The Ugly Truth About Basement Vapor Barriers

Installing a vapor barrier in the wrong location in a basement wall can end up trapping moisture in the wall assembly and supporting mold growth, leading to the rapid deterioration of the interior framed walls and finishes. It is better to not have a vapor barrier than it is to install one in the wrong place. In this video, we dive into the science behind vapor barriers in basements as well as some best practice strategies to provide interior moisture control without compromising the integrity of your home.
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[@gnargnar1992]

Probably the most underrated building engineering channel.

[@RatedCfm-cz8ff]

In western Canada, it was code for many years to have vapor barrier between the concrete wall & framing, as well under the drywall. The building code changed in the late 90s, no more vapor barrier permitted between the concrete wall,.& the framing. It was discovered that moisture was building up in between that vapor barrier, & the concrete, mostly from frost build up during winter months. The moisture would remain almost indefinitely, and emit a mildew odor, usually at its worst in the early spring.

[@pwblackmore]

There was a lot wrong with the BC building codes previously... 'leaky condos' being one prime reason for change. Water is the enemy of wood... do whatever you can to eliminate its ingress from outside first. Then make sure whatever is inside can breathe its way out.

[@Googaliemoogalie]

My home was built in 2003 and has a vapour barriers on external walls. Over insulation and studs

[@stonecoldcustoms]

Great video - Amen! It took me 15+ years of home ownership before I learned this the hard way. Eventually figured out that no vapour barrier and rigid foam is the only way to go!

[@timothychung4811]

There is a reason why they're used in some aspects in concrete forming structures.

[@theorenhobart]

@@timothychung4811 oooh but it must be secret because you don't explain it ?

[@pwblackmore]

Thankyou for this info - well-presented and informative. You are building for the future, not just to look good. I was working with a colleague when the Building Inspector approved the basement VB being to the local West Coast Canada code. When the BI left, my buddy cut the VB with a huge X, top to bottom - because, as he posited, the moisture would be retained within the stud bays... "Gotta let the walls breathe". I adopted that, but I really should have seen something like this video first. Remember, the code is the minimum... always improve on it. This video explains the best ways. I see you advise EPS, but it has its hazards - off-gassing, and combustibility in particular

[@rosegold7975]

Very informative. Was always unsure about building basement walls the best way

[@jakesaari7652]

Love all the graphics and clear information

[@camelface1]

Great uploads. Love the raw data.

[@ASIRIDesigns]

Thanks so much, glad the videos have been helpful!

[@jacobbeckstrand6764]

Great info! I have the original blueprints for my 1960 built walk out basement house. I'll be doing a remodel in the next few years and suspect I'll reach out to you for the best way to go about insulating the remodel. I like the way you think. I live in Vancouver Washington and like that you are local

[@davidjames4915]

We have a basement built using PWF - permanent wood foundation. Amongst other requirements was that there be granular drainage on the outside of the foundation walls, which continues on underneath the walls and the floor, then is tied into a sump pump. Our basement has never been anything but bone dry... it's probably the driest space in the house. I can't say I've ever truly understood why concrete foundation walls are allowed to just be backfilled with whatever soil came out rather than requiring drainage.

[@larion3296]

Here in Sweden we are primarily installing permeable variants of basement insulation and drainage systems, such as Isodrän. They have probably been dominating for the last 15 years. The insulation is installed on the outside without any membrane. With gravel and drainage tubes below the basement walls. The idea is that the basement walls dry out from the inside, which requires a heated space, and causes a high humidity during the first months. With too high water table some membrane might be needed on the outside of the insulation.

[@PonkyKong]

They build a water proof concrete bottomed box.

[@johnburns2940]

Beautiful!! I was sceptical at first, but all that you detailed follows all that I know and makes Perfect logical/scientific sense. You have just upped my game. I'm in and subscribed! Thank you. Ps, just by default, I installed riding sheet foam on my basement walls, YAY!

[@ASIRIDesigns]

Glad it was helpful!

[@danielfortin5920]

Insulation on the exterior wall. Simple and super effective ! The saturation point (dew point) won't be in the basement, but outside.

[@SharpRealEstateGroup]

👍🏻👍🏻 thank you, very good info!

