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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[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!

[RatedCfm-czff]

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 90's-early 2000's, 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.

[julibark]

Such an incredibly informative video. I had vapor barrier installed on painted concrete block basement walls about 5 years ago...along with an internal French drain. In less than 6 months, I could see the mold growth "everywhere" behind the barrier. The walls were already painted when I purchased the home and while the basement "felt" pretty dry, I was seeing signs of water infiltration. Fast forward to today, I now have foundation issues. The vapor barrier isn't the cause but if I had come across this video 5 years ago (along with other info I've recently uncovered), I would not have allowed the contractor to put the barrier on the walls. I have clay soil, a yard that grades toward the home and cast iron pipes that act as both a sewer line and storm drain. The pipes need to be replaced (in process now). Also, the side of my house is only 8 feet from my neighbor's driveway retaining wall - and the back of their yard slopes to the back corner of my home. A bit of a perfect storm. The information you share is invaluable.

[justbobsmith]

I agree in theory on your point about not putting vapor barrier on the inside wall in basement but if you do, you will fail building inspection in most provinces in Canada. It's building code to install it that way.

[gnargnar]

Probably the most underrated building engineering channel.

[larion]

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.

[WalnutMountain-kt]

I did my basement years ago. I dug the exterior walls down, installed 2” blue styrofoam down to the footings then went another layer of 2’’ for 2’. Gave me 4” for the frost line. Then i did the interior basement walls with 1” blue top to bottom. Basement is dry and warm. Seems to be okay to this day, i believe its been 25 years and no issues!

[davidjames]

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.

[danielfortin]

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

[viktoreisfeld]

Great job on this video! Just had to "un-finish" a finished basement that had massive black mold due to plastic vapor barriers. I think it's insane to finish a basement in anywhere other than a desert. Digging up the ground to pour the foundation and run off from the roof means basements will always be damp/humid... perfect for mold. I would never build a home with a basement or finish a basement. You're better off with an above ground addition, if you're already stuck with a basement - cheaper in the long run.

[birdologytr]

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..

[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

[EJ.Quarry.Dweller]

Used pink panther foam against the concrete block and then used a pvc bottom plate for the 2x4 walls. It has worked out really well we also keep a eye on moisture content of our basement air and run a dehumidifier in the moist months have had many comfortable years in the basement rooms. Lived in the house for a few years monitoring the Block walls We live on a hill above town and all the landscape around the house pitches away nicely and I added Gutters for extra water control. Made sure to have no major leaks before attempting framing and drywall. Good luck to any one upgrading living space.

[bluearcherx]

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

[johnburns]

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!

[zalllon]

Glad I saw this video before starting on my basement. I have a 2017 build home just outside Toronto, and was initially going to leave up the builders vapour barrier on the concrete wall that surrounds the Earth under the garage floor. But I’ll definitelyuse the rigid foam approach and then frame on top of that.

[Universal.G]

Forget spray foam. People have had to tear their house apart after getting it sprayed. The manufacturing process happens in your house. If the chemicals don't mix right, you will have a health hazard right in your house.

[Magmaa]

Im renovating our basement now, the wall framing and insulation is dry and no mold at all. And thats with a vapor barrier.
The floor had vapor barrier on the concrete, then 5cm insulation. A lot of water there, so we're doing 10cm xps, then vapor barrier, then 5cm xps with concrete on top. That'll fix the floor issues.

But should i put vapour barrier on the walls as well then since its worked fine in the existing walls for 40 years? We're putting up wooden panels again, since it's better than drywall in moist enviroments. Only difference is that we wont put up the black paper stuff behind the wood. just a 2cm air gap with a thick layer of asphalt stuff under the wood so its not in direct contact with the concrete.

[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

[jacobbeckstrand]

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