How Vapor Barriers Work
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- Опубликовано: 15 янв 2016
- Building and renovating homes in cold climates requires vapour barriers in some places. Learn how the work and why they're essential. Courtesy of Steve Maxwell @ baileylineroad.com
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From US Department of Energy: " If the outside air is colder and drier than the inside of a home, then moisture from inside the warm house will try to diffuse through the walls and ceiling toward the cold, dry outside air. If the outside air is hot and humid, then moisture from outside will try to diffuse through the walls toward the dry, air-conditioned inside air. We used to tell people to install vapor retarders to try and stop this moisture diffusion. But we have learned that if moisture moves both ways for significant parts of the year, you're better off not using a vapor retarder in the walls at all."
I think it depends on the climate zone. If in the coldest zone then you should use on on exterior. But that's only a small section of USA, but much of Canada.
Their site doesnt say that rofl. www.energy.gov/energysaver/vapor-barriers-or-vapor-retarders
Great job! If only everybody would make videos as succinct as this!!!
Thank you! Straight and to the point.
amazing video!
There's a big difference between an air barrier, vapor retarder, and vapor barrier. You don't need a vapor barrier to stop air movement, you need an air barrier. If you also need to stop water vapor from diffusing through the wall, you can include a vapor barrier. Normally the diffusion rate is not high enough to actually require a vapor barrier, which can also trap moisture inside the wall cavity if it gets in there. An airtight assembly using only drywall with a layer of paint is enough of a vapor retarder to essentially remove the possibility of condensation in the wall in most climates.
Thank you 🙏🏼
Helpful af ❤
wow great video
Simple explanation, but very effective indeed 👍 Thanks for sharing mate
Glad it was helpful!
@@baileylineroad
@@baileylineroad Thanks. 1 zubs and 1 like done. Mine as well, if it's ok. 😀. Thanks.
good
Great video. I have a question. Regarding a cantilever d floor. Do I need to put a vapour barrier on the warm side of the floor and then install my plywood? Thanks so much.
Hi Steve! Thank you for your videos they are always so helpful. I have a question I am hoping you can lend your expertise ...we recently had " wet" cellulose sprayed in our walls, we noticed that even after 2 months of dry time before Sheetrock we have quite a bit of condensation on the inside of the sheething and first inch or so of the cellulose insulation when we reached our hands in to check. It has been below zero here lately and we keep the radiant in floor heat at around 70 to make up for not having Sheetrock yet etc. Is this a normal occurrence given the temperatures? Or do we need a vapor retardant in our area of CNY? No one has any answers for us, everything we read offers contradicting ideas and we are prettified of doing the wrong thing and getting mold in our forever home. Any advice you can give will be truly appreciated!!!! -maggie
Thank you for this video. I just built the external walls with windows around my front porch using OSB boards and plastic siding. Further, I plan to insulate these and finish the walls inside with cement board panels, just because the walls might have water condensation on them during the cold weather. Question - do I need to install the plastic vapor barrier or the cement board can work like a vapor barrier? I have seen some videos on RUclips where the mold was growing behind the plastic barrier on the insulation batt.
Sir, I have a question: How to insulate properly a concrete wall to prevent moisture? What should be done on the warm side of the wall before one builts a wooden frame?
Subscribed.
Vapor barriers also stop air circulation through and around the insulation that WILL defeat the best insulation. So even if Code doesn't require it, you need your insulation to not be defeated by drafts.
How much would it effect or make a difference if I'm installing Henry Blue Skin on the exterior walls on my 167 yr old farm house
Excellent presentation by using uncomplicated sketches to demonstrate the explanation. Also great narration voice, which is getting harder and harder to find.
Steve. Simple and to the point. Thank you. And then I read a question asking about seasonal changes swapping the warm and cold sides!!! I hadn’t thought of that so Im wondering if it is really that simple?? Can you explain please??
My understanding is that you need to determine if you have more heating days vs more cooking days. If you have more heating days then the vapor barrier goes like he demonstrated.
Not sire of I'll get a reply but my issue ir corrugated roof sweating . I had a hunch that fixing barrier to underside was not going to work ..I need to put new wall plate and beams on anyway ..wouod you suggest new sheets ? Anti condensation ? Or as a mate suggested . Osb . Then membrane then sheets (corrugated ) ? Thanks
Question: I am finishing the basement. I plan on putting rigid foam board on the concrete foundation walls and then building my walls an inch out from the board. The Foam board will count as a vapor barrier as far as stopping the outside cold from coming in. Do I need to also have a vapor barrier on the interior wall between the insulation/framing and the drywall? Which would be a total of 2 vapor barriers.
