Basement Wall Insulation | Done WRONG
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- เผยแพร่เมื่อ 26 พ.ย. 2024
- Learn about how standard basement wall insulation practices can lead to issues as well as how building best practices offer potential solutions.
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In Norway (where I live) the outside if the concrete would be insulated (min 1/3 the thickness of inside insulation). Inside the vapor barrier would be put inside the insulation, not up against the concrete wall. This stops warm moist air from the inside of the house entering the insulation so it can’t condense on inside the insulation or on the concrete as it never reaches there. The vapor barrier should be taped so it’s air tight.
Seems to work. We opened a below ground wall in our 50 year old house recently and all was dry and in good condition.
Most excellent! The exterior insulation can work as well. European construction has embraced building science much longer than the United States! Thanks for sharing!
What I've learned through LOTS of research is that, especially in older homes with no outside vapor barrier, you basically need to seal the habitable basement space from the unfinished space. I almost visualize a finished basement as being a giant bowl extending from the first story down to the lower level. That way any moisture that does collect on the walls or floors can freely travel behind the foam board walls and sub floor down to the floor drain or through the cavities at the top of the walls. Obviously this isn't going to be a solution for major water intrusion, but for normal moisture levels in a basement it seems to be just the right thing.
We actually find that conditioning a properly insulated finished or unfinished basement is the best approach to controlling humidity and indoor air quality as long as bulk moisture is managed to drain away and/or out of the building.
Good point. You want the insider concrete to be warm-hence not too much-or no insulation there best and most-or all insulation- on exterior.
Rockwool does not achieve what you suggest. It keeps the concrete closer to the outside temp and not inside temp, increasing the potential for condensation !!…if you can’t get a sealed interior insulation and code requires you to have insulation try wood fiber -it’s hygroscopic potential will help buffer humidity extremes-buy in nay case most homes need active dehimidicayion in basement to avoid mold.
Short version: Great info on rationale for hardboard install to avoid condensation on concrete. Someone should tell the code ppl and builder all this too one of these years.
Agreed completely!
Absolutely correct, building code has to change. Kinda makes you wonder.
Building code has changed, that's why we are no longer required to put the vapor barrier up against the concrete, which causes mold. Everything needs to breath, this guy is wrong.
You are correct in a sense - most building materials are more forgiving when they do not trap moisture between layers. Building assemblies must manage air, moisture vapor, and bulk water to perform optimally. We want our assemblies to be as airtight as possible while maintaining the ability to breathe. The ability to breathe is typically accomplished by having components that allow moisture vapor to move through them, not air. When warm, humid air hits the relative cold surface of the concrete, condensation can occur. This is why using polyethylene plastic film as a vapor barrier does not solve the condensation issue and functions to trap the moisture which can result in mold. With concrete walls, the best solution is to shift the surface temperature of the concrete wall by insulating it with air impermeable, and somewhat vapor open insulation. We want to stop the air, but let moisture vapor move so that building assemblies can dry.
My contractor did 2 things differently he used metal studs, zero wood, and left a 4” air gap between the studs and the concrete wall, so zero contact with insulation
The contact with insulation isn't the problem, its the relatively warm, moist air of the conditioned home when it migrates into the air gap and meets the relatively cool concrete wall where it hits dewpoint and condensation forms on the interior surface of the concrete wall. Bulk moisture = musty odor in the basement and possibility of mold/mildew growth.
I've taken out all the old insulation and drywall, along with some mold that had developed over 25 years. The framing is right up against the concrete wall. Can you recommend the best way to move forward without relocating the frame? Also In Alberta Canada so we got all types of weather.
It is likely developing condensation inside the ductwork and draining back when it reaches a level of water in the duct. Where are you located?
