house, but I'm certainly glad I saw this video while we're still in the planning for our next (and hopefully our last) house.
Thanks for the well organized info. Here in northern Canada a interior vapour barrier (6 mil poly) has been the standard for decades. There is conflicting information when building more efficient systems such as staggered stud or a continuous rigid foam outside of traditional framing. My current home is fairly well built with 2x6 walls with batt insulation, osb sheathing, a house wrap, and siding with a well sealed 6 mil poly under the drywall. Once the temp falls into the -20 F or colder our furnace(and most furnaces) has a built in humidifier which must be turned on to work with air management systems( VanE) I think the vapour barrier is more of an air barrier. Planning on building a much more efficient home with the r12 zip sheathing over 2x8 studs and raised heel trusses. We are trying to figure out the vapour barrier system as there have been local issues with very efficient homes developing moisture issues within the wall systems. I’ve watched quite a few of your videos and find them to be unbiased towards any one system and still very helpful. Thanks for the excellent content.
Most houses I’ve done established a vapor barrier using the paint on drywall. But I’m doing a cabin now with a plywood interior (so no paint). We’re in climate zone 4 and had planned to use plastic behind the plywood but after watching, it seems like the plastic would just encourage mold on the back of the ply. Right?
I realized that interior vapor barriers were bad when I was 15 or so. We found all kinds of mold on my dads remodel jobs. I’ve taken drywall down before and seen water droplets on the backside of the plastic...very bad. Have been against them ever since. Atleast in my climate zone. Great video.
I have a 140 year old fieldstone foundation in my basement. I had a lot of mold when I bought the house. It's been remediated and I'm installing a perimeter drain system/French drain and a dehumidifier. I'm likely not going to put sheet rock on the walls so that the foundation can breathe. I'm getting conflicting info about whether or not I should put a vapor barrier on the uneven stone walls. I'm also being told by some to use drylock paint or something like that. I'd love to have a finished basement but I think even with all of the work I'm doing there will always be some moisture coming from outside and below. I'm in NJ which means cold winter's and hot summers. Thank you
I'm doing a wood floor over a slab that doesn't have a vapor barrier under it. This is in the basement of an old house. I put down one of the new dimpled plastic barriers made for just such an application. I'm wondering if they will really help, or if you have had any experience with this sort of thing. Maybe a subject for another video?
august, Yes, I agree there is always moisture. I put down two layers of 1/2" osb glued and stapled together over the barrier. Didn't really have the ceiling height for sleepers.
Tom, I have the same type of house, 1870's and 6' 6'' ceiling. I still think you did all you could other than doing the first layer with pressure treated but there are issues with that so...
Watched flooring company do following. 6mil plastic on slab, tape seams properly, pressure treated 2x sleepers on layout of choosing (16 o/c or 24) ply then flooring
I love that u address building strategies vary greatly in different parts of the country !! So many DIY channels dont say where they are located. They are only telling people 1 way to do a project and that may not be the best way given location of viewer...
Very helpful video! Nice to see the discussion consider a broad range of potential circumstances. I think the format of this video works fine (i.e. using screen shots rather than needing to be at a job site).
Hey Matt I’m currently building a new construction home and after watching some of your videos and others I decided to air seal and insulate my home myself. I have a vaulted great room area and I didn’t want to have to try and walk on that to blow cellulose and a local surplus store listed some R49 unfaced batts for 30$ a bag so I snagged some up for that portion of my attic. I live in climate zone 4 in central KY. If my ceiling is properly air sealed will the unfaced batts be okay?
Great video!! Thanks for the info. Very helpful! Really liked the format too. The articles and diagrams were very helpful. Enjoy all your vids and the resources you site.
I've worked on a few basements in what would be zone 8, except Canada uses different zone numbers. (Go to Fargo, and keep going.) I think Matt is correct about air barriers being more important than vapour barriers. The main problem I see with fibreglass insulation in basements is the sometimes extreme difference in temperature between the footings and the top of the foundation. (Currently about 50 degrees Celsius/ 90 degrees Fahrenheit right next to me.) If you don't have an obsessively tight seal everywhere, this will pull air in at the top of the wall, cool it, and force it out at the bottom. I've been in a lot of houses where you can feel cold air being pushed out of unsealed electrical outlets. In a couple of cases, we had to use heat guns to melt ice that was holding the old insulation solid to the top of the foundation wall. I believe rockwool stops this vertical air movement better than fibreglass, but not as well as Tuck Taping the heck out of every possible opening. Foam insulation works a lot better in basements, but the only area it's really worth the money on a DIY job is in bathrooms.
Get yourself some rigid polystyrene insulation. There’s a lot of options out there. Preferable one with a thermal barrier on the inside. The polystyrene, when installed correctly, will act as a vapor/air barrier in a basement without absorbing the collected moisture. Still, if you end up finishing, drywall and wood studs are a bad idea. You’ll never stop water from coming into the basement. Galvanized steel studs and one of the many cement board brands are the way to go. If your not finishing the basement, remember to never store things in cardboard and get yourself a good, energy star rated dehumidifier. P.S. do not put an exhaust in a basement. I’ve seen some contractors and waterproofed who put those in. All you end up doing is creating a vacuum for more wet air to fill the space. It’s a never ending battle.
Thanks so much for clarifying that about the plastic on the inside of the home. Don't do it in Dallas. I'm renovating an old 1920's shiplap house - exterior wood siding and shiplap is installed directly on the wall studs ....no insulation of course. In the locations where we were replacing rotted wood siding on the exterior, we added tar paper before installing new wood siding. On the inside where we had to remove some shiplap for wiring and windows, we put tar paper between the studs, anticipating insulation would be placed over it. Some areas will not have any tar paper unless I remove all the shiplap on the walls to do so. My questions: 1. Is the tar paper fine to use before I use batt insulation in the open wall cavities? 2. What about the wall cavities that I did not open up and have no tar paper in them (the shiplap walls)? Just blowing in insulation in the shiplap walls without any vapor barrier - is that ok? 3. Crawl Space - We are keeping the original wood floors, but of course a subfloor was not used in those days, so the wood floor is installed directly to the joists and is exposed to the outside temperatures in the crawl space. What is best for this scenerio? The floors are going to be cold for sure in the winter. What is the best thing to do in this case? Should we install the plastic vapor or air barrier? Some say spray foam insulation, but that could be more costly for a rental.
