Condensation/Sweating on garden office roof
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- เผยแพร่เมื่อ 6 ต.ค. 2024
- The condensation/sweating on this garden office roof is a problem I get asked about many times.
Condensation or sweating in lofts, cold roofs or unvented roofs is a big problem. When you are in the garden and you have construction moisture thrown into the equation you have an even a bigger problem!
Sweating on the underside of a flat metal roof is even more difficult to stop. Condensation through conductivity of the roofing material is really what we are talking about. If your roofing membrane is thick, and therefore insulates the topside of the roof, the problem of the roof sweating in the cold months of the year would not happen as much. Unfortunately, this is why we see so many GRP (fibre glass) roofs failing. So, to explain the problem - the underside of the roof covering is getting cold and the rising air containing moisture from the room below or from the air passing through the venting, condenses on the cold underside of the roofing deck. The water vapour in the warmer air hits the colder surface and changes from a gas to a liquid.
The environment around the base of the home office is also important to how the roof vents
Moisture from the environment around the garden room or office will rise and go through the vents of the cold roof. This moisture in the winter will be what condensates on the back of the roofing boards and the colder the roofing boards the more likely the sweating or condemnation will be. So the external environment of the home office or garden room is very important to how the roof works if it's a cold roof that is vented correctly. you should also make sure that the AVCL (air vapour control layer) is correctly installed above the plasterboard and under the insulation, in the roof, the AVCL (air vapour control layer) is extremely important in stopping moister from inside the cold roof of the office green from rising up into the vented space and adding to condensation that may be drawn in from the surrounding areas.
I will post the link to the author of the drawing below when I find out who it was as this is a very good diagram.
This viewer sent me photos of his sweating cold flat roof that hadn't been build incorrectly and was now sweating so much that water was dripping through into the room below. He hadn't fitted ventilation to between the joists and he hadn't added an AVCL (air vapour control layer) he had cut lights into the ceiling and air was pouring into the cavity. Mould on the timbers and on the back of the roof decking was starting to grow. So the question is "Can I save my sweating cold flat roof" Using information from some ware on the internet I took some research that shows that plasterboard has a good vaper resistance and the fact that the ceiling is airtight should solve the problem. airtightness in flat roofs is always the biggest problem I come across. People get all hung up about the vapour control layer and forget that more moisture gets into the roof through the movement of air than through a vapour barrier.
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Steven Dickinson
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I’m a builder, I bought my property in wales two years ago, the large garage, 7.5mx7.5m has a metal roof, the rafters run perpendicular to run of the metal roofing sheets, I was having horrendous sweating on mine, water was running down and dripping off every rafter, all my tools, motorbikes etc were rusting terribly.
I tried 50mm insulation but the rafters were 1300mm centres, so over time the insulation has bowed (I should’ve put noggins in with hindsight), i counteracted this with battens underneath to hold it up, this helped loads but still not enough, so last summer I stripped all the metal off and put a moisture membrane over the rafters then put the metal back down, it’s virtually eliminated the sweating now, or it’s happening above the moisture barrier.
This type of roofing is really common in these parts and works well but they also do an insulated version and a version with a fibre membrane glued to it, specifically to stop sweating, I’ll use that in future applications.
Thanks for the input can you send a drawing so I can totally understand as its not quite clear I can then share this with others as it sounds like you have found a fix. info@londonflatroofing.co.uk
@@SteveRoofer basically like your house roof
thanks this is something i am doing soon. a big metal roof. what vapour barrier did you use?
I have the very same thing brick walls and tin corrugated roof and had water drips all over my stuff so I went to a carpet shop and asked them if they had any old carpets they chucking out they said yes in the skip at the back the shop filled my car up with of cuts and put them down on the garage floor stopped the drips over night even made the garage warmer and when working on my bike and car I was on warm carpet than cold floor ..
Put carpets down very easy prob to solve
@Plastic&paint me truly don't feel this is my remedy ..my roof needs addressing ..I've paid and ordered new screws with washers etc . Gonna put new beams up to . Coat roof sheets in bitumen paint . Smd go from there
Warm internal air holds moisture, if this warm air hits a cold surface it cools and condensation forms. Need to prevent a sudden temperature difference by using insulation between hot and cold areas. That white insulation stuck to the bottom of the metal will work work, thicker the better. I fixed a garage roof 15 years ago with exact same method. Its all about "relative humidity" ie hotter air can hold more moisture, as the air cools it cant hold the moisture so droplets of water form. You dont really want to be warming the roof, that looses heat which costs money.