Hi Todd , I didn’t quite get your explanation how to increase concrete wall temperature with insulation, as the only way to increase it is to install insulation outside. Installing inside will make concrete wall inside surface even colder, thus resulting a higher chance of condensation if there will be no vapour barrier. Roxul is a permeable material and will not stop vapour getting thru
@@pavelm.7673 your increasing the surface temperature on the interior of the foundation wall. This can be done with exterior insulation or interior insulation. With interior insulation, the wall is no longer exposed to the interior air- only the continuous insulation, which has a higher surface temperature that does not result in condensation.
How about spray foam? In Canada (my province anyway) I’m pretty sure we’re supposed to use Vapor wrap between the drywall and framing/insulation??
I’m looking to gut my basement and inspect walls for cracks etc. if all looks well, I’d rather spray foam between the studs for an airtight seal and I assume better R value??
If that is your desire, I would use closed cell spray foam and install it on the basement walls between the basement wall and the framing. Any framing touching the concrete walls will be prone to develop condensation and potentially mold and rot.
So we use Extruded Polystyrene (XPS) insulation board against the concrete wall, then add the stud frame, do we then use fiberglass insulation as well? Or is it enough to just use the polystyrene board?
It depends on your location (climate zone) and code version. The adopted version of the energy conservation code will specify the level of foundation insulation required.
Where are you located?
Great video! I'm in a northern climate and had to pull off the drywall of my framed and finished 1970's basement. It's currently fibreglass bats with a poly vapour barrier on the drywall side. Seeing as I've got the drywall off already I'd like to replace all the old insulation that's pretty musty. Would spray foam be a good option to avoid removing the framing and redoing it?
Closed cell spray foam would do the trick, but stay way from open cell in that application. Make sure you fill the gap between the studs and the poured concrete wall as well. If there is not gap, remove the studs!
@@AddisonHomes Thanks!
It might depend upon what is on the other side of the poured concrete. If there is a vapor barrier and foam insulation, studs on concrete on the inside might be alright.
Exterior insulation might change the situation, but basements in this part of the country (including this one) do not include exterior insulation. An exterior vapor barrier or waterproofing doesn't change the scenario at all - the interior condensation is not coming through the wall, it results from the interior wall temperature being below dewpoint.
@@AddisonHomesyes but if the exterior insulation keeps your foundation wall dry, it do at hit point. NB also interior insulation even if sealed does not warm up our foundation wall, anymore than fiberglass bay does-you a depending on the foam board to form a vapor tight assembly much harder in practice than it sounds in theory .
I basically settled on rigid foam board against the concrete until I started thinking about flammability. Now I'm a bit hesitant about it again.
@@GeneralChangFromDanang you should be able to find products that meet the smoke and flame spread limits outlined in the building code.
I have a basement from the 80s that has 2x2 stud walls fastened right to the block with a 4mil poly barrier between the block and studs. I ripped the wood paneling off and everything is in great shape with zero sign of moisture. What is the best way to insulate without ripping out studs? Should in install 1.5” foam board between studs and caulk leaving a .25” air chamber between the drywall and foam board? Or would I be better off just installing no insulation the way it has been for years dealing with a slightly colder environment?
That’s fantastic! I personally would remove the studs, add continuous insulation, and install furring strips such as the 2x2s you removed on top of the foam for drywall nailers.
You could certainly install rigid insulation between the 2x2s which would be much better than air permeable insulation.
Thanks for the reply. IF you were to keep it as is, do you see any issue with installing foam board over the existing 4mil poly barrier? Or would you remove then add rigid foam board?
@@vanwyckcodya I see no problem installing the foam board over the poly.
@@AddisonHomeswhat about fiberglass over poly in situation like this?
Can you put the foam board and vapor barrier on the on the OUTSIDE? I am not a builder, but I am in the process of finishing my basement walls, and when these foundations are built, I just don't understand why it would not be commonplace to attach foam board with a plastic sheeting of some sort on the OUTSIDE of every basement built?
