Basement vapor barrier

Where would plastic vapor barrier go on a finished basement wall? After much researching, I’m getting mixed responses. Would it go on the studs right under drywall (as seen in pic) or go on the concrete wall (then studs & drywall)???

NW Ohio (cold climate)

Hi Joshua,

I think the vapor barrier goes on the wintertime warm side of the insulation, so vapor barrier, insulation then foundation. The vapor barrier will help keep continuous contact between insulation and concrete.

Another method is 2" of extruded poly. directly on the concrete and then your interior finish.

Check out this link. It’s a good read for cold climate basements.


Quote: From Moisture Intrusion 2.4.3

**Understand How Basement Insulation and Finishes Should Dry to the Interior **

Low permeability and continuous vapor retarders, like polyethylene sheeting or vinyl wall paper, on the interior side of basement finishes should be avoided because they will tend to trap moisture vapor moving through the foundation wall and slow the drying process for new foundations. Therefore, unfaced fiberglass batt insulation and permeable paint finishes on gypsum wallboard should be preferred on basement finished wall assemblies. Other proprietary basement finish systems, using products such as rigid fiberglass insulating boards, have also performed well in testing and use. However, use of certified installers may be required by the manufacturer

A vapor barrier on the basement walls is an important part of finishing your basement.
First it will protect any water leaks from wall ties, or wall cracks (even ones that have not occurred yet).
Second, wall vapor barriers provides your finished basement a moisture barrier to help keep high humidity, condensation, and vapor transmisson under control.
Wall vapor barriers should be at least 6 mil thick.
When using a wall vapor barrier remember to use unfaced insulation so as not to trap moisture between the vapor barrier and the insulation.
The wall vapor barrier should be installed on the foundation wall and tucked into any perimeter drainage system that is installed.

Your basement walls could than be installed in front of this vapor barrier and then insulated using unfaced battings.
Over the last40 years of waterproofing basements, I have seen too many homeowners and contractors refinish a basement without installing a proper wall vapor barrier.
If you are planning on having your basement waterproofed usually the Basement Waterproofing Contractor will install a vapor barrier upon request when installing the sub floor drainage system.
If you are having your basement refinished, make sure the you contractor installs a wall vapor barrier before building your basement walls.

Hope this helps a little.

Marcel :):smiley:

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Does this include exterior water proofed foundations or just exterior damp proofed foundations? Is a retarder, not barrier, internally installed on exterior waterproofed foundations acceptable or correct?

Carl :neutral:

I would think that since most residential foundations executed by the residential market contractors have no idea how to waterproof a foundation that I have seen in my area, the same would apply for elsewhere.

The assumption at this stage would be that it is dampproofed at the very most.

The ideal situation in a basement insulation would be to use z-girts and 2" Formula 150 extruded polystyrene insulation where no air space is required nor a vapor barrier to trap moisture between the insulation and the concrete wall.

As I posted, the moisture of the concrete coming from the exterior and concrete itself, is enough to create a problem.

Now if a water proofing membrane is installed at the exterior foundation, the sceniaro changes. Most of the water proofing membranes are also low perm rated materials and will stop most of the moisture vapor through the assembly.
Therefore creating a very dry basement interior.

I have one of those myself. I would not apply any vapor barrier in my basement.

There are a lot of pros and cons on this subject, I only speak of what I have seen and works.

Marcel :):smiley:

Oops, I guess I’m mistaken then. Sorry about that Joshua (but pleased to learn something!).

Marcel, I have a dampproofed basement, concrete block construction, no insulation. I was planning on adding 2" of extruded polysterene directly to the walls for both thermal break and vapour barrier, and properly sealing all seams. Then, my studs and drywall. Any thoughts?



Hi. Paul-Marc;

Now this is one French name to another I believe. ha. ha.

I found this for you to support somewhat what I was saying.

How To Insulate Basement Walls

Insulating Basement Walls

Insulating a basement properly is rather challenging in cold climates. In this post I’d like to discuss how to insulate basement walls in cold climates.
Insulating basement walls in cold climates is a great way to keep your home warmer and drier. However, special care should be used when insulating concrete basement walls. Below grade concrete foundation walls are very cool and damp. If you were to insulate the walls with regular fiberglass batt insulation it is very likely that a mold problem would develop. I like to use a combination of products to insulate basement walls. In order to create a vapor barrier and separation between the concrete walls and wood framing I like to use extruded polystyrene insulation (blue board from DOW). Next we frame a traditional wood stud wall in front of the polystyrene insulation. We do take one special step in framing the wall. First we install a layer of composite decking between the concrete slab and the pressure treated bottom plate of the wall. Finally we install some type of insulation in the wall cavities.
Step 1 - Install Extrude Polystyrene Insulation Boards

The first step in insulating a basement wall is to install the polystyrene insulation. We like to use a all purpose adhesive that’s approved for Styrofoam products. After the polystyrene insulation is installed each of the joints is taped with Tyvek tape or some other approved tape that adheres to polystyrene insulation. By taping the joints you are helping keep moisture and cold air from infiltrating into the stud wall cavity.
Step 2 - Frame Basement Wall the basement walls is very straight forward. Use traditional wall framing techniques with two slight modifications. First I recommend installing a piece of composite decking (Trex, TimberTech, etc.) on the slab (use a Powder Actuated Tool to shoot the decking into the slab) below where the wall bottom plate will rest. By installing a piece of composite decking (see arrow in photo) you will ensure that water does not “wick” up into the wall should there ever be any water leaks in the basement. Next just frame the wall with a pressure treated bottom plate and stand it up. Nail the top plate into the first floor joists and then nail the bottom plate into the composite decking. Be sure to plumb the wall with a builders level.
Step 3 - Insulate Stud Wall Cavity