It's about the dew point.
And where and how much insulation moves that.
Yes correct
Dew point or cold air bridging. As said warm air condensing on a cold surface. Like breathing on a window
I think in this case the source of the airborne moisture is the roof timbers and not the warm humid air inside the building (given it was not finished)
Possibly. The concrete blocks are a big thermal mass so continually warm the air and increase the airbourne mositure, then it naturally rises and dumps the moisture when it cools, then the cycle repeats. Single skin concrete block and steel sheets with no insulation are the worst case combination.
I bought a house with a double garage that has a roof clad in tin . In the summer it was like working in an oven, in winter it ran with condensation. I had the underside of the roof sprayed with foam in August 2003. I had to clear the garage before spraying and nearly melted with the heat even with all the doors open . Next morning the roof was sprayed and by lunch time it was finished. After lunch we returned to the garage and it was like stepping into a brick building out of the sun. This has been one of the best things I have done ,no more running condensation, no rusty tools making it a pleasure to work in. one mistake I made was I didn't cover the electric cables before spraying so if I have a problem in the future could mean a rewire. It wasn't cheap to do but the whole job including clearing the garage and putting everything back took less than 2 days . No signs of any rot in any of the timbers in almost 20 years
Ok thats good so this was some 20 years ago and no problems? What foam was it do you know? was there any smells or odors after as lots of people talk about problems with gassing off with spray foam
Would you remember what time of spray? Insulated spray?
I have an outbuilding at the back of my garden which has walls on the side with pebble dash, and wooden front doors with wooden struts running across the entire length of the ceiling structure, over metal struts, supporting the corrugated metal roofing above. And on the side of the outbuilding I have a sliding garage shutter door, which is facing a small plot of land that is higher than the foundation of the outbuilding, with a slope, leading into a long channel drain in front of the sliding garage shutter, that leads into a soakaway. When I moved in in 2017, the concrete floor had some cracks in it, but over time, since my soakaway has completely blocked up, despite putting a hose through it, and sliding it in and out to remove any debris inside, the cracks in my concrete floor, have got bigger on one side of the concrete floor, which wasn’t reinforced like the other half of my garage floor. I now have this problem coming off from the underside of my corrugated metal roof, drips of water, which is ruining my tools and other stuff inside my garage, and it has suddenly got really bad. I’m having a roofer look at it, but I feel I need to replace my damaged soakaway with a deeper channel drain, which runs along the entire length of the garage, instead of just in front of my sliding garage shutter door. It’s hard to explain, but the whole situation is now making me anxious, not knowing what should be my next course of action to remedy it, while worrying the cost might be huge. I’m just wondering would my house insurance cover this, or not? Thanks.
Great video and keen to see what the correct way of resolving this issue is. I also used this type of sheet to replace an old asbestos roof in lock-down. Same issue in my garage as the condensation at times drips all over the bikes/tools in the garage resulting in wet tools, shelving, bikes. Basically the contents it getting damp. Mine is just a garage so was thinking about 80-100mm insulation between joists and taping as this chap has done in his video but clearly that’s not the correct route. Real shame I didn’t buy the sheets that have the condensation backing on to stop this issue in the 1st place. Really keen to see how this is resolved as it sounds like the roof sheets need taking off to resolve correctly.
Yes this has been interesting I didn't know about condensation backing but have had someone reach out to me that has a outbuiling with them on and im going to see it next week so hopefully may be able to update this with another video
You need to understand where the dew point will be between the hot and cold temperature change and understand the thickness off insulation required to move the dew point to effectively manage any condensation forming. And yes sufficient through airflow will help keep the timbers dry and manage the roof as the weather changes
Some sheets come with the insulation attached, expensive though. My understanding is that the warmer air inside contains moisture that condenses on the colder metal roof sheet, depending on your local weather this may or may not be an issue.
Yes you need to keep the bottom of the metal warm
For something this size those panels can span 3m with only 1 support in the middle so even though the panels are more expensive, you save a lot in timber costs and labour since 2 people could put the whole roof on in a couple of hours...
This is absolutely correct, the reason you get water droplets forming is because of cold air has less capability to hold moisture than hot air. The air in the building condenses on the cold metal surface just like the effect of a cold drink in a glass makes moisture form on the outside of the glass.
The solution is really simple, apply insulation to the cold surface, preferably hydrophobic insulation or insulation with a hydrophobic coating. The plan should be for the insulation layer to be as tight to the metal roof as possible so there is no opportunity for air exchange against the cold surface.