You can definitely insulate the exterior of the basement wall. This can keep the dewpoint temperature on the interior of the wall warm enough to avoid condensation potential if you use enough insulation on the outside of the wall and extend the insulation from top to bottom on the exterior of the basement wall. Waterproofing on the exterior is essential to prevent bulk water from migrating through the poured wall. Waterproofing will control bulk water and insulation (interior or exterior) can shift the wall temperature to minimize dewpoint potential on the inside surface of the wall to prevent condensation.
Thank you. If I insulate from the inside, would you recommend a foam board, such as a Owens Corning 4 ft. x 8 ft. with R-10? I am in climate zone 5. @@AddisonHomes
@@unds85 That may work but check your current code. The 2021 IECC (International Energy Conservation Code) requires R-15 for basement walls in Climate Zone 5 if using continuous insulation like foam board.
One reason why ICF foundations are great for basement applications. In most northern or heating climates, the vapour barrier is applied to the warm in winter side of the insulation. Typically this is between the drywall and insulation. If the exterior basement foundation is properly waterproofed, there should be zero issues with mold on concrete foundation walls.
The "magic" with ICF foundations is that the exterior and interior of the foundation is insulated, eliminating the dew point surface on the interior which is completely unrelated to waterproofing. We must be extremely careful when installing vapor barriers to ensure that do not trap moisture in our assemblies and always have drying potential. This is why vapor open air barriers are replacing the vapor closed barriers in cold-climate wall assemblies.
We have a home built in the early 70’s. We recently started to remodel the basement by removing the tongue and groove panels and drywall from the studded walls. The basement walls are painted cinder block. The builder studded the perimeter and packed styrofoam sheets against the block walls in between the studs, then packed fiberglass insulation against the styrofoam and covered the studded walls with plastic sheeting. Condensation started rotting the studs on the south wall which is particularly exposed to sunlight. Paint is peeling off the block walls in order areas of the basement. We normally don’t have water infiltration in the basement so I think that this is due to the previous builder/owner going ape insulating the basement. As of now all styrofoam and insulation is removed. I was going to remove the damaged paint and repaint. Any suggestions on how to proceed with remodeling in terms of insulation? Thanks!
The condensation and peeling paint is likely caused by the moisture drive through the block when the sun hits the exterior. My approach would be to install rigid insulation board against the block walls in the basement (minimum of 1" in the South and even more in colder climates), then frame walls on top of the insulation board and install drywall. No plastic sheeting which will allow any trapped moisture in the framed wall to dry to the interior.
@@AddisonHomes
Would you paint the block walls after cleaning them?
I am getting ready to finish an older unfinished basement. The interior basement walls are raw concrete. What are the best practices? Should I adhere rigid goal boards to the concrete walls prior to framing the interior walls? If so what thickness would be necessary? Wouldn’t there still be a gap between the rigid foam boards and concrete that could allow for condensation? Would a closed cell spray foam be a better option?
Where are you located? My approach would be rigid foam board on the interior of the concrete walls at least 1.5 - 2 inches thick. Then frame the walls on the interior of the ridgid foam board. There is a product called insofast that is a perfect insulation board for this project - might be worth checking out as it eliminates the need for studs I believe.
I'm wary of the Superior foundation walls because there's no footing. I'd have footings done and then cover it with their required gravel. What I'm going to do with my basement, because it's not flat walls, is once the wall framing is done with a gap between the framing and the foundation walls, I'm going to Tyvek behind the framing with the moisture barrier facing the foundation wall. Need to overlap that properly. Then seal the edges.
There is a footing in the bottom of the Superior Wall. The compacted stone base below the wall ensures the load is spread based on the soil bearing conditions beneath. Your approach to framing basement walls and then trying to install Tyvek behind them sounds difficult - and it will not stop condensation from occuring on the interior side of the Tyvek. The moisture in this type of approach is from condensation on the colder surface, not moisture coming through the wall that Tyvek would stop. Easiest way to ensure no condensation is to install foam board on the inside of the walls and frame against it.