[@SnakeHandler-g7u]

Do you design residential buildings, or have a catalog I could look at purchasing plans from?

[@kanento]

I have been thinking this for years as the basement walls would have moisture and you had the pink insulation it would get wet and not be able to breath with the vapor barrier. I found this was the case when I purchased another home build in 1950 with a reno in the basement. I noticed drywall was soft so I knew it was getting wet even with the barrier. I have to tear it all out and do foam board first

[@bluearcherx]

i assume this is for new builds with appropriate exterior water management and not for 84 year old basements

[@ASIRIDesigns]

That's exactly right. To address older existing basements, check out this other video on the channel: kzbin.info/www/bejne/gp6comuOZ7Fnbasfeature=shared

[@ConstructionKronies]

Excellent explanation thank you!

[@zuck759]

so if you are building an ICF basement should you tape seems in foam blocks

[@multipotentialite]

What do you recommend for a wood foundation with polyethylene which is not a perfect air barrier (overlapped and stapled instead of taped, gaps near receptacles, etc)?

[@rogiervantilburg3440]

Thanks for sharing!

[@joecan]

Thinking back (24+ years ago), my builder used metal studs with pink insulation and vapour barrier from floor to ceiling in the whole basement. 7 years later, I finished the basement ( added some interior walls and electrical around the perimeter, so i had to cut the barrier to feed some electrical around the basement walls. I didn't notice any mold. This video makes though. Should I bust open a section to check, or just leave well enough alone?

[@jdawes4403]

Thanks Sharif!

[@NaturesInfiniteWELLth-fo6rs]

I recommend considering hemp fiber insulation alongside mineral wool…(one brand rockwool), with similar qualities/benefits. I am planning to build a hempcrete home and will use the hemp fibre bats in the ceiling and crawlspace. :)

[@Langhorstiness]

hemp is organic and organic means it can turn into food for mold. All you need is some vapor condensation inside the hemp and you've just built a really expensive mold farm by accident. I don't think it sounds like the right application for hemp fiber insulation.

[@smallcrush3]

I do have a vapor barrier in mine. But its applied right on the concrete wall, stops at about 2 ft from the floor. The studs are applied on the vapor barrier, which means the plastic film is squeezed between the studs and the concrete wall. There's also isolating foam panels which go from the ceiling to about 2ft from the floor. Dunno if that's desirable or not. No mold though, like at all, unless its deeply hidden behind the drywall... sure hope not!

[@johnwhite2576]

I think you also need to do a video on exterior foundation insulation in this context….other than the issue of deterioration/bugs, it is another viable approach yes?

[@ASIRIDesigns]

Absolutely, if you can protect the exterior insulation from bugs and moisture, it works great. The problem is that this can get complicated depending on what type of rigid insulation you're using. Rigid foams installed on the exterior of the foundation walls have to be treated like ICF foundations, with a fully adhered membrane bonded to the rigid foam, and even that can pose compatibility issues with the adhesives. Rockwool works but you need thick layers and a protection course. For durability reasons I very much prefer installing the insulation on the interior for below grade walls. You can also locate it interstitially, as in the case of a "sandwich" panel, and that works great as well since the insulation is protected.

[@CommieCat]

This is quickly becoming ym favorite channel for building science. I hope you keep on keeping on. I like being an educated GC.

[@peterfroese8606]

at 2:56 you talk about 'the right ratio' between the ridgid foam applied to the concrete wall vs the fiberous batts installed interior of that foam. I've read up on the ratios required for main floor walls, is this the similar ratio you are basis this off of, or is there a similar table where this can be looked up by climate zone? Thanks

[@jamesroscoe7555]

The vapour barrier should be located where it will always be at a temperature above the dew point. Determine the worst case dew point for your climate for all seasons. The foam thickness to permeable insulation thickness ratio needs to be greater than the ratio of the dew point within the indoor - outdoor temperature delta. Note that the outdoor temperature below grade is different than above.

[@richpollock383]

Can you comment on using Zypex concrete waterproofing. I understand it promotes crystal growth into the concrete, sealing it, the product reacts to water infiltration.