I have an outbuilding at the back of my garden which has walls on the side with pebble dash, and wooden front doors with wooden struts running across the entire length of the ceiling structure, over metal struts, supporting the corrugated metal roofing above. And on the side of the outbuilding I have a sliding garage shutter door, which is facing a small plot of land that is higher than the foundation of the outbuilding, with a slope, leading into a long channel drain in front of the sliding garage shutter, that leads into a soakaway. When I moved in in 2017, the concrete floor had some cracks in it, but over time, since my soakaway has completely blocked up, despite putting a hose through it, and sliding it in and out to remove any debris inside, the cracks in my concrete floor, have got bigger on one side of the concrete floor, which wasn’t reinforced like the other half of my garage floor. I now have this problem coming off from the underside of my corrugated metal roof, drips of water, which is ruining my tools and other stuff inside my garage, and it has suddenly got really bad. I’m having a roofer look at it, but I feel I need to replace my damaged soakaway with a deeper channel drain, which runs along the entire length of the garage, instead of just in front of my sliding garage shutter door. It’s hard to explain, but the whole situation is now making me anxious, not knowing what should be my next course of action to remedy it, while worrying the cost might be huge. I’m just wondering would my house insurance cover this, or not? Thanks.
Excessive humidity was a difficult problem where I grew up on the west coast of California.
Where there are small attic spaces like this, once a good vapor barrier is installed, we generally installed some kind of powered ventilation fan to keep the outside air flowing through this gap and keep this area the same temperature on both sides of the metal.
If the temperature and humidity is the same on both sides, there will be no condensation.
Of course vents must be carefully installed so rain doesn’t get in there either.
I think we are moving towards adding powered venting and heating of roof cavitys in this country
I have built many structures with exposed metal roofing such as this in environments where the inside/outside temperature differential is up to 40c and the humidity 30/95%. The only proper solution to the problem of sweating is spray foam insulation (closed cell) applied directly to the metal to create a hermetic seal. It only has to be 2-3cm in thickness to be effective. Only ventilating/heating will only remediate the sweating, not prevent it. The foam panel amend open cell foam remediation seen in the video is not adequate as it still allows for a cold zone next to the metal causing the condensation. I hope that helps. Good luck.
Yes that seems to be the way everybody things he should go
I have an outbuilding at the back of my garden which has walls on the side with pebble dash, and wooden front doors with wooden struts running across the entire length of the ceiling structure, over metal struts, supporting the corrugated metal roofing above. And on the side of the outbuilding I have a sliding garage shutter door, which is facing a small plot of land that is higher than the foundation of the outbuilding, with a slope, leading into a long channel drain in front of the sliding garage shutter, that leads into a soakaway. When I moved in in 2017, the concrete floor had some cracks in it, but over time, since my soakaway has completely blocked up, despite putting a hose through it, and sliding it in and out to remove any debris inside, the cracks in my concrete floor, have got bigger on one side of the concrete floor, which wasn’t reinforced like the other half of my garage floor. I now have this problem coming off from the underside of my corrugated metal roof, drips of water, which is ruining my tools and other stuff inside my garage, and it has suddenly got really bad. I’m having a roofer look at it, but I feel I need to replace my damaged soakaway with a deeper channel drain, which runs along the entire length of the garage, instead of just in front of my sliding garage shutter door. It’s hard to explain, but the whole situation is now making me anxious, not knowing what should be my next course of action to remedy it, while worrying the cost might be huge. I’m just wondering would my house insurance cover this, or not? Thanks.
Whenever installing single skin sheeting I would always advise an anti condensation ‘Drip Stop’ sheet. This has a fleece backing to the underside of the metal which stops the condensation from forming into droplets and allows the ventilation to dry it out. The bottom 100mm of fleece should be cut back to stop moisture drawing back. Otherwise a double skin build up system should be used with a mineral wool insulation between the two metal skins. This is standard in commercial buildings.
With kingspan and other insulated panels the price may seem expensive in comparison on the face of it, but once you calculate the materials required to install insulation correctly with a double skin system the price becomes very competitive, easier to install and a much nicer interior finish (white lined)
The money being spent here to stop the condensation and hassle could have been negated with a composite insulated panel.