@@AddisonHomes Yeah I can't do that because it's a stone foundation that was then concreted over. What I'm going to do now is use foam insulating panels. What I will do is frame it in such a way that the side facing the concrete will weep right into the interior sump pump french drain system. It'll be perfect!
What kind of basement wall insulation would you use in southern climate? The coldest basement temp has been 52 degrees and hottest has been 72.
1" XPS foam board would do the trick against the concrete wall with framing to the interior of it. The key is keeping warm, moist air from contacting the colder surface of the concrete, resulting in condensation - think cold drink on a warm, humid day - the glass sweats on the outside. Same principle of dewpoint - you don't want this to happen in your wall. The R-5 XPS foam board is plenty to keep the surface warm enough so that dewpoint will never be reached. You really don't need any more insulation than this - but check your local code -
So if you put a rockwool board against it, do you still need a gap, and then put more insulation? Or do you just use rockwool right up against the concrete?
@@Playlist4213 I think you could put the Rockwool against the foundation but recommend you consult the manufacturer’s recommendation.
I already installed my frame this way against the concrete. Was going to to install fiberglass insulation but this making me think twice. Is there anything I can do besides just ripping out my studs and starting over?
You'd have to do exterior foam insulation all the way down to the footing. Not sure how your home is set but it will be a minimum of 8ft trench around the entire exterior. Most building codes require any visible exterior foam be sealed with something like a stucco finish. Places like Menards sell it for special order. I'd imagine it will be a lot more work than redoing the studs though but you'll have a warmer basement in the winter
That's a tough one! The absolute best way would be to shift the wall out and slide some rigid foam behind the studs.
So nailing Rockwool board first to the foundation then the stud wall filled with more Rockwool will prevent condensation/mold?
I would recommend a continuous insulation that is also a vapor barrier or retarder and application with adhesive vs. metal fasteners such as nails or concrete anchors (these will transmit the colder wall temperatures which can result in condensation).
Are those studs placed directly onto concrete?
Yes typically but due to inconsistencies in the concrete wall and studs there are gaps. The gaps don't solve the issue with condensation in the cavity however.
How would I insulate before framing in a CMU wall basement?
I would use continuous insulation appropriate for the climate zone.
Great info!
When considering rockwool, what measures are you using to retard moisture with a low perm coating? Since rockwool itself is not a vapor barrier/retarder vs using continuous foam board/spray foam which is a vapor retarder at 2” or greater?
The most important element needed in this type of wall assembly is eliminating any surfaces that might be at dew point temperature resulting in condensation potential. This is best done with an air impermeable insulation on the interior surface of the concrete foundation wall such as foam board.
I have exterior foam board around my poured walls? Do I have to put it inside also? 1 year old house. Or is another option to build my walls off of the poured walls a few inches to leave a gap?
That's great. I would still install a gap between the interior concrete wall and the wood framed wall.
This assuming concrete is not porous,but it is. A vapor barrier will just provide a place for moisture to get locked into, and will erode the walls. This wall will have pitting and damage over time with a barrier.
This is assuming the concrete is properly waterproofed on the exterior and is not discussing moisture infiltration through the concrete.
I have a 1 year old poured walkout basement wall exposed on the outside without waterproofing or covered with siding. The builders installed 1.5in foam board on the wall. They did a lazy job around outlets that drop from the ceiling and are installed thru metal conduit. It always felt drafty in those areas so i decided to pull the foam board off and i can see large spots of condensation on the wall. This is an unfinished basement also. At this point is the foam board just not providing enough insulation and still allowing heated air to reach behind due to a draft? Is this even a problem that there is moisture? Can i reinstall foam board and try to seal it better to prevent moisture occurring? I don't plan on finishing the space so just looking for guidance on what to do about the moisture. Thanks
It could be one of two things:
1) moisture infiltrating through the un-waterproofed concrete wall or
2) warm moist air flowing in around the poorly sealed outlets and condensing on the colder concrete.
Depending on your climate zone, 1.5 inches may or may not be enough to prevent the condensation. Where are you located?