Now you’re ready to insulate the stud wall cavity. There are a couple of options here as well. You can insulate the wall with fiberglass insulation, you can use wet sprayed cellulose insulation or you could use spray foam insulation. I insulated my basement walls with fiberglass insulation. For this house we’ll be using wet sprayed cellulose insulation. I’ll be sure to write several posts about the spray applied cellulose insulation when we get to that step of this project.
Step 4 - Finish Wall Surfaces

The final step is installing some type of finished basement wall surface. We’ll be installing normal drywall in this basement. You could certainly use most any material type that you want.
Basement Wall Insulation Summary

Insulating your basement walls will help keep your home warmer and drier. By insulating them properly and creating an effective vapor barrier you’ll be able to reduce the amount of moisture that enters into your basement from the damp moist concrete walls. Concrete is always full of moisture so it’s very important to keep materials like wood and fiberglass insulation away from the concrete surface. By taking the time to properly insulate your basement you’ll be able to enjoy the extra space for years to come with little maintenance.

Word of caution;

I am not a strong advocate of Block Foundation Walls in the Great White North.
Insulating a block wall per details of the above will greatly reduce the amount of heat loss transmition through the wall protecting it from lateral forces from the frozen and heaving of the unbalanced fill on the outside.

Not knowing if this block wall is reinforced properly, I would caution in doing so.

Hope this helps.

Marcel :slight_smile:

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Thanks Marcel for the additional info. The description above is along the lines of what I was thinking. I’ve got plenty room and might lay a 1" layer of the same extruded foam board on the concrete floor to go with the wall insulation, then plywood screwed through that into the floor, and wall framing on that. It will be like a foam box down there.

Thanks again Marcel - merci!


Vous êtes bienvenu mon ami:):smiley:

You need to consider the application[FONT=Tahoma][size=2]. Is the basement being finished as a retrofit or is it new construction.
[/size][/FONT]Hopefully during new construction they will be waterproofing the foundation in preparation for a finished basement. You also have the person building the house handy so you can find out whether it was done or not without digging a hole front yard.
Your picture appears to be new construction[FONT=Tahoma][size=2].
[/size][/FONT]Things that you must consider is what causes condensation.
Condensation occurs when the temperature of the air drops to where the water vapor in the air (relative humidity) reaches a saturation point and condenses.
Building foundations generally have a constant temperature about 50 to 60[FONT=Tahoma][size=2]° depending on your location. If the condition space where to be below the expected foundation wall temperature then you may reconsider placement of the vapor barrier.
[/size][/FONT]Hot always goes to cold[FONT=Tahoma][size=2]. When it does and it is cold enough, condensation will occur.
[/size][/FONT]The majority of the time the outside foundation wall will be cooler than the inside temperature of a finished basement.
Another thing that must be considered is the relative humidity that occurs when you finish the foundation wall. If the foundation wall has not been waterproof[FONT=Tahoma][size=2]ed[/size][/FONT] [FONT=Tahoma][size=2](because it was never intended the finished basement), then the air within the wall space against the foundation will be 100% saturated at almost any temperature. Evaporative cooling could cause condensation to occur even if the indoor temperature is warmer than the foundation wall. In this case you will need a vapor barrier between the finished wall and the foundation.

If you have fiberglass batt insulation on your basement wall and you do not install a vapour barrier on warm side of wall, you will have moisture collecting where ever the warm air hits the dew point (usually in the insulation). Using styrofoam will prevent this problem if properly sealed, but I have seen lots of homes with fiberglass batts used to insulate basement walls in Ontario, some people even put metal studs right against concrete. Thats what make this job so interesting…there is always something new to look at :slight_smile:

How can the topic of finishing a basement wall that’s below grade accommodate for two such drastically different opinions on whether it should be covered with a vapor retarder?

The cost of the vapor retarder is probably significant, as is the cost of a vapor retarder that’s trapping moisture against the basement wall for extended periods of time.

Ben and Nick Gromicko, I think that it’s time that you stepped up and said something on this thread about it, in light of multiple Master Inspectors who are saying that a vapor retarder on the inside of a basement wall below grade is not a defect.

I need to know the one correct answer. Is it a defect or is it not a defect?

This message needs to be consistent among all inspectors, doesn’t it? Otherwise aren’t we practicing something other than being advocates for the best that current building standards and science has to offer?

Internachi training: Basement Walls Dry to the Interior
InterNACHI: Int’l Association of Certified Home Inspectors

Internachi training: No Vapor Barrier
InterNACHI: Int’l Association of Certified Home Inspectors


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While I agree with Marcel and the others re the no vapor barrier on concrete, the local building industry and city inspectors do not agree with me, so I say nothing. Canada/Alberta building code says continuous air barrier (as opposed to vapor barrier) is required. Builders use batts because they are cheaper, the better builders use mineral wool, which can handle getting wet better than fiberglass. The continuous air barrier is cut about 2 inches long on the bottom and not sealed to the slab, that way trapped water is free to run out under the plate or track onto the slab. Foundation walls are damp proofed with bituminous whatever painted on, sometimes on both outside and inside or just outside only. So far so good for most houses.

I inspected a newer house the other day for people who had a wet basement and wanted to know why, interior rh was 50%!! It was about 0 F outside, to make things even worse they removed the insulation from one of the walls, the walls were soaked. The insulators had done a crap job with the air barrier, so the cause was a combination of (mostly) way too high humidity plus an air barrier that wasn’t.