Yeah absolutely agree with you I didn't know about the one with the fleece in the back I'll look it up. Thanks
I have an outbuilding at the back of my garden which has walls on the side with pebble dash, and wooden front doors with wooden struts running across the entire length of the ceiling structure, over metal struts, supporting the corrugated metal roofing above. And on the side of the outbuilding I have a sliding garage shutter door, which is facing a small plot of land that is higher than the foundation of the outbuilding, with a slope, leading into a long channel drain in front of the sliding garage shutter, that leads into a soakaway. When I moved in in 2017, the concrete floor had some cracks in it, but over time, since my soakaway has completely blocked up, despite putting a hose through it, and sliding it in and out to remove any debris inside, the cracks in my concrete floor, have got bigger on one side of the concrete floor, which wasn’t reinforced like the other half of my garage floor. I now have this problem coming off from the underside of my corrugated metal roof, drips of water, which is ruining my tools and other stuff inside my garage, and it has suddenly got really bad. I’m having a roofer look at it, but I feel I need to replace my damaged soakaway with a deeper channel drain, which runs along the entire length of the garage, instead of just in front of my sliding garage shutter door. It’s hard to explain, but the whole situation is now making me anxious, not knowing what should be my next course of action to remedy it, while worrying the cost might be huge. I’m just wondering would my house insurance cover this, or not? Thanks.
@@lg_believe333 unless this had been stated in your insurance policy, I would be surprised if this will be covered. It sounds like it is either very old and in disrepair or badly built. Insurance policy tends to cover things like storm damage. The only way to find out is to contact your insurers and ask the question, it won’t cost you anything to find out directly from them.
Coedri
I have the tin sheets on my garage with the 'anti con' fleece on the underside, i personally think theyre terrible. Terrible condensation in the garage with plenty of air flow ! I have since been advised that those sheets 'shouldnt' be used on a pitch less than 15°
I had exactly the same problem with my open carport(closed on 3 sides), it would get so much moisture accumulating on the underside of the tin just like this. It drove me crazy, dripping all over my motorcycles and I couldn't store anything in there without it getting wet. All I did was install corrugated iron on the underneath of the timber beams creating an air gap and the problem went away. No insulation, just creating a temperature difference between the top layer of tin and the bottom layer of tin.
Interesting, you changed the internal environment! Let's think that though, you didn't change the roof so the underside of the roof was always the same temp, so by adding a metal under the ceiling you formed a small ecosystem between the two, you also stop the underside of the old roof from getting to the atmosphere of the entire room. So how did it work? probably less moister getting to the underside but apart from that I dont know
BazzaDawson I agree with what you've done....best way.
Steve Roofer:
You will probably achieve the same results with a sheet of plastic DPM stapled to underside of joists. Much simpler, and cheaper!
I built my garage with the same box steel sheets. Had the same problem with tools going rusty with dripping condensation.
I waited until summer months, filled inbetween timber joists with Rockwool insulation. Then stapled a sheet of Visqueen DPM to underside of joists. Followed by plasterboard screwed to said joists then skimmed with plaster. That was 5yrs ago, I've had no trouble since. No more baking hot in summer! No more freezing damp in winter! Hope this helps.
Yes I know that works unfortunately its knot recognised as being the correct way of doing it by building control but for a shed or workshop that works
I guess it gives ventilation plus warming the underside of roodmf sheets this I may do on mine it def needs doing it's winding me up but I'll likeky put new rafters in as I think the past damp has weakened the rafters
I have a layer of DPM on my sheds metal roof already, do you think filling this with rockwool and then covering with tongue & groove pine panelling would work the same? Wana avoid plastering etc if possible.
I have an outbuilding at the back of my garden which has walls on the side with pebble dash, and wooden front doors with wooden struts running across the entire length of the ceiling structure, over metal struts, supporting the corrugated metal roofing above. And on the side of the outbuilding I have a sliding garage shutter door, which is facing a small plot of land that is higher than the foundation of the outbuilding, with a slope, leading into a long channel drain in front of the sliding garage shutter, that leads into a soakaway. When I moved in in 2017, the concrete floor had some cracks in it, but over time, since my soakaway has completely blocked up, despite putting a hose through it, and sliding it in and out to remove any debris inside, the cracks in my concrete floor, have got bigger on one side of the concrete floor, which wasn’t reinforced like the other half of my garage floor. I now have this problem coming off from the underside of my corrugated metal roof, drips of water, which is ruining my tools and other stuff inside my garage, and it has suddenly got really bad. I’m having a roofer look at it, but I feel I need to replace my damaged soakaway with a deeper channel drain, which runs along the entire length of the garage, instead of just in front of my sliding garage shutter door. It’s hard to explain, but the whole situation is now making me anxious, not knowing what should be my next course of action to remedy it, while worrying the cost might be huge. I’m just wondering would my house insurance cover this, or not? Thanks.