In Canada it is recommended to have a vapour barrier with insulation 2/3 on outside and 1/3 inside. Rim joists or concrete should have R10 rigid insulation on outside to prevent cold from being transferred through the structure.
I’ve always wondered about this having moved to various states and seeing it in use and not in use. My thoughts have always been that a vapor barrier is also synonymous with a moisture trap! Aside from an exterior wrap like Tyvek under siding to keep out high humidity and in general to limit airflow inward, I just never thought the opposite inside the wall was necessary too. As the saying goes, too much of anything can be a bad thing. I could only see that moisture trapped between plastic and drywall in hot southern states would eventually turn into mold if that moisture cannot escape. On some level a wall system needs to be able to breathe.
Like the format, however use either bigger fonts in your browser or lower resolution for your monitor. This will produce more readable screen shots and will require less zooming.
Loved the video - there seems to be a lot of nonsense regarding vapour barriers - I love the comment "the reason you might want to install one is to keep the building inspector happy". Living in cold n wet UK. I've regularly lined the coldd face of interior summer house walks with thick damp course plastic, packed with insulation then merrily clad. Some of them have been up for decades now and not a hint of a problem even when they have had hot tubs installed! I personally think adequate ventilation is the key and my humble plastic sheet functions as a wind barrier which combined with the packed loft roll limits air flow!
I have pulled many walls apart over the years. Plastic on the inside is a bad idea. That guy Holmes on tv loves it, what a joke. Up here in NY old school tar paper lasts 40 years and looks like new under the siding. Original Tyvek becomes like string from the acids in cedar. If you want a super tight house closed cell foam sprayed would be my choice with 30lb tar paper over plywood. To tight of a house isn’t as good as it sounds. You will have to ad make up air after the fact.
daversj Tar paper is Ole School. Tyvac is just to keep the inspector happy. Use Zip, Delta or one of the liquor applied. Mat is in to excellence and building science, building home to last centuries, not Twenty years!
I like felt i.e. tar paper for the outside it breaths VS some house wraps that do not breath. Fact I was talked into using high tek roofing underlayment instead of felt, the roofing decking buckled in spots from moisture.
In Holmes defense, he is in Canada which is where Matt is saying you need a moisture barrier. Perhaps not plastic but that is the older school thinking of course.
Agree. I just pulled plastic down an hour after putting it up. Western NY, 90 degree day stapled 6mil plastic after Roxul. It started building moisture immediately. Glad I didn't put drywall up yet. Thank you for this video.
...and the debate rages on! As an architect, people in our industry beat this topic to death about where, when and what type or vapor barriers to use. Problem is we don't know the weak points or flaws until a building is renovated or torn down many years down the road.
Zone 6 would be the same weather as Alberta and Saskatchewan, and vapour barriers are used 100%. Dont see how a line on a map changes the weather where it "might be" used
The answer has to be less because millions of homes have been built using a vapor barrier. If a vapor barrier caused this much mold, mildew, you would be seeing it everywhere, yes ? Not saying which way is right but...
abacab87: Precisely. The vapor barrier has been doing its job - trapping moisture that would otherwise leak into the structure and potentially cause mold. In cold climates, you want these between your insulation and drywall. Unless the home has significant air leaks or moisture issues, the vapor will be trapped on the outside (cold side) of the poly, protecting the interior of the structure including the air you breathe.
This is somewhat dangerous advice to be giving without enforcing how important air sealing is. The 30 pint scenario is very realistic given the way most houses are not sealed at the drywall level, or the weather barrier level on the outside for that matter. Air sealing is critical, and traditionally it’s done with a plastic sheet in the inside and a housewrap on the outside. Changing that requires a lot of planning ahead and communication between the builder and trades.
Plastic sheet does little to nothing for air sealing. You have holes all over due to things like staples and you have big outlet holes that are rarely if ever sealed around the outlet or at the back wire penetrations, possibly vents, small cracks between the joists and drywall that aren't sealed like at the floor, and my other things other things. The house wrap on the outside has little to nothing to do with air sealing either. Moisture at the surface they are covering, but not air and not the moisture that moves through those cracks and gaps.
Appreciate this video, Matt. Closing on a house in Chicago this week. Place needs insulation in the attic and this will help me decipher what my GC will say. Cheers.
Nice summary on hard and misunderstood subject. You just gained my respect. One could summarize, that it is not as bad if something gets wet, as long as it has chance to dry up. Any plastic has high likelyhood of hindering the drying.
Thanks. I’m from Pa and familiar with the buildings there but just moved to Mississippi and have a mini house I am construction that I was still on the fence about which side the vapor barrier should be on. I think after watching this I am just leaving it at house wrap because it is on the souther half of Ms and it has R45 walls and R60 roof so there shouldn’t be much if any cool air from inside condensing on the outside of the house.
Excellent video, thanks Matt. Lots of these 'way things are done' that often aren't the right way to do things that we need the science behind making the right decision. Super helpful.
Very informative video. I noticed the article mentioned an air barrier might be needed. What is the difference? Maybe you could link to another video on this topic.
I have been researching this for a few weeks and this man just solved all my problems in 8 minutes. Thank you!
Excellent format, including referencing published articles from knowledgeable sources.
I've been in architecture for almost forty years and have automatically been putting a vapor barrier in behind the drywall because "that's how it's done". This was such an eye opening video. I don't know how may more projects I will be lucky enough to do, but my projects in Houston will certainly be done more correctly than they've been done in the past. I learn something from every single one of Matt's videos.