@@AddisonHomesI'm located in northeast Ohio. I've since discovered it's surface moisture on the wall. I removed the form boards and the wall dried out in a day. I did a test and put the boards back up without sealing them and leaving obvious ways for warm air to reach behind. I also did a plastic bag test and taped it to the wall on all sides then covered that with foam. When i removed the foam again after a few cold days I had surface moisture again, except under the sealed plastic.
I sent photos and surprisingly the builder offered to fix it and just finished it a few days ago. They made sure to run spray foam along the top and bottom of the panels and it looks significantly better than before. I'm guessing i won't see the issue again.
Thank you for the reply.
Can you put the foam board on the cellar ceiling??
You can - but not sure what the intended application would be?
Hi. Thanks for the video. Would a folmar250 or 150 rigid foam board be okay to put directly against the poured concrete? Then frame in front of it? Then put kraft faced insulation inside the cavities? Would putting the 250 or 150 directly against the wall not allow the wall to breathe? My house is a 1988 build and the basement floor has a 2.5 inch opening with rock in it all around the perimeter of the basement floor. Thanks for your time.
using 2 in foam insulation followed by batts placed within a wood or steel stud wall are common practice, when placing the foam board use the glob method which should allow the foam to be held away from the wall by at least 1/8 inch, for the floor I would be using a dimple mat, followed by at minimum of 1/2in foam 25psi or higher, followed by standard 23/32 flooring osb running perpendicular to the foam board layout. The only thing to note is to build the floor before the wall studs.
any thickness of rigid insulation right up against it will do the trick as a moisture barrier. any batt insulation used in the framing can then be unfaced
Yes it would be fine. The main purpose is to stop the interior surface from hitting dewpoint (the foam board raises the interior surface temperature) resulting in condensation. You don't need the kraft faced insulation, you can use unfaced batt insulation which will allow any moisture in the wall to dry to the inside. The exposed 2.5 inch opening sounds like an interior french drain that may have been added after construction. This could be a source of humidity in the basement.
How are you sure they aren’t going to spray those cavities with closed cell spray foam? Or Siga Majrex and Mineral wool?
Pretty sure! This is the typical construction approach in the Southeast
What about a block wall in my attached garage that I'm turning into a room? Can I use regular insulation?
I would install at least 1" R-5 foam board against the block wall and install furring strips or frame the wall on the interior of the foam board. This will prevent any interior air that may leak into the framed wall from hitting a dew point surface resulting in condensation. Hope this helps!
@@AddisonHomes thank you!
I live in the midwest and want to insulate my 1980's basement. Can I put foamboard then studwall and then faced insulation in the stud cavity and then drywall? I know this is a double vapor barrier but I am seeing conflicting information on this. Any help would be appreciated.
if there are not studs currently installed, use the foam board and then build your walls, which should be insulated since 2in foam board is not enough
Great question- the foam board against the foundation wall is a great approach. Be sure to use what the energy code recommends for your climate zone. In a colder climate, more is better. You really don't need to use paper faced insulation with this approach since the foam board will nearly eliminate the dew point potential in the assembly. With unfaced cavity insulation, the assembly can then dry to the inside if needed.
@@AddisonHomes If there is a possibility of moisture coming through the basement walls is it advisable to glue foam board directly to the concrete walls? Wouldn't this trap moisture against the inside of the concrete walls potentially cause deterioration of the concrete? Appreciate any light you can shed on this. TIA.
Hey what do you think about gluing roofing paper or other contact barriers to the foundation wall and then adding batt insulation. Would this prevent any moisture issues or is foam board the only way to go since it has thermal properties.
Unfortunately, anything with no insulation properties will still result in likely condensation on that interior poured wall surface - just on the surface of the roofing paper or other material which will still result in the unfortunate potential for mildew and mold growth in the wall cavity.
No House wrap first frame/insulate with Roxul/poly/drywall simple
Wood framing with rockwool cavity insulation against a poured concrete wall with poly then drywall on the interior is only a matter of time before mold growth begins.