[@Langhorstiness]

Xypex is a liquid water crack sealer. It does not block transmission of air and/or water vapor. It would make no different for vapor moving through the concrete toward your vapor barrier.

[@paulstewart2444]

Why does are building code here in Manitoba,Canada require it then???

[@joeltaron1950]

Good question, I’m assuming many places have it as code. I’ve ripped out many basement walls in Winnipeg and found mold and rotten studs behind the poly. I think it has more to do with the quality of the foundation walls and damp proofing on the outside of the walls letting moisture in. Just my opinion on what I’ve seen in this area

[@elbuggo]

Even more better IMO would be to install Pordrän or Isodrän on the outside basement wall!

[@michaelriebandt6754]

New Construction foundation concrete floor has visqueen (plastic sheeting) placed on floor before poring concrete and walls are of foundation have thick layer of more visqueen wrapped around outside walls sometimes repeating the steps. That is Building code (for decades) where I live also keeps moisture from entering past visqueen, Tar may not be enough.

[@multipotentialite]

Don't you also need to have an air barrier around the joists when you use rigid foam?

[@kylejones4149]

Inspector in my area makes us valor barrier even with the foam board behind the framing

[@WalkerEnns]

How do you feel about insulated concrete forms? Based off the information in this video of having a couple inches of Styrofoam to prevent moisture/mold issues and still allowing the wall system to dry this seems like an ideal method of constructing not only basements but above ground as well.

[@ASIRIDesigns]

ICFs are a good system but they aren't a panacea. As I was telling another person in the comments, ICFs absolutely must be protected from water infiltration and insect damage with a fully adhered membrane, but it gets complicated because the membrane and the adhesives have to be compatible with the EPS foam, otherwise things like solvent based adhesives dissolve the foam. Any system can be made to work as long as the the foundation is well drained and the layers are in the right location. That's the key.

[@greatitbroke]

If its in the building code you have to install it to pass the building permit inspections. So whats your answer to that?

[@daijoubu4529]

Rip it off after the inspector pass lol

[@ASIRIDesigns]

You can use a smart vapor retarder instead of polyethylene to allow for drying if conditions get wet. It's allowed by code.

[@lulutileguy]

what about off gassing?

[@pcatful]

Did you say rigid foam IS a class II vapor retarder or rigid foam WITH a class II vapor retarder? 2:35.

[@ASIRIDesigns]

Unfaced rigid foam itself IS a Class II vapor retarder

[@Borisvanderoost]

How about insulating it from the exterior side? Wouldn't that be simpler if it were a new build?

[@frankrizzo2157]

my unfinished old basement was leaky damp dried out quickly

[@FrankandaTrailer]

Question. What about rigid foam exterior. Below grade. Applies over a proper waterproofing membrane applied directly to exterior concrete foundation. Foam is sealed onto exterior as well. Then the foundation is allowed to breath and dry out properly for a couple of years. Then, finish basement. No vapour barrier. I’m not an engineer. I’m asking a question. What is the best most effective method of having a finished basement.

[@ASIRIDesigns]

@@FrankandaTrailer That works well, but only if you're able to keep the rigid insulation dry and away from ants and termites (easier said than done). Ants love to burrow into foam, especially damp or wet foam, and so from a durability standpoint my preference is to locate that insulation layer on the interior.

[@theok4712]

There's technique for insulating basements with house wrap on the concrete block side first then studs, batt insulation and vapour barrier. What are you thoughts on this method?

[@ASIRIDesigns]

It's the same problem.

[@blehssed]

@ASIRIDesigns disagree, it's not a problem on a properly poured and damproofed foundation wall

[@theok4712]

@blehssed how about a block wall built in the 1970's. It's probably not damproofed properly.

[@harrywood8196]

Ive been questioning this for many years. Concrete walls could sweat and therefore a plastic barrier would not let the insulated wall breathe behind the drywall

[@birdologytr3556]

If you buy a new home save money on the initial purchase by leaving your basement undeveloped this will give you a chance to see what state your foundation walls are in by the end of construction.. seen some pretty large cracks in the past that just get covered up . If you have walls that are not in the mechanical room covered up and the rest are bare I would tear that out to make sure the builder wasn't trying to hide something... Just a friendly tip..