I love this format. Short, to the point, but well backed up with resources and reason. Much appreciated.
Thanks Greg!
I have been in residential construction for 47 years and I find your videos very informative. I thought I had all the information necessary for building houses but your videos have showed me that all that information was based on the codes and recommendations from the old school. Thank you for showing me there is always something new and information to learn in this fastening industry. I am 72 years old and getting ready to self contract our retirement home in the panhandle of Florida. This video will help me with important decisions. Thank you.
Dave, Its this attitude that I wish I could find in the North Ga Mtns where I live. Builders always say this is the way my daddy did it etc. Good for you for not being to old to use your brain and speak out. We are never to old to learn.
Dave im 53 and I can only hope I still have your attitude when im your age. Stay young brother
Thanks Matt, I have been following your videos for about a year and really enjoy what you are sharing. It is a real pleasure to watch the younger guys like yourself focus on doing a high quality job. I am retired and don't build much in more. I make furniture for fun.
I liked this, and it will help a lot of people; the regional guidebooks are excellent. I live in the interior of British Columbia, and I can see +40 celsius in the summer, and -40 celsius in the winter. When it's cold outside, and you're cooking, breathing, showering, it is essential that there is an interior vapour barrier on homes in our neck of the woods. We have an AC unit too, and in a hot summer, that can introduce its own set of problems. I'm thinking that a good portion of Canadians absolutely need what your neighbours in Colorado, Minnesota, Wisconsin and North Dakota need.
What do you do in the summer? No sure how to cope with humidity coming one direction in summer and another in winter
Do you need a vapor barrier or just an air barrier that lets the building dry to either side depending on the season?
Thank you very much! I'm building a house, using Rockwool and couldn't find a good answer to the question of interior poly. I put it on and got condensation on the south wall. I'm going to remove all of it now before I sheetrock. Also, don't paint the exterior a dark color. The heat gain is tremendous in a hot climate. I used a dark brown color and I'm repainting it now. Never thought about it, just liked the look. Oh well, pale yellow will be good too.
Thank you! For helping with a do/don't plastic sheeting argument!!
Thanks for breaking it down into a simple format. Some of the use of language in most sites get confusing. Very helpful
Love this! As an insulation contractor we often get asked to put up vapor barriers in homes, and I see it on drawings all the time. I have now made a policy to first try and educate the builder / Architect that is making the recommendation, and then refuse to bid the project unless it is changed.
so just tyvex or tar paper on the outside only ? nothing on the inside?
Oh you read my mind, I have been researching this issue for weeks. Living in Virginia, remodeling a garage into a family room and running Roxul and the question of membrane/barrier is confusing, thank you very much for answering this question. You have helped me so much. As a homeowner/remodeler I have yet to find contractors who's knowledge goes beyond minimal requirements. Thank YOU!
Anne Chovey yes, I’m a relatively clever person, but never specialized in building. I’ve met too many blokes who are nice and have ‘hung out a shingle’ but can’t make convincing logic based arguments to justify why they chose a particular course of action and components for their assemblies. Worst part is when they hear a question they don’t understand they just get blustery and rude instead of being self-confident enough to say ‘I don’t know let’s find out’ really feel like there are more and more TH-cam channels like this that allow us all to grow together. Thanks again Matt for being so generous, funny and logical.
Matt, from a LEARNING (aka teaching) perspective, I think you produce some of the best videos anywhere. Explaining reference materials, including real examples, discussing conversationally. Keep it up!
thanks for helping us with concerns on our homes. I'm in the business of knowledge but i'm blowing away with so much more you can learn to protect your home.
God bless matt.
thanks again
loved this format! awesome to see pictures and examples while you’re talking about it. i live at the bottom of zone 4. my parents had an addition done in ‘92. had to tear out some drywall on the south side of the house which gets a lot of sun. a plastic barrier was behind it. the pink insulation was covered in mold at about 5% of the 4x8 space. it only affected the area that was a closet with a louvre door.
What I get out of this is that you should try to have slight negative pressure in your house during the winter and slight positive pressure during air conditioned periods. That way, anywhere there's an air leak it will be cool (dryer) air which will be able to absorb and carry away moisture as it moves into a warmer part of the wall, floor, or roof.
that is an inspiring thought
I built some house for a bigger chain style log home company they insisted on plastic over the insulation. In Michigan where I'm from we tried telling the gc it was a horrible idea and explained to him the exact points you brought up. Great information and video. Thanks for all the knowledge and new techniques you share.
Thanks for the explanation.
Living in Australia 🇦🇺 I struggled to understand the difference between all the different types of barriers used and when you should use them. Some on the inside some on the outside, some in use both inside and outside in some areas. When you add closed cell foam into the mix too it’s just confusing.
You wouldn’t believe the relaxed “standard” used down here. I’m living in a house (one I’m sure that was built by first year apprentices) it has only a single single brick wall with a 25- 50 mm air gap to a 2x4 wall frame with gyprock (Sheetrock). Yep no wall insulation at all. And this property was built in 2005.
In the roof cavity I have 10 mm gyprock and corrugated iron (tin roofing). That’s in.
There’s now a standard to adhere to which requires us to build stud walls with R1.5 batts. I’m not sure of the required R value in the ceiling cavity but what ever it is, it’s very relaxed.
I built an investment home in 2002 and I asked the builder to use anticon under the roofing iron together with R3.6 batts on the ceiling. My builder told me I was just waisting my money with the anitcon. (Anticon is a anti condescending insulation. It’s a quite thick foil type material with fibreglass insulation attached to it, R1.5) to purchase it in large roles.
As an electrician I loved working in this ceiling cavity, others without the under iron insulation were crazy hot, you could only work in that space for a limited time as it was so hot. But my property was was warm but not overwhelmingly hot.
I can’t understand why we don’t try to better insulate our home’s.
Thanks for the great content.
Cam.