The timber often supplied has lots of moisture it particularly the treated variety. Just let it dry out will take ages. Get a sample bit of wood dry weight it and they force dry it and see what it's after.
When my garage flat felt roof started to leak, I replaced it with metal roofing panels. I have never had sweating problems. Mind you, I had the foresight to use insulated roofing panels. I suppose you get what you pay for.
Yes thats what saved the day
So many people rushed to build these in lockdown... What with all the "experts" rushing to cash-in, I imagine they'll be providing content for years to come.
Great video as always Steve. The best videos about roofing on TH-cam
Wow, thanks!
I'd suggest that the full insulation sheet/tape seal up process shown on the photo will do the job. Eave venting the underside of the roofing flutes is probably counter productive at this point. He only needs to raise the bottom metal surface temp a few degrees to move the dew point slightly. It's common to install fluted metal roofing over plywood or thin rigid insulation sheets; doesn't take much in terms of R-value to solve a dew-point issue. He can finish sealing the underside as he was doing, and perhaps follow up by removing a couple small insulation sections at a later date to check for condensate.
🧐hmmm… That’s kind of my other idea I’m thinking about. Removing the tin sheets and overlaying the whole joist area with 25mm polystyrene (all joints taped) and sitting the tin sheets back on top.
The little test square I did had no condensation on it at all. I just worry about what might build up between the polystyrene and the tin sheet over time.
@@MatLampitt There's very a good chance it will be fine as is. To be certain I'd periodically remove and check above inspection panels before installing a finished ceiling. In reality you've accomplished mostly the same end result as pulling up the tin and reinstalling over insul board, your present cure was slightly more complicated of course:). As mentioned, achieving a good vapor barrier between the living area and the underside of the tin will serve to reduce condensate opportunities. Example..if you choose to ultimately install a finished drywall ceiling, look into paint priming the drywall with a vapor barrier product (basically a solvent based primer similar to Bin Seal)
It looks like you're doing a good seal-up job with sealant, tape and panels.
He can take the sheets off and put a DPM on top of the joists. Then put lengths of roofing batten on top of the joists to raise the sheets, then put the sheets back on. Make sure that the air can now circulate through the new void.
This is correct he is missing the roofing battens that you use with metal roofs
Hi buddy, yes I think that’s what I’m going to do with it. I thought the airflow provided through the shape of the roof profile would be enough but it’s not the case. Even with 6 x32mm holes drilled in the top of the centre noggins.
Thinking either that or take the sheets off and layer it with 25mm polystyrene or kingspan and pop the metal sheets back down on top of them.
Ok let me know how it gos
In the past on out buildings, even little cabins I have insulated between the rafters then tyvek then Perlins then tin, the perlin and under tin area is fully vented front to back. My theory is the most damp air travels through the tyvek onto the under side of the tin and drips back onto the tyvek and runs or evaporates away. Hope that made sense
@@elliot8595
The joists act as a batten, they're no different.
When I done mine I used 18mm OSB then covered it with rhino breathable membrane then added the metal, solid roof with no issues.
Did u have good ventilation under it ?
@@SteveRoofer yes! I used the 6x2 to block both ends then drilled a series of 10mm holes at the front and back then got some filter wool and stapled them on the backside of the 6x2 to stop insects/dust getting through.
So the hypothesis here is that your metal will weep, but will drip onto the membrane and run harmlessly away?
@@AndrewHelgeCox yes! Basically I left gaps on the foam weather strips on the bottom to allow any condensation to run away..
@@AndrewHelgeCox
Yes, it's a vented build up.
The air gap moves moisture away
I saw a lot of metal roofs on residential properties in the mountains of Southern Poland. Places at altitude where external temperatures drop below -30°C in winter. It must be possible to stop the weeping condensation or somehow have it not matter.
Yes basically use the metal roof like an umbrella over a warm roof is what they do
Would of been better to have not used metal from new but here we are.I have just finished a project where we had bad condensation from a metal roof, I used a spray foam from EPS Systems not the cheapest but it has 100% worked stops all drips.I wouldn’t normally use spray foam as all the horror stories but as it was onto metal I can’t see it being a problem.Hope that helps
Thanks
Wrong sheets for job ....should of had anticondensation backing on the underside.....there's plenty of air circulation through the corrie's..the bare metal will always condensate...especially when the building is warm and roof is cold...done a good job of insulation so could be lucky and never notice when it's plastered
Tell me about it 🤦🏻♂️ I didn’t realise there was such a thing until it was to late. Lol
If it's happening behind closed doors, it's still happening whether you see it or not.