[@WANDERER0070]

Even better move is put Rigid foam board on the OUTSIDE basement walls ❤ all the way down to the frost line.

[@mynameIan]

Please note that if the resin used on mineral wool is organic, mould will proliferate on that resin, conditions permitting.

[@vancegosselin]

Mold food, yum

[@MrFredscrap]

Couldnt you cast the basement wall with waterproof concrete mix (ie: materproof admixture)? that should address half of the problem with moisutre coming in from the outside.

[@ASIRIDesigns]

You can, but here's the thing... All concrete cracks. Cracks are pathways for water to enter via hydrostatic pressure. So a drained system is the only way to prevent bulk water from getting inside. As for the other capillary forces and interior vapor drive/air leakage, they need to be addressed accordingly.

[@sorenjensen3863]

Or, do all foundations with icf

[@jeil5676]

I dont think I have any type of vapour barrier on my basement walls. Doesnt seem to have been a problem yet. house built in 60's.

[@glennhiggs11]

HRV!!!!!

[@hoildayfish5032]

I don’t do building or anything connected, cool vid but like why did i even watch it XD

[@evalangley3985]

I am right now searching how to limit radon getting inside my basement from the joint of my basement slab and basement walls. Those foam panels are unfortunately a chimney letting radon inside my basement. I don't know how to tackle the problem.

[@ASIRIDesigns]

To address radon you need to do two things: Keep the radon out by ensuring that you're providing an adequate air barrier at the pressure boundary between the foundation and the conditioned space, and a means of radon removal, which is usually a passive or active subslab depressurization system. You don't want your home to be negatively pressurized, otherwise you're sucking soil gasses into the house. The house should be pressure balanced, or slightly positively pressurized in this case.

[@robertalkemade989]

ridgid foam

[@johnq2068]

That’s what I did, all of it

[@ickster23]

Avoid basements and crawl spaces of you can...

[@marklundeberg7006]

Why is soil at 100% humidity? Sounds like drainage issues.

[@ASIRIDesigns]

Believe it or not, even "dry" soils are somewhat damp! You almost never have bone-dry soils except in extreme climates. Also consider that there is substantially less volume of air in soils, so the small amount of air that is inbetween the tiny gaps of soil particles aren't able to store much moisture in the first place.

[@marklundeberg7006]

@@ASIRIDesigns Interesting, yes reading around I see that even very slightly damp soil can have quite high humidity like 90+%.

[@marklundeberg7006]

​@@ASIRIDesigns Ok I just stuck a hygrometer into a hole in the bottom of my foundation... I'm in a dry climate and I have no drainage issues, it's apparently bone dry crushed rock down there yet 98% humidity... Hah! The basement walls are insulated and barriered in the way you discourage. Unfortunately they are fully finished too... So I can't easily get the hygrometer into the walls.

[@francoisbouvier7861]

Wo, wo. That one picture shows the back side of a shower/ tub situation. That's always a no no.

[@dbdouglas]

Put the framing a half inch or so away from the concrete walls. Put fiberglass insulation in, with paper-backing already on. Then stapled clear, plastic vapor-barrier to the framed walls - but only to the below grade height (of the outside dirt). 30 years & counting with zero problems.

[@robertt9342]

Wouldn’t that create a tone of air and moisture penetration?

[@dbdouglas]

@@robertt9342 In the summer, we have a little de-humidifier on, like we did even before finishing the basement. No problems here, knocking on wood!

[@AspRunescape]

Ive always framed basement walls about an inch off the foundation, then insulated and vapour barriered the wall frame. It leaves enough space for the concrete to breathe behind the insulated wall. Ive never had a problem, but ive also never ripped a wall apart that ive done this way.

[@frankrizzo5958]

Spray foam all the concrete in 2-3 inches of closed cell 2 pound foam and spray foam the rim joist areas as well

[@thegrantdanielsband]

What about house wrap first against the concrete wall then studs then insulation then vapor barrier Then drywall? House wrap sheds water one way but breathes the other way so needs to be installed just like you would on the sheathing on the main floors Staple it to the plates at the top first to hold it up 🙂

[@ASIRIDesigns]

@@thegrantdanielsband No. Watch my latest Q&A where I address this: kzbin.info/www/bejne/b6rSeHmOlJaaoLMfeature=shared

[@bwillan]

If your foundation was built with ICFs you won't have this problem. I am surprised that ICFs are not more commonly used for foundations.