Thanks for sharing Cameron. We're looking to buy our first Aus home, coming from the UK the lack of insulation here is shocking. We're basically resigned to the idea of needing to install insulation in whatever we buy. Did you find any good Aus specific resources regarding vapour barriers? The wide temperature variation here made us think we'll need it on both sides. Cheers
Thank you for taking the time to explain this logically. Building inspectors simply parrot what someone told them and never check the science behind what they prescribe. I once had a building inspector tell me that my new patio needed to be able to remain standing if the house fell down. I asked him to explain to me under what circumstances he could envision my my house falling down and not the patio with it, and he just stared at me and then finally said, "well, that's what they told me we needed to look for."
That's insane. So many building inspectors just follow what they were told (as you already stated) or got it from a manual, but don't fundamentally understand any of the science behind the "why". Or, and the worst, is a perpetuated myth in building science that gets passed from inspector to inspector that becomes the norm, when it was never based on fact.
Since I live in Wisconsin and going to insulate my garage I think I will use a plastic sheet for vapor barrier.
Thanks so much... I'm an old house carpenter in New England who has had multiple disagreements with building inspectors on this topic . Keep up the good work!
30 year builder here ,, thousands of units,, I will tell you exactly what poly on the inside of a house will do,, (in most of the USA)it will rot and or mold and mildew your walls and ext sheathing, rot your studs if wood ,, rust your framing if metal, soak your insulation if fiberglass , especially at bottom of walls effectively making fiberglass batts or any insulation virtually useless when damp.(( mineral wool and closed cell foam excluded)) . We figured that out in the late eighties,. Had many of discussion with unknowing bldg inspectors,, but I always won. But it was always a battle. Best to build a house with the major share of insulation rigid in two or more overlapping layers on exterior,, on top of a water/ air barrier ,, then clad exterior with whatever as long as there is a sufficient drainage plane between cladding and insulation,.. but still place mineral wool inside stud cavities , but i like at least a R 20 or so in exterior overlapping foam,, ((This method I KNOW works most everywhere .. AND DONT PUNCH HOLES IN YOUR WALLS ,,lol ceilings either for that matter . Air sealing from inside is key to thermal performance ,, do not need three dimensional airflow inside wall cavities or ceiling cavities .
BTW good video
Nate, if you were called to finish a basement, and the existing construction did not have the 2 layer of rigid isolation on the exterior, how would you go about framing the basement walls in regards to insulation and vapor barrier. This is for the new england area.
Nate. Same question about basement vapor barrier
Great coverage of an important topic. I've been building an 8x12ft RV and following your vlogs and have found them valuable for everything from wall construction, window openings and of course moisture control including vapour barriers. I've found that a lot of what goes into home construction can be applied to RV construction. I've also found that a lot of ready made RV's don't do a lot when it comes to vapour control. My RV's walls are made with 2x3 wood studs with plywood sheathing covered in Soprema Sopraseal Stick VP. Walls are insulated with Rockwool insulation and the decision was made to forgo the vapour barrier completely knowing that RV's especially can become really humid really fast. Thanks for detailed content and real world examples in all of your videos.
I too am here wondering what to do with my van build. I live in hot humid south but plan to go north west…but don’t really plan to do long-term in snow climates.
I'm a homeowner, thinking of building in northern Idaho, love all of your info, esp when you are "super geeky"
format was good. precicely what i was searching for. I keep coming back to your channel. you are killing it man!
Totally blew my mind. I've never heard this before. Thanks for the video and for the resources.
Good one Matt . . . From across the pond . What you have just described is exactly what I have understood for some time now . It amazes me just how many Builders & in particular , Building Inspectors over here just don't seem able to grasp this concept . A bit of physics and common sense goes a long way . . . Great information & videos . . . . Keep them coming & thanks .
Matt, love this video, and I absolutely encourage you to do more like it. Maybe even a monthly video formatted like this called Nerding Out With Risinger and talk solely about a building science concept. What do you think about Lstiburek’s idea about a vapor retarder over your water control layer but behind your vented cladding. That way any condensation can gather on your water control layer and safely drain out. Hope I’m not misquoting him!
This is an excellent idea!
Yep, love the format. Love learning the technicals.
loved this video as well
Great video! It is something I've come to suspect in recent years. It's nice to know that someone more experienced than I am has come to the same conclusion.
Thanks Matt. Might be worth mentioning the article “how to kill an old house” for those of us renovating homes. My PNW vintage craftsman was redone years ago and every wall I open has pink stuff in plastic from that reno, all beginning to turn black. Removing as I go. Short of removing all the historic cedar siding to insulate the envelope ala green building or perfect wall, I don’t think I have found any good choices for insulating walls of an historic house. None seems the consensus; that’s a hard pill to swallow in a hundred year old house. I’ve used some rockwool and bo barrier, in hopes it will hold up better over the next 20 years and make the house a bit more comfortable.
He’s got another video where they insulated a 100 yr old house in Texas. They use something called Delta Dry to create a cavity next the siding so it can breathe. Then they put a weatherproof sheet over that, THEN insulation goes in. I did it on my old house.That might work for ya!
So good to see you addressing this correctly. I fight with builders and the occasional inspector over this regularly. Building Science for the win.
Thanks very much. I've been planning a redo, but could never talk myself into installing a vapor barrier. It always seemed counterintuitive.
And now I just saved hundreds of dollars and time. THANKS for the tech talk!
Matt, you forgot to mention that the driving force moving moisture through a wall is vapor pressure. Why else would moisture move? Secondly, temperature differential is what drives heat through the wall. One can calculate for a wall composite, given inside and outside temperatures, what the temperature gradient is in the wall and if condensation could occur.
I have seen a PTAC placed such in a building that it was blowing fully saturated 55F air on drywall. While the room side of the drywall looked fine, guess what was on the other side? The blackest mold you have ever seen. The learning is to never have HVAC vents directed against a wall. Lastly, I have seen in hotels where a conditioned guest room (cold) over an ambient work room created mold on the ceiling of the unconditioned and vented work room. The room above made the concrete floor slab so cold, moisture was condensing on the ceiling of the work room.