And that will cause the timber to rot, but you can't see it happening.
Late to the comment, but as a metal building contractor for over 20 years you are correct. And spray foam is just as bad.@Robert-cu9bm
That’s not sweat it’s condensation, once the building dries out the insulation will stop the warm moist ambient air reaching the cold surface and condensing.
Your right but most people refer to it as sweating your wrong re it will go away read the nightmare others are having
Think I would have OSB it, then breathable waterproof vent membrane, battern it then cover in tin creating an air gap
Wouldn't a desiccant humidifier, used as and when required, dry out the whole building?
Good explanations 👍
It would be prudent to cover all block work during construction, and install drying equipment, to reduce this initially. I’ve data logged about 60 roofs, and found roof condensation can occur in most roofs intermittently, and doesn’t normally become an issue. If you have timbers that get wet, and don’t dry out quickly , because of restricted ventilation, or poor detailing, timber decay can occur. Just as a point of interest a house roof will reach 40 degrees in the summer with very high dew points, and massive vapour pressures. This is called summer condensation. Vapour pressures in winter are low because it’s cold. If anybody has data logged a roof like this I would be interested to see the data👍 That roof to me looks destined to fail.
Im looking that up also looking in to vapour pressure more as its an interesting subject
@@SteveRoofer best way to measure movement of moisture bud 👍
It would be good to know what the guy eventually did and if it worked or not Steve.
Ill trey to find out
Fleece backed metal roof sheets work well but to be honest he really needs a OSB or ply roof with two layers of torch on felt, EPDM Rubber roof or a GRP fibre glass roof.
The building might be in his Garden its being used as a proper room not a shed.
The general consensus here is that he should've used insulated metal roofing sheets and that will resolve the problem
Put windfoil on top of the rafters and cross batton over it and then the metal
3:22 on the question of adding styrofoam:
His idea should be good. Keeping the warm, moist air from touching the cold metal (every evening I assume) should prevent condensation.
Alternatively, he could allow for some way for the outside air to continually flow under the metal (and above his insulation), which is supposed to keep it dry. If the humidity is high outside, I have my doubts about this one.
You talk about the second one fitting the roof, theoretically what you’re doing is forming a cold roof put the metal transfers. The outside temperature down so much that the underside will always have condensation on it. If the outside temperature drops and the relative humidity is high, We see this a lot in garden sheds that have a lot of natural ventilation, but still the metal roof still gets condensation on it
looks like the shed is built on a concrete slab thats exposed to the wet on the outside and will soak up all the wet like a sponge or am i seen things ? Also is a comcrete slab not just for a woonden shed or something and they should have dug out trenches to build the walls up on to damp proof course.
What would you advise for a new metal roof on top of wood sheathing wood sheathing? Insulate the attic floor and ridge vent (cold roof) or spray foam above attic plane with no attic venting? Or something else? Thank you for your informative work.
attic vent and make sure any metal roof has some sort of insulation to it or it may get condensation on the back
Thanks. Unclear as to how to deal with humidity build up on the inside of a spray foam insulated attic without venting. This was recommended by an insulation company. We live in Midwest US temps can float fro -20F to 100F and we like having our doors and windows open. Makes more sense to add insulation on attic floor, vent soffits and attic box vents(?)
Putting metal roof on this summer.
I thought with the bare metal inside would get even more moisture if you increased the internal heat due to heat condensing against the cold from outside.
Im now confused to how adding insulation to the inside of the joists with a vapour barrier and increasing the airflow between roof void wouldnt help it all.
It isn't heat that is condensing, is moisture in the air.
So keep the heat in with insulation, the due point is on the metel. Take the insulation out and let the heat rise.
unfortunately that doesn't work it lets all the heat out and then when all the heat is out the roof gets cold and then you get condensation again
Kingspan 40mm insulated panel should have been used instead of single skin sheets. We have solved this sort of problem by putting battens on top of the existing roof and put fiberglass type insulation in between the old and new outer skin single skin sheets
Use a Kingspan insulated metal composite roof panel
Yes that seems to be the correct answer however both the man in the video and I had never heard of one until people like yourself gave us your wisdom thanks
Thank you Steve.