This is the one question I have not found a clear answer for yet.
Do we need to put it if we use mold sheet wall?
Hi Steve, this is a great video. Question though, what about change in seasons? The warm and cold faces of the wall will swap therefore meaning the vapor barrier will need to be on the other side. How does that work? Im planning on insulating a shipping container but want to do all I can to avoid mold. I also don't want to use closed cell poly foam because of the off gassing. Do you have any advice? Thanks so much
You just have to choose based on which is more prevalent. The metal of the shipping container is obviously already an air and vapor barrier. You need to worry about not only mold, but also potentially rust. You can cause problems by making a vapor impermeable sandwich, trapping moisture between two vapor barriers. Insulating on the exterior of the container with a continuous blanket of rockwool or EPS is likely the ideal solution. In that case you'd have to set the container on top of insulation as well. Create a ventilation gap on the exterior of the insulation and then a waterproof+siding layer and it should be fine in most climates. See "perfect wall."
I read that there is need for a Vapor Barrier if the insulation is less than 200mm (7.9 inches). The moisture can't condensate inside insulation of lesses thickness (they say).
Thanks for your note. I really boils down to the type of insulation. You could have all the fibber-base batt insulation you want in a wall, and condensation will form no matter how thick it is. That's because air can move through the whole thing. By contrast, you can have only three inches of extruded polystyrene and it won't allow condensation. That's because air can't pass through it. Does this make sense?
Take care and thanks for watching!
Steve
Hello. Im from a tropical Contry (Costa Rica) and here is sunny and rainy but never snowly. Consider you necesary install membrain in both(inside and outside) of a wood wall?
No? You only need it if it gets to below freezing or is in the lower tempatures.
Question- I thought there should be another vapour barrier also next to the outside foundational block wall because the outside blocks are porous therefore they will absorb water from outside into the block …I thought that you don’t want the moisture being drawn in through this porous foundational block to touch the insulation thus poly encloses the insulation on both sides ….
Should I worry when I drill a hole to mount something on the wall and it makes a hole in the vapour barrier?
What if you are in a temperate area where the warm side reverses from winter to summer?
I like how you draw out your videos. How do you do it?
Camera aimed at a large photo that he draws on while explaining in real time. As well as a good quality headset mic I imagine
+D Drapes Excellent vid!
What about people who hang pictures and clocks on the wall. Do they get mold?
I know this is a old video but what about areas that see different seasons, snow during winter and hot in summer? Which side do you install it on in this situation where the hot side will change per season? Thanks.
Look up the building code for your region. It's based on whichever is more prevalent.
hii,
Matt the build show guy said no vapour barrier is needed inside the house.. so, why should anybody install membrain in the first place ?
we can never seal air until perfection, if install polysheet , surely after sometime moisture will be trapped.
I am building a tiny house out of a 20ft container, I am using InsoFast foam board insulation that form fits against the corugated steal, but wanted to put a vapor barrier between the foam board and the drywall, would this be a good idea, using this membrain stuff? BTW, I am in New Hampshire, so plenty of humidity and cold weather.
Foam board acts a vapor barrier if its sealed up well enough.
if you install vapor barrier inside then then it will dry outside when heating . if you install vapor barrier outside then it dries inside when its warmer outside than inside. Never install anything between two vapor barriers. container itself is a vapor barrier
Do they use regular plastic because vapor barrier is for the floor
So what stops vapor from collecting on the backside of your sheet rock?
It should be a sandwich, it is explained in ruclips.net/video/D7BzkzDMWgY/видео.html
Sure*
What would happen if you installed the vapor barrier on the outside wall I live in Ireland
Benji newing lol I’d say pop another Guinness mate
unclear on something. You'll prevent moisture from occurring on the insulation, but the back of your drywall may condensate and not dry. How is that handled?
Where can I buy Membrain poly?
Kimberly Bainum
BAD idea!
So this minimizes thermal bridging?
Well, no. Thermal bridging happens most commonly when heat/cold is conducted through solid wood studs. Vapour barriers are just ways to stop internal condensation in fibre-based walls.