As a mechanical engineer, I need to find the scientific root cause why there is a problem or what the solution should be. Just using a general chart for certain areas is not always the best method. Using science and physics will always give the correct answer.
Awesome video, very simple and clear. I'm from central/south Texas where it's mostly a dry heat and when "cold" it's dry cold however we do have the occasional humidity and being that im building my first mobile home and am already so invested money and time wise I want it to be as perfect as I can get it so videos like this and the other videos you make have helped me make decision on things that would have rendered me helpless otherwise. thank you sir I'm so thankful for people who share basic information like this that make such a huge impact
Great format! I used to be a home inspector in Michigan, and building my own house in Norway, #jarleifhouse, sure is different from the houses I inspected in Michigan. Balanced ventilation is required on new construction over here, as is a vapor barrier, as the houses are pressure tested prior to finalization and COO. The only exception; Log homes. Keep the great content coming! :)
Awesome video. I live outside of Montgomery Alabama. Building a barndomiun. Finally got my answer on vapor barriers. Going to add a ventilation system for fresh air. Lists of people here haven’t figured out the hvac with a tight house
This was the perfect video for me, I had a client ask about this yesterday. Thanks!
Matt , I like the format that you used I like the way you showed it it was easy to understand not a lot of unnecessary information in there got to the point I’m a do it yourself or 70 year old guy who still working and got some major construction going on my house I’ve been referring to for last year almost 2 years for a lot of my updated what I feel necessities to repair what was wrong with my 17 year old house thanks buddy I think you do an awesome job
OMG, this was perfect! I was looking for a book that could help me with the Hot/Humid climate here in Florida and voila, you mention it! Thank you so much!
Hey Matt, I'm a new homeowner and I've jumped into the deep end of home remodeling by buying a 100+ year old house. It's a beautiful house with a cream city brick exteior around a stick frame style home. I have been looking far and wide for information on how to add insulation drywall to replace the crumbling lathe and plaster and currently insulation-less walls. Thank you for all the information in your videos. I have found them very informative and helpful in choosing materials and style of remodeling.
Very cool! Thanks for watching. Best to you!
Thank you. You just saved me a full step in my remodel!!!
Your video is very helpful. Literally 100's of opinions on this topic. You sound clear and concise. I like the references.
Best content yet Matt!!! Thank you.
This was better than most of your other videos. We just need clear cut information with enough education on terminology to get done what we need to get done. Half the battle is people don't explain what context, and this did just that.
Getting ready to start the design process and this is the exact kind of video I’m looking for! Great stuff Matt!
How did your project turn out? What method did you go with? I find the more digging you do in vapor barriers/insulation, the more questions come to light. Who's right and what's right for my situation.
@@chrisalister2297 Project went great! We live in a mild climate and code requires that we use, at minimum, a vapor barrier primer paint on the drywall which is the preferred method in our area and probably most cost effective. I’ll let you know If it is the right choice in 30+ years if we ever remodel and find damage or mold. There is,....what is right....what is required by code....and what is done. I can’t answer any of that for your situation. Good luck.
Damn, how can every single video on this channel be so inspiring？
So no plastic sheeting on my wall but what about closed cell? I’m planning on spraying my walls with closed cell but won’t that be adding a vapor barrier?
Closed cell is a vapor barrier
Learned more in your videos in 30 min than all the DIY videos put together thanks!!
Love the format because the info was great! keep it up, thanks.
Question for Matt & everyone, but first big kudos to Matt for all of these videos! I learn at the very least SOMEthing EVERY time I watch!
Very sorry for the length, but…
Scenario:
I’ve got a fairly new build, attached garage that I want to heat for winter & eventually mini-split. Just enough heat to make it livable - not t-shirt heat. Builder specifically told me garage is UNinsulated - but drywall taped & mudded. 24” centers. Heat pump electric water heater in garage, so comparatively dehumidified interior. Pacific NW.
Plan:
After insulating garage door; I want to take down drywall from uninsulated walls & put in Rockwool batts, close walls with PVC slot wall Gladiator Gearwall, pretty much floor to ceiling, that I was generously gifted (read free). Maybe furring strips?
Questions:
Considering my building zone (4); marginal heat pump dehumidification; Rockwool instead of fiberglass; at least R15 maybe R23?; considering cold exterior & around 50 degree heated interior; with less breathable PVC walls…
Do I bother to “vent” walls with slight opening around bottom & slight opening around top? If not, since Rockwool batts & PVC walls, no need for 6mil vapor barrier?
Been researching all this, but some crisscrossing info & answers. Thanks a lot for taking the time; wordy, I know.
I am in building zone 7 , Winnipeg Canada, All houses her have poly vapor barriers. I remember our old house that had no barrier and the humidity would go in the attic and freeze on the underside of the roof and in the spring time huge chunks of ice could be heard falling and banging on the ceiling , wetting all the insulation in the attic and ruining it. Since all houses have basements , there is usually no problem with ground rain water seeping in from the bottom. So all the houses are up a couple of feet above grade.
I put my sofa up against the outside wall and the sofa had a straight back. it was -35 outside and I have R30 walls. so I pulled the sofa away from the wall to vacuum and there was Ice on the wall. The Insulation in the sofa up against the wall brought the freezing point to the inside of the house and the humid air froze on the wall. That is when I realized how important the vapor barrier was.
What if you had a tight air barrier but not a vapor barrier- would diffusion still be an issue?
@@rsmith02 As far as I know the Tyvek and other brands of air barriers are designed to allow water vapor to pass through so it doesn't get trapped in the middle of the wall. You still need a vapor barrier inside the house walls. If it is an old house with no vapor barrier , you can use oil based enamel paint on the walls and ceilings and that works. If you live in a hot climate then you need the vapor barrier on the outside of the house to stop humid air from entering the walls and condensing in the middle of the walls to which could form mold. That happens when you have A/C making the inside air colder than the outside.