Thanks for watching
Doesn’t matter if you had full open walls rather than windows and doors because at night the metal roof radiates heat to space faster than anything else and any atmospheric moisture preferably condenses on the roof.
Whilst it seems an issue now the on site construction moisture is in the long term irrelevant, it would still ‘rain’ indoors decades later when the humidity is high and the roof radiates to space overnight.
The fix? Either insulated metal panels, or, in order from the top, uninsulated metal sheet (the underside being vented) taped tyvek on structural OSB, over 100% cover PIR insulation (even 25mm would be sufficient) and a vapour barrier. The existing timber roof structure, now under the new vapour barrier can remain open to the occupied space with no cold bridges.
Internal moisture does not go beyond the vapour barrier, any external moisture still condenses on the metal sheet but above the tyvek where it can drain off or evaporate during the day.
Some good points i'm not quite suer about the buildup ill draw that out on paper and think about it
Yes, it still has big buildups of condensation and the building and surrounding area are so much dryer now lol 🤦🏻♂️
This sounds similar to one of the other options I was thinking about.
From top to bottom:
Metal sheet
Directly on top of a breathable roofing membrane which is directly on top of a layer of 25mm insulated sheet, Either Foilbacked pir or polystyrene Jablite
So basically was thinking sandwiching the 25mm insulation of choice (probably polystyrene because it won’t have the foil backing that also condensates in cold) between the tin sheets and existing joists. And still retaining the ventilation underneath the polystyrene as that won’t be for the purpose of keeping heat in but rather keeping air away from the internal layer of metal sheeting.
I would then put back the 100mm pir and tape the joints.
I can definitely see the use of a vapour barrier where you said but what’s the purpose of the extra OSB ?
Also is Tyvek just breathable roofing membrane or something fancier ?
Seems there are a few ways to redo this so want to make sure I make the best choice.
@@MatLampitt Tyvek Supro, breathable but also water repellant.
The insulation (regardless of the foil facing pir is preferable to polystyrene) is loose laid on the roof structure, the osb (11mm is sufficient) is then screwed down sheet by sheet through the insulation into the roof structure making a safe walkable platform, the tyvek is stapled onto the osb (it needs overlapping and taping with the appropriate tyvek tape and while it could be laid over just the insulation doing so makes fitting the metal roof precarious.
The metal roof essentially becomes the primary means of avoiding rain penetration, the tyvek the secondary. Direct fixing of the metal roof with tekscrews into wallplates fixed over the tyvek with the tyvek extending behind the facia boards ensures you don’t have any wind blown moisture problems.
The metal roof effectively becomes something to keep UV off the tyvek.
Cheers martin.
Yeh can see the the point of the OSB now.
So if I was to redo the roof with this method using 25mm pir then would I be able to push the 100mm internal pir up to the underside of the 25mm and the only ventilation needed would be effectively between the raised sections on the steel sheets and the Tyvek?
Also you say no cold bridging on the joists but I think there still will be a bit from the front and rear facia.
Can you do a video on underlays in pitched roofs? Lots of them are getting installed tight as a drum - does this have any implications other than vibration noise etc?
All day today Ive been building a test rig to demonstrate that and lots of other things so keep an eye out. How do you get to see such things?
I bought a new build and at night the horizontal laps were buzzing like angry bees.
Coat the top with a white rubberized top coat to significantly drop the temp of the metal.
No won't work painting black would be better but still wont work
Im getting a metal shed to use as a games room / home office. I'm planning on using double sided foil wrap close to metal wall and roof as my radiant barrier, then kingspan boards and then interior wrapped with vapour barrier and them covered with plaster board. All relevant gap tapes used also to seal joints etc, would this be the best way to keep heat in and cold out and stop sweating. Iv heard overkill but better safe then sorry
Well as per the other comments on here the way to go seems to be to get the metal roofing that has already got insulation attached to it
Hi, I’m building a very similar project and will be using metal sheets for the roof, but I was going to felt and batton it like a conventional roof then insulate between rafters.do you think tgg be at would be ok please?Gareth.
Why not take the metal roof off, add a plywood roof with lightweight felt and then refix the metal onto that, then under the plywood re add your insulation panls?