Thanks for watching my videos!
Steve
Membrane
I think you need extreme climates to justify a vapor barrier, either south florida heat or canada cold extremes, everybody in the middle doesnt really need one. The vapor barrier will also be different based on cold climate or hot climate.
You didn't need to make a 23-minute video with interspersed messages from sponsors to explain this? Thank you.
vapor collector, not good
Wrong! An internal vapor barrier (thin sheet of plastic) does not keep warm air from penetrating the wall! And in the summer all it does is trap condensation buildup (when warm humid air from outside is coming through the wall into cool basement) and create a perfect environment for mold to grow.
Hi Jack,
Where do you live?
Steve
Hi Steve. I live in MN. FYI, I live in a house that isn't even 5 years old with a basement has the exact same insulation/vapor barrier setup you are recommending in this video...and there is mold growing inside the vapor barrier across the entire basement. I refer to it as a mold curtain and many neighbors (with homes as new or newer) are having the exact same experience (and those who are still unsure are unable to see because they have already finished their basement...now wishing they hadn't). In looking into this as much as I have, I'm absolutely dumbfounded that this method is still being recommended. Interior of walls will undoubtedly get condensation buildup when humid air from the outside reaches the cold surface on the inside. Just use the simple example of how in the summertime the exterior of a glass containing a cold beverage sweats with condensation. All vapor barriers do is reduce or severely limit the wall's ability to dry on it's own by trapping the condensation building up and not allowing it to escape and ultimately dry. Wall's need to be breathable and vapor barriers do not allow for this to take place. What's even more of a head scratcher is that vapor barriers are still written into residential building code for MN. I've spoken with several contractors, mold abatement companies and even a former member of MN Residential Energy committee (who is also a building scientist, a registered engineer and a certified industrial hygienist) and they all unequivocally agree that vapor barriers, though well intended, do much more harm than good and that walls have a much better chance of remaining mold free by NOT having a vapor barrier. They all speak from years of experience having looked at hundreds of homes (probably thousands added together). Needless to say, I am a bit passionate about this right now and I do not mean to insult you or speak derogatorily towards, so I apologize if I come across that way.
Hi Jack,
Thanks for your note. I understand. Basements are entirely different situations that above-ground walls. I always advocate against using vapour barriers in basements (as well as the kinds of insulations usually used with vapour barriers). And yes, many vapour barriers are installed poorly in above-ground walls, too. But the fact is, if a person is using any kind of fibber-type insulation, then if you simply go with no vapour barrier on the inside, you'll have rot in a few years. A properly installed vapour barrier installed in an above-ground wall in a cold climate does work. It's the only option for using any kind of fiber-based insulation.
What's your strategy to fix your basement?
Bye for now,
Steve
Thanks for your reply Steve. Maybe we're on the same page after all. I thought you were referring to vapor barriers for basements but sounds like I was misunderstood so I apologize. Not yet 100% certain with my strategy yet but I'm thinking for now to fix the basement (after tearing out current vapor barrier, insulation and cleaning any remaining mold from wood studs) is to first install 2 " XPS rigid foam insulation board with a R value of at least 5 and then follow that up with either another layer of XPS rigid board with same R value or batting with equal or greater R value. My goal is to create an R value minimum of 10. After that I plan to cover with mold resistant drywall leaving an inch or two of space between drywall and insulation for the wall to breathe. Also will be purchasing a decent dehumidifier to run down there during the warmer months of the year. That's at least what I've come up with so far. Also, even though it's code, I'll probably be "forgetting" to put up the vapor barrier before putting up the drywall. : ) Anything you see that could improve in strategy? Thanks.
Jack - What you are saying is exactly what I'm dealing with at the moment. Our newer home (now 9 years old) had vapor plastic barrier installed on the basement walls (over studs and insulation). It's a walk out basement and the past couple of summers we've noticed a slight musty smell, but it's a fairly new home (about 6-7 y/o when started) and super clean with no water whatsoever. We could not figure it out. The smell left after say August. But this summer, because it's been extremely humid and muggy (here in New Hampshire), the smell got worse and we just realized all the insulation was growing black mold where the insulation meets the plastic. The hot air from outside (90+) was meeting the cold air in the basement (72) and just bred mold.
The easiest barrier is OSB. Use it inside and not outside. Outside tyvek is enough. And you have a diffundation Niveau falling direction outside.
Membrane