Thank you, Matt. Allison Bailes' article "You Don’t Need a Vapor Barrier (Probably)" basically states that a vapor barrier is not needed, except under slabs and in crawl spaces. He states that the most effect way to keep moisture from the wall interior is to air seal holes in the walls.
Crazy humid in Central Florida for about 7 months a year. I had a “over “ wrapped wall that couldn’t breathe and it couldn’t release trapped water as a vapor.
Major rotting occurred.
It’s not so much water getting into the wall here or there (it’s going to get in somewhere) question is, can it get out?
It needs a way out on the less humid side.
I would think in HIGH humidity areas, spray foam would be your friend. That seals the wood and stops air flow all together.
One of the most useful construction videos I've come across. There is very little consolidated and clear information on best practices available to us amateurs, so this is welcome education, much like many of your videos. Thanks!
P.S.: Intro/extro music is way too loud. I watch at home after the kids go home. If I turn it up enough to hear your voice clearly, the intro music will wake up everyone in the house. Otherwise, great stuff!
So when building my post frame structures with metal siding and no plywood or osb sheeting... still no vapor barrier? Great video matt
The answer in my research is “no vapor barriers” for your steel building but an air barrier usually in the form of closed cell foam spray or sheet works best.
Also following both RR and Matt ... What's the answer for my new 40x60 heated post frame building?
I have the same question
Great videos from here and RR. I think it all depends on location but I am not an expert which is why I am here. We just completed the dry in of a large pole barn structure. We are about to begin finishing the interior which will have both conditioned and unconditioned space. We have metal exterior siding over top of general house wrap. We will then bat insulate the interior and cover the walls with drywall. We have been told not to put up any plastic. We are located in northern South Carolina where summers are hot a humidity seems to be year round. I look forward to hearing the reply from Matt.
Depends on your climate. The vapour barrier should go on the warm side if the in/out temperature delta will allow condensation to occur. I live in the north and our typical wall assembly inside out is drywall - furring (allow some air movement to dry out any vapour that diffuses) - vapour barrier (p-e or closed styrofoam panels that will have less than 1 perm) - insulation in the wall cavity - open styrofoam panels( high perm to allow moisture to escape) glued on the back of your sheating - air barrier (tyvek or similar) - furring for air movement to dry any moisture - siding.
Thanks for a 'laser clarity moment' on this topic. Cuts right through the gibberish and gets to the point. I really like the format of this presentation over your flashy intros on the your other topics (not to get perspicuity).
You point out that in the colder zones that the sheet rock slows down the movement of moisture through the walls and that is enough except in zone 7. But then you point out that air leakage through cracks, crevices or holes in the sheet rock can allow seriously damaging amounts of water through the walls. In my opinion, this is exactly why you need a vapor barrier that can flex and stretch and cover cracks due to settlement and a barrier that can be sealed around electrical boxes such as receptacles switches land lights etc. such that a little movement won't rupture the barrier. As the house ages and some home owners drive nails and screws into the sheet rock to mount artwork, these holes are penetrations through the surface and interior of the sheet rock that allow air to flow through. in modern times many people are using humidifiers to maintain a comfortable and healthy humidity in their home in the heating seasons in the north. You can build a theoretical case to allow you to say that under perfect and new conditions, you don't need a vapor barrier; but but with the practicalities of a home as it ages, why not put in the added protection? Of course you can do a lot with flexible caulking to seal around boxes and you still may need that at the boxes when you use a membrane type barrier; but a tough, flexible membrane will be there during most typical structural movements caused by settle-ling or holes made by the home owner. As you pointed out, one thing you do not want is a hole in the wall that allows the warm humid air to continuously flow out through the wall and form condensation in the colder side of the wall; that is big trouble.
Thanks, Matt. This video outlines just one of the things I didn't know when we built our first house, but I'm certainly glad I saw this video while we're still in the planning for our next (and hopefully our last) house.
Nice video buddy, & yeah the format was cool!
Thanks for the well organized info. Here in northern Canada a interior vapour barrier (6 mil poly) has been the standard for decades. There is conflicting information when building more efficient systems such as staggered stud or a continuous rigid foam outside of traditional framing.
My current home is fairly well built with 2x6 walls with batt insulation, osb sheathing, a house wrap, and siding with a well sealed 6 mil poly under the drywall. Once the temp falls into the -20 F or colder our furnace(and most furnaces) has a built in humidifier which must be turned on to work with air management systems( VanE) I think the vapour barrier is more of an air barrier.
Planning on building a much more efficient home with the r12 zip sheathing over 2x8 studs and raised heel trusses. We are trying to figure out the vapour barrier system as there have been local issues with very efficient homes developing moisture issues within the wall systems.
I’ve watched quite a few of your videos and find them to be unbiased towards any one system and still very helpful.
Thanks for the excellent content.
Most houses I’ve done established a vapor barrier using the paint on drywall. But I’m doing a cabin now with a plywood interior (so no paint). We’re in climate zone 4 and had planned to use plastic behind the plywood but after watching, it seems like the plastic would just encourage mold on the back of the ply. Right?
Yes. Use "Kitchen and Bath" paint in high moisture areas. I do wish more builders would use green board in bathrooms, too many do not.
I realized that interior vapor barriers were bad when I was 15 or so. We found all kinds of mold on my dads remodel jobs. I’ve taken drywall down before and seen water droplets on the backside of the plastic...very bad. Have been against them ever since. Atleast in my climate zone. Great video.
How about a video on how to make the walls breath the best? To let any moisture escape
Brent, that was the idea behind houses built in the early 20th century, they just didn't have the science to back it up. Laughing loudly.