Yes however the consensus is to take the metal off add breathable membrane and battens and then put the metal back on same as your idea in a way
What are your thoughts on insulating shipping containers, difficult to find advice from those living in the UK. Its framed out and I am considering rockwool and a vapour barrier
I have tin sheets on my garage with the fleece 'anti con' lining on the underside and still get terrible condensation with plenty of airflow into/out of the garage. I have a couple of rolls of 100mm loft roll, and thinking of using the 100mm loft roll uder the tin sheets and then underboarding with ply wood. Whats peoples thoughts on this ?
Hi, I'm currently working on a commercial project, we have a flat roof and we are planning on using a single ply roof system on a metal deck. I would like to know if i need to place a vapour barrier on the metal deck before i lay the insulation?
Yes you put a vapour barrier on the metal deck probably you would use Alutrix 600 because it's sticky back and you don't want to be mechanically fixing it down
@@SteveRoofer Thank you.
Roofing felt under the sheets would drain any drips wouldn't it? [I have now seen tis mentioned below but will let this stand]
Yes that seems to be the consensus
the condensation will just be on the underside of the membrane.
Better off using sips panel or EPDM rubber roof.
Yes agree
Would have been better to use the twin wall sheets with insulation built in the Center .. we use them on commercial building and see little or no condensation..
Thanks
Hi sir can you halp me i made one same house this few days but i get seme problem in my house if some time sun and some time rain after come more moisture in said the metal sheet how i resolve this issue
Around the christmas time my bedroom ceiling and wall surrounding the window (dry broad wall and plug socket is soaking wet) has starting sweating a lot, to the point you can hear water droplets fall on to furniture throughout the night, every day i had to wipe it dry, i refuse to have the windows open throughout the freezing cold nights, do you think that’s the problem, it only happened since i moved into the bedroom
Steve I have a new Welch blue slate roof fitted recently and noticed the ridgeboards wet with crystals all over it now. Should I be concerned???? I haven't closed the ceiling yet but maybe thats the problem?????
Yes possibly the problem as you are letting moisture get to the roof. Make suer its vented correctly
Should have asked before you started .and put none con non drip sheeting on and problem solved
Good tip!
Hey Steve
We have an enclosed patio area with plain metal roof sheeting. Winter condensation drips.
The paint is perished over probably 30 or 40 years.
Would painting the outside of the roof sheeting help stop this please?
Many thanks
No but glueing some sort of fabric
Over it may help some sort of fleece material what happens is that it holds the moisture until it evaporates
@@HampsteadBuildersLt Glue fabric on the inside? Many thanks for your reply
Should of just bought anti condensation sheets single skin with fleece on bottom. Best thing he can do with that is get a bar system like ashgrid and build roof up ie twin skin with loose lay quilt insulation but all his fascia heights would have to be changed
he didn't know about anti condensation sheets when he got his
Hi Steve.this is probably a stupid question ,should there be insulation between joist in my new warm flat roof. Thanks
Not normally but if sometimes if room above is tight. generally it can be calculated that if you have approx 30 of the insulation under the decking tight to the decking and the remainder above that works
Venting at the top and not the bottom end of the soffit would have been smarter
Yes would have solved part of the of the problem
Hi Steve, do you think adding 25mm battens as purlins would give enough ventilation to avoid sweating for this build. Or will sweating occur either way as it’s a metal roof? If it’s a still night with little wind for ventilation for instance I’m not sure if enough air movement would occur.
Its alway going to happen with a metal roof he needs to insulate the metal to keep the bottom warm
Ideally you have sheathing over your rafters with roofing paper and ice/water protection. Then you have a ventilation matt or wood strapping between your metal. Whenever water condensates the gap gives the water somewhere to escape. It really brings up the cost but it's best practice.
How do you stop an open carport with a metal roof from sweating?
you insulate it
@@SteveRoofer Using? I've seen spray foam used and it still sweats.
What is OSB?
oriental strand boards basically a replacement for ply
No solution offered!!! 😤
No, but all the solutions are actually in all the comments
Using a dehumidifier wouldn't be a good idea.
Yes but why mechanically remove the moisture when you can do it naturally
@@SteveRoofer in the situation it's the best option. Tell me how you would do it naturally?
@@donalrodgers123
Airflow.
Thats the solution ive been using in my concrete garage with metal roof until i can come up with a permanent fix, also have a, tarp at an angle keeping water off the bikes but even with a decent sized dehum running still get a lot of moisture in cold weather. Thinking of binning off the metal roof altogether and going for rubber or felt tbh
0:25
the roof needs to come off, lay roofing underlay over 75mm netting.
Not the consensus on the comments below
Try shooting at your shed or garage, preferably from a helicopter This should stop it sweating, at least for a few years.