@@AddisonHomes Read what I said House Wrap first then frame then insulate then Polly then drywall this works simple 🙂
@@thegrantdanielsband good luck with that!
@@AddisonHomes Good luck with that? Of course you need to put the house wrap on the right way!! I have been doing this for years with block or concrete walls and never a mold problem and it is a simple problem solved very effectively 🙂
How are they doing it the “other way” that is generally minimum code? Batten with vapor barrier on the inside (not against the concrete wall) and taped not stapled?
The common approach that we see in the Southeast is paper faced fiberglass batt insulation, stapled to the inside of the stud, not even to the face.
@@AddisonHomes thank you sir. I’m in Metro ATL and curious as i’m trying to finish my basement and worried out our heat and humidity we have down here.
@@bwrick21 Definitely worth trying to do it the best way possible. We are in Greenville, SC so same conditions you have in ATL. A safe bet would be to install 1" foam board on the interior face of the poured walls, then you can install the framed wall against the foam. No cavity insulation would be needed in this case, but you can always add it if you desire. You'll likely notice that your basement is typically cooler than the upper levels of the home which is due to the constant ground temperature of around 60 degrees. This is a great benefit in the Summer, as little cooling is required, but will require some additional heating in the winter to bring it up from ground temp.
@@AddisonHomes thank your sir. Go tigers!
@@bwrick21 Go Tigers!
Very correct Re fiberglass, but very incorrect Re rockwool- it’s highly vapor permeable. You need rigid foam whether closed cell sprayed on or glued to wall.
Yes of course any insulation you can blow through will be vapor permeable. The foam board insulation raises the interior surface temp to reduce the chances for condensation.
What about blown in insulation
While better than batt insulation, blown in is not an air barrier, so still risks warm air from inside the home migrating to the cold basement wall and condensing.
Wouldn't an interior vapor barrier prevent the warm moist air from coming in contact with the cool concrete? There is nothing wrong with that method of insulating.
In theory, if it was completely air tight. However, in this approach, any moisture trapped in the wall cavity has no way to dry.
Continuous insulation against the concrete is the only sure fire way to prevent issues and allow drying to the interior.
@@AddisonHomes Sounds good but why doesn't building code mandate it? They had one job...
@@mckylecfc I always point out that building code is the MINIMUM legal standard for building. It doesn't necessarily embrace the best practices of building science as there are many constituents who influence the code process. The code essentially keeps our buildings from killing us quickly - no comment on long term health......
@@michelleusher2355 😬 well that's comforting...thanks for the great work, keep it up and hopefully the constituents start listening too..
@@mckylecfc great question. Remember, building code is the MINIMUM legal standard for building!
All concrete walls are done wrong. they all need hot tar on the exterior weeks after poured.
Not true actually! There are many different types of waterproofing, most better than hot tar, and there are many different grades of concrete - some that will not allow water to pass!
Builders are still, doing it the wrong way I am helping someone tear out their basement to fix the mess it ook 12 years to ruin this house living space with that smell
I can imagine! The knowledge is available for all builders - we just need to spread the word!
Nothing wrong with that way. Your way is preferred, though.
We would disagree with the way this wall is being constructed. Based on the laws of thermodynamics and building science, this wall will more than likely have issues in the future.
What? Wouldn't you just put the moisture barrier on the warm side of the studs like usual? Like you say the warmer air will move towards the colder air, so all good.
The problem is the lack of air tightness with an open stud wall against a concrete or masonry basement wall with air permeable insulation. The lack of air tightness in this wall assembly allows air to move through the assembly and potentially reach a dewpoint surface. In the moisture barrier scenario, this dewpoint surface could still occur at the basement wall surface due to air movement through the wall. Dewpoint could also occur at the moisture barrier, resulting in mold and mildew. Where the warmer air meets a cold surface below dewpoint, condensation occurs.
Agree completely. Its about condensation potential within the wall.