I have a 140 year old fieldstone foundation in my basement. I had a lot of mold when I bought the house. It's been remediated and I'm installing a perimeter drain system/French drain and a dehumidifier. I'm likely not going to put sheet rock on the walls so that the foundation can breathe. I'm getting conflicting info about whether or not I should put a vapor barrier on the uneven stone walls. I'm also being told by some to use drylock paint or something like that. I'd love to have a finished basement but I think even with all of the work I'm doing there will always be some moisture coming from outside and below. I'm in NJ which means cold winter's and hot summers. Thank you
I'm doing a wood floor over a slab that doesn't have a vapor barrier under it. This is in the basement of an old house. I put down one of the new dimpled plastic barriers made for just such an application. I'm wondering if they will really help, or if you have had any experience with this sort of thing. Maybe a subject for another video?
Tom, I think you did right by putting the barrier down, especially over concrete which always will have moisture. Use pressure treated joists also.
august, Yes, I agree there is always moisture. I put down two layers of 1/2" osb glued and stapled together over the barrier. Didn't really have the ceiling height for sleepers.
Tom, I have the same type of house, 1870's and 6' 6'' ceiling. I still think you did all you could other than doing the first layer with pressure treated but there are issues with that so...
august, Yes, it's hard to know how far to take things. I know two layers of ply would have been a lot better than the osb. I guess time will tell.
Watched flooring company do following. 6mil plastic on slab, tape seams properly, pressure treated 2x sleepers on layout of choosing (16 o/c or 24) ply then flooring
I love that u address building strategies vary greatly in different parts of the country !! So many DIY channels dont say where they are located. They are only telling people 1 way to do a project and that may not be the best way given location of viewer...
Good job Matt, I've wondered about this subject. Keep it go'in.
Very helpful video! Nice to see the discussion consider a broad range of potential circumstances. I think the format of this video works fine (i.e. using screen shots rather than needing to be at a job site).
Hey Matt I’m currently building a new construction home and after watching some of your videos and others I decided to air seal and insulate my home myself. I have a vaulted great room area and I didn’t want to have to try and walk on that to blow cellulose and a local surplus store listed some R49 unfaced batts for 30$ a bag so I snagged some up for that portion of my attic. I live in climate zone 4 in central KY. If my ceiling is properly air sealed will the unfaced batts be okay?
I forgot to mention how great your info on poly barriers, great video for sure.
Big problem is actually the use of pink fibreglass insulation as it absorbs moisture and grows black mold. Roxul or isocyanate do not absorb moisture
Great video!! Thanks for the info. Very helpful! Really liked the format too. The articles and diagrams were very helpful. Enjoy all your vids and the resources you site.
What about a vapor barrier on walls in a basement in a zone 6?
shutterassault1 what is the verdict?
I've worked on a few basements in what would be zone 8, except Canada uses different zone numbers. (Go to Fargo, and keep going.) I think Matt is correct about air barriers being more important than vapour barriers. The main problem I see with fibreglass insulation in basements is the sometimes extreme difference in temperature between the footings and the top of the foundation. (Currently about 50 degrees Celsius/ 90 degrees Fahrenheit right next to me.) If you don't have an obsessively tight seal everywhere, this will pull air in at the top of the wall, cool it, and force it out at the bottom. I've been in a lot of houses where you can feel cold air being pushed out of unsealed electrical outlets. In a couple of cases, we had to use heat guns to melt ice that was holding the old insulation solid to the top of the foundation wall. I believe rockwool stops this vertical air movement better than fibreglass, but not as well as Tuck Taping the heck out of every possible opening. Foam insulation works a lot better in basements, but the only area it's really worth the money on a DIY job is in bathrooms.
Get yourself some rigid polystyrene insulation. There’s a lot of options out there. Preferable one with a thermal barrier on the inside. The polystyrene, when installed correctly, will act as a vapor/air barrier in a basement without absorbing the collected moisture. Still, if you end up finishing, drywall and wood studs are a bad idea. You’ll never stop water from coming into the basement. Galvanized steel studs and one of the many cement board brands are the way to go. If your not finishing the basement, remember to never store things in cardboard and get yourself a good, energy star rated dehumidifier.
P.S. do not put an exhaust in a basement. I’ve seen some contractors and waterproofed who put those in. All you end up doing is creating a vacuum for more wet air to fill the space. It’s a never ending battle.
Great video! Answered all my questions and didn’t focus on one specific zone. PERFECT!
Loved the reference material as well.
What about in basements?
Thanks so much for clarifying that about the plastic on the inside of the home. Don't do it in Dallas.
I'm renovating an old 1920's shiplap house - exterior wood siding and shiplap is installed directly on the wall studs ....no insulation of course. In the locations where we were replacing rotted wood siding on the exterior, we added tar paper before installing new wood siding. On the inside where we had to remove some shiplap for wiring and windows, we put tar paper between the studs, anticipating insulation would be placed over it. Some areas will not have any tar paper unless I remove all the shiplap on the walls to do so.
My questions:
1. Is the tar paper fine to use before I use batt insulation in the open wall cavities?
2. What about the wall cavities that I did not open up and have no tar paper in them (the shiplap walls)? Just blowing in insulation in the shiplap walls without any vapor barrier - is that ok?
3. Crawl Space - We are keeping the original wood floors, but of course a subfloor was not used in those days, so the wood floor is installed directly to the joists and is exposed to the outside temperatures in the crawl space. What is best for this scenerio? The floors are going to be cold for sure in the winter. What is the best thing to do in this case? Should we install the plastic vapor or air barrier? Some say spray foam insulation, but that could be more costly for a rental.
In Canada it is recommended to have a vapour barrier with insulation 2/3 on outside and 1/3 inside. Rim joists or concrete should have R10 rigid insulation on outside to prevent cold from being transferred through the structure.
Nice, Great format, trusted resources and most important Information anyone can Understand
Thanks Matt I love the geeky stuff!!