[@adamdawidziuk3267]

As a European it's amazing to see how you heroically fight problems that you yourselves have created. Water bariers/insulation shall be done on the outside, yet I constantly see highly praised new constructions where the same errors are repeated over and over again. You pour concrete into the ground with soil on one side and basement on the other. Seriously ? And then heroically fight problems created by that "design". Frankly I dont know what to call it, some kind of mass -blindness ? Builders' conspiracy to make things bad by design so someone will have to go back and fix it forever ? Hard to say, but funny to watch nontheless. On that note I agree with your observations about this whole internal insulation thing - but this should be done exclusively only when there are no other options. Certainly not with new developments. Please, if you have the power, fix it! :)

[@iancormie9916]

Depends on the climate and nothing else. If you are in the south, where inside temperatures are below ambient ground temp then the vapor barrier must be outside or you must allow the wall to breath to the inside. If you. Are in Canada where the inside is always warmer than outside, then the vapor barrier must be inside. You must never however, put a vapor barrier on both sides of the wall.

[@joe-hp4nk]

What did he say?

[@hotfudgemoney]

Love this channel

[@allantulli5546]

The proper approach is to seal the outside of the basement not the inside.

[@Vertilgen]

Video shows cold going straight through insulation to reach the vapor barrier. Just use better insulation!

[@ASIRIDesigns]

"Cold" doesn't come inside, heat flow is from warm to cold. You need the benefits of an air barrier and vapor retarder in the insulation specs, or find another means of controlling condensation.

[@blehssed]

There's supposed to be an air barrier placed on the concrete prior to insulation. Arguably, the only time this may be correct would be when installing on freshly poured concrete.

[@elcrypto3623]

House wrap with writing facing concrete,then framing,insulation and vapour barrier..standard practice in Canada.

[@ASIRIDesigns]

@@elcrypto3623 This approach is wrong for the very reasons outlined in the video. Vapor barriers trap moisture in the framed cavity... Moisture can and will get inside, either from interior air leakage, inwardly driven vapor diffusing out of the concrete, or from bulk water leaks. That moisure must have the ability to dry out of the moisture sensitive framing.

[@rswow]

Seems like critical info. Please provide a version without the incessant music, else I'm driven away and missing out.

[@acreguy3156]

Agreed. So many YT video producers feel the need to add a background music track. It serves no purpose but to make the producer feel like a real Hollywood pro. The irony is, a REAL pros would NOT use music in such a video. Otherwise, great video!!

[@durwardsaar6000]

I'd tell you to go back to trade school.

[@MrItalianfighter1]

We wear rain coats on the exterior of our body, not on the inside. We should be insulating, water, air sealing the exterior of the foundations as well as the exterior of the house. To be honest, we shouldn't build our homes out of anything like papers or wood.

[@jetterbenne2578]

Finished basements are not a good idea to begin with. There is this obsession of having a basement, finishing it and using it as a living space. it's just a ticking time bomb for disaster.

[@adamford518]

Not everyone has the luxury. Homes are expensive and space is limited so people have to make the best with what they have. Basements are common because the area is dug out for the foundation, so may as well make the best of unoptimal space.

[@jetterbenne2578]

@@adamford518 Sure it is cheaper but in most countries basements are for the pipes, storing wines, and roots.

[@deletesoon70]

Given this overheated real estate racket we are dealing with, maximizing utility and minimizing waste has been forced into people. For some reason.

[@13Mappy]

Completely disagree.

[@HuFlungDung2]

I agree completely. A basement is just waiting for a flood event to happen, sooner or later. Naked concrete is easily washed up after a flood. A basement serves as easy access to the plumbing and heating systems,which inevitably fail and need repairs. That being said, my basement walls were styrofoam concrete forms, inside and out, so it can be heated when needed.

[@artemirrlazaris7406]

Foam... flammable.... Pink insulation styrofoam... flammable... Fibreglass stillnumber one....