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Basement insulation and vapor barrier

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Deal Expert
Oct 20, 2001
18709 posts
1157 upvotes

Basement insulation and vapor barrier

When we got our house from the builder 7 years ago, the builder had installed pink fiberglass insulation half way down the wall of the basement. There's a vapor barrier on the 'warm' side and no moisture barrier on the concrete side. And we have 'waffle board' on the outside of the foundation, coming up to a couple inches above grade. We've never had any leaking or moisture problems down there.

We're now finishing our basement and we're going to install insulation (Roxul Flexibatt) to the floor. But we already finished the framing before fully looking into the moisture barrier and vapor barrier requirements (doh!). So here's the situation: we've got the studs out at least 1" from the foundation wall (more than that in most places), with a layer of 6 mil poly attached between the framing and the pink insulation. Is this okay, or do we need to do something about the lack of moisture barrier behind the existing insulation? The poly that we added goes up to the top plate...is that too far up?

Also, we've got a wall between the main area of the basement and the furnace area. We're using 2x6's for that wall, and we'll put Roxul Safe 'n' Sound for insulation there. Do we also need vapor barriers on either of the sides of that wall?
These folks have taken over RFD, so I'm done here.

Mutu qabla an tamutu
12 replies
Deal Addict
Mar 21, 2006
4149 posts
267 upvotes
Burlington, Ontario
I'm doing the same thing (basement was already finished, but without insulation).

Up against the cinder block foundation I put 1" styrofoam, then studs, then pink insulation between the studs, then vapour barrier. Hopefully you put the poly on the ground too where the bottom plates go so the wood does not touch the concrete floor. You wrap that poly up into the vapour barrier so that any future moisture does not come up and rot the wood.

According to my site supers, you leave about 6 inches of space up from the bottom so it can 'breathe' or something.
Sr. Member
Jan 25, 2004
972 posts
Do not put poly between the insulation and the wall. I recommend not to use any poly vapour barrier in a basement studded wall, it causes condensation and eventually dry rot. I recommend to transfer your air barrier to the concrete wall at the rim joist height to maintain a consistent building envelope, and seal the concrete up to the level of the grade outside to help minimize condensation, then frame and insulate as normal and drywall.

People over-emphasize the concept of a vapour barrier....don't worry too much about using poly everywhere, especially in your basement. Chances are whatever you use to create your building envelope....if you cannot blow through it......it is an acceptable air/vapour barrier. If you can stop the escape of air, you are stopping the escape of humid air which causes problems. After building many houses using R2000 specs and the ADA (Airtight Drywall Approach) I have a pretty decent understanding of these things.
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Heatware ID SledBC
[OP]
Deal Expert
Oct 20, 2001
18709 posts
1157 upvotes
sledbc wrote:
Jul 2nd, 2007 12:49 pm
Do not put poly between the insulation and the wall. I recommend not to use any poly vapour barrier in a basement studded wall, it causes condensation and eventually dry rot. I recommend to transfer your air barrier to the concrete wall at the rim joist height to maintain a consistent building envelope, and seal the concrete up to the level of the grade outside to help minimize condensation, then frame and insulate as normal and drywall.
My father-in-law is a builder in the US and he's been doing most of the work in our basement... and what you describe is his thinking as well. Down there, they have a paper-faced fiberglass insulation with which the paper provides the vapor barrier. (I don't know if the same thing is used up here...?)

But the Ontario Building Code says:
9.25.4.3. Installation of Vapour Barriers

(1) Vapour barriers shall be installed to protect the entire surfaces of thermally insulated wall, ceiling and floor assemblies.

(2) Vapour barriers shall be installed sufficiently close to the warm side of insulation to prevent condensation at design conditions.
So it seems to be required by code here. :?:
These folks have taken over RFD, so I'm done here.

Mutu qabla an tamutu
Deal Addict
Mar 21, 2006
4149 posts
267 upvotes
Burlington, Ontario
I work in a lot of new construction with basements that are being sold finished to EnergyStar compliance.

The have a tar paper up against the concrete foundation, then wood studs 1" out from there, then fill that with white insulation, then 6mil poly then drywall.

Again, they don't fill the bottom 6" with insulation.

Is this the best way? I have no idea. I just know it's what they need to do to get their code and EnergyStar compliance.
Sr. Member
Jan 25, 2004
972 posts
Rehan wrote:
Jul 2nd, 2007 1:05 pm
My father-in-law is a builder in the US and he's been doing most of the work in our basement... and what you describe is his thinking as well. Down there, they have a paper-faced fiberglass insulation with which the paper provides the vapor barrier. (I don't know if the same thing is used up here...?)

But the Ontario Building Code says:

So it seems to be required by code here. :?:
The problem is that even though you're following the rules...concrete absorbs moisture from the ground and trapping that air inbetween your concrete and poly will cause mold/mildew and or dryrot. Alot of people do it the way you describe, but in my experience its just not the best way.
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Heatware ID SledBC
Sr. Member
Jan 25, 2004
972 posts
BuildingHomes wrote:
Jul 2nd, 2007 2:12 pm
I work in a lot of new construction with basements that are being sold finished to EnergyStar compliance.

The have a tar paper up against the concrete foundation, then wood studs 1" out from there, then fill that with white insulation, then 6mil poly then drywall.

Again, they don't fill the bottom 6" with insulation.

Is this the best way? I have no idea. I just know it's what they need to do to get their code and EnergyStar compliance.
Tar paper is good, it will keep the moisture from the concrete off the studs, we just roll dampproofing on the wall up to the level of the ground outside, then insulate the entire wall, put a sill gasket under the bottom wall plate and scrap the vapour barrier. That way any moisture that does end up there will evaporate into the building envelope. There shouldn't be much moisture, but if you put poly there it will capture it and it could, and has in the past been a problem. Really....not having poly vapour barrier in your basement isn't going to cause you any hardship.

I cannot see what leaving the insulation up 6" will do..........wouldnt that just leave a cold space in the coldest part of your home?
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Heatware ID SledBC
Member
Aug 11, 2003
434 posts
7 upvotes
sledbc wrote:
Jul 3rd, 2007 2:57 am
Tar paper is good, it will keep the moisture from the concrete off the studs, we just roll dampproofing on the wall up to the level of the ground outside, then insulate the entire wall, put a sill gasket under the bottom wall plate and scrap the vapour barrier. That way any moisture that does end up there will evaporate into the building envelope. There shouldn't be much moisture, but if you put poly there it will capture it and it could, and has in the past been a problem. Really....not having poly vapour barrier in your basement isn't going to cause you any hardship.

I cannot see what leaving the insulation up 6" will do..........wouldnt that just leave a cold space in the coldest part of your home?
I have been thinking about this same issue for awhile now. We plan on finishing our basement this year. The "traditional" thinking has been to put up the studs, insulate and then install the vapor barrier, similar to how one would finish the upstairs living space. But most basements seem to acquire that musty smell. The exterior walls in the upstairs area can and does breathe to the outside. There should be "no" moisture buildup. Unless of coarse, you have a leaky roof. Once the exterior basement walls gets wet, there is "no" place for the moisture to go. It gets trapped behind the vapor barrior.

There is an article in the March, 2005 edition of Fine Homebuilding, "The Stay-Dry, No-Mold Finished Basement," written by Andy Engel. He recommends a rigid foam insulation (tapped between sheets) on the exterior basement walls. Quote, "Rigid - foam insulation is semipermeable and won't trap moisture ...." He also states that much of his information is obtained from Building Science Corp, website buildingscience.com. (add the www.)

I am not sure what the codes would say in this regard. What Engler and Building Science Corp says makes sense. But I haven't had actual experience with this, nor do I know what will happen when I go for my permits.

In Calgary, we have experienced a number of storms over the last three years. As I understand it, approx 10% of the homes got some water damage. I am not sure about those numbers. But I know some people who experienced minor water seepage through the exterior basement walls. Minor water seepage may not create an immediate problem. But I suspect that it would cause a longer term mould problem.

I would like to hear what Sledbc has to say about this and what his experience has been with the Building Inspectors when he builds "without" using vapor barriers in the basement. Based on my "limited research" and "no" actual experience, eliminating the vapor barrior is the right way to go.

I have read other people saying similar things to Engel and Sledbc. But I can not remember where or give exact quotes.
[OP]
Deal Expert
Oct 20, 2001
18709 posts
1157 upvotes
If the poly moisture barrier is supposed to stop at ground level, then how should it be attached to the concrete? With strapping screwed to the wall using concrete screws? That seems like overkill, so I'm assuming there's something better...?

As I mentioned earlier, we've already got pink fiberglass insulation half way down the basement wall, with a 6 mil poly layer on top of that. And then we added our own layer of poly, which currently goes up all the way to the top plate. The Ontario Building Code says:
9.13.2.6. Interior Dampproofing of Walls

(1) Where a separate interior finish is applied to a concrete or unit masonry wall that is in contact with the soil, or where wood members are placed in contact with such walls for the installation of insulation or finish, the interior surface of the foundation wall below ground level shall be dampproofed.

(2) The dampproofing required in Sentence (1) shall extend from the basement floor and terminate at ground level.