I’ve always wondered about this having moved to various states and seeing it in use and not in use. My thoughts have always been that a vapor barrier is also synonymous with a moisture trap! Aside from an exterior wrap like Tyvek under siding to keep out high humidity and in general to limit airflow inward, I just never thought the opposite inside the wall was necessary too. As the saying goes, too much of anything can be a bad thing.
I could only see that moisture trapped between plastic and drywall in hot southern states would eventually turn into mold if that moisture cannot escape. On some level a wall system needs to be able to breathe.
Like the format, however use either bigger fonts in your browser or lower resolution for your monitor. This will produce more readable screen shots and will require less zooming.
Loved the video - there seems to be a lot of nonsense regarding vapour barriers - I love the comment "the reason you might want to install one is to keep the building inspector happy". Living in cold n wet UK. I've regularly lined the coldd face of interior summer house walks with thick damp course plastic, packed with insulation then merrily clad. Some of them have been up for decades now and not a hint of a problem even when they have had hot tubs installed! I personally think adequate ventilation is the key and my humble plastic sheet functions as a wind barrier which combined with the packed loft roll limits air flow!
I have pulled many walls apart over the years. Plastic on the inside is a bad idea. That guy Holmes on tv loves it, what a joke. Up here in NY old school tar paper lasts 40 years and looks like new under the siding. Original Tyvek becomes like string from the acids in cedar. If you want a super tight house closed cell foam sprayed would be my choice with 30lb tar paper over plywood. To tight of a house isn’t as good as it sounds. You will have to ad make up air after the fact.
daversj
Tar paper is Ole School. Tyvac is just to keep the inspector happy. Use Zip, Delta or one of the liquor applied. Mat is in to excellence and building science, building home to last centuries, not Twenty years!
I like felt i.e. tar paper for the outside it breaths VS some house wraps that do not breath. Fact I was talked into using high tek roofing underlayment instead of felt, the roofing decking buckled in spots from moisture.
In Holmes defense, he is in Canada which is where Matt is saying you need a moisture barrier. Perhaps not plastic but that is the older school thinking of course.
Agree. I just pulled plastic down an hour after putting it up. Western NY, 90 degree day stapled 6mil plastic after Roxul. It started building moisture immediately. Glad I didn't put drywall up yet. Thank you for this video.
Good format and useful information. I encourage you to do more videos like this.
...and the debate rages on! As an architect, people in our industry beat this topic to death about where, when and what type or vapor barriers to use. Problem is we don't know the weak points or flaws until a building is renovated or torn down many years down the road.
Thanks, Matt, for putting a ton of great information into a short, easy to understand video!
In Canada, ALL THE TIME
Yes. But not in the US
how about seattle?
Zone 6 would be the same weather as Alberta and Saskatchewan, and vapour barriers are used 100%. Dont see how a line on a map changes the weather where it "might be" used
audex, You just need a good roof :P
how about a hrv
Greta topic. Thank you for pointing out the sources. I have more to read on a topic that's been debated around my circle in NY for a while.
Ok, so you don't *need* It, but if you want it, will it cause more problems than it solves?
The answer has to be less because millions of homes have been built using a vapor barrier. If a vapor barrier caused this much mold, mildew, you would be seeing it everywhere, yes ? Not saying which way is right but...
My father used it against the basement foundation so when the concrete weeps it doesn’t go to the insulation.
Probably yes. Read Martin Holladay's thoughts on the subject as pointed out in the video.
I rip houses apart everyday. I almost always see mold when a vapor barrier is used, and almost never when it is not used.
abacab87: Precisely. The vapor barrier has been doing its job - trapping moisture that would otherwise leak into the structure and potentially cause mold. In cold climates, you want these between your insulation and drywall. Unless the home has significant air leaks or moisture issues, the vapor will be trapped on the outside (cold side) of the poly, protecting the interior of the structure including the air you breathe.
Thanks Matt! Don’t forget us in Hawaii who love the build show too! Keep up the awesome job buddy! Aloha!
This is somewhat dangerous advice to be giving without enforcing how important air sealing is. The 30 pint scenario is very realistic given the way most houses are not sealed at the drywall level, or the weather barrier level on the outside for that matter.
Air sealing is critical, and traditionally it’s done with a plastic sheet in the inside and a housewrap on the outside. Changing that requires a lot of planning ahead and communication between the builder and trades.
Plastic sheet does little to nothing for air sealing. You have holes all over due to things like staples and you have big outlet holes that are rarely if ever sealed around the outlet or at the back wire penetrations, possibly vents, small cracks between the joists and drywall that aren't sealed like at the floor, and my other things other things. The house wrap on the outside has little to nothing to do with air sealing either. Moisture at the surface they are covering, but not air and not the moisture that moves through those cracks and gaps.
Appreciate this video, Matt. Closing on a house in Chicago this week. Place needs insulation in the attic and this will help me decipher what my GC will say. Cheers.
At 68 you just changed my paradigm. Will save me some work in the future if I build again. Thanks.
Nice summary on hard and misunderstood subject. You just gained my respect. One could summarize, that it is not as bad if something gets wet, as long as it has chance to dry up. Any plastic has high likelyhood of hindering the drying.
Matt Risinger is dam good. He knows his subject matter, and he's an inherently talented and skilled contractor.
Thank you for all the great ideas and the educational support you provide. Have a good day.
Thanks. I’m from Pa and familiar with the buildings there but just moved to Mississippi and have a mini house I am construction that I was still on the fence about which side the vapor barrier should be on. I think after watching this I am just leaving it at house wrap because it is on the souther half of Ms and it has R45 walls and R60 roof so there shouldn’t be much if any cool air from inside condensing on the outside of the house.
Excellent video, thanks Matt. Lots of these 'way things are done' that often aren't the right way to do things that we need the science behind making the right decision. Super helpful.
Thanks for the information........this is exactly what I needed to know.
Very informative video. I noticed the article mentioned an air barrier might be needed. What is the difference? Maybe you could link to another video on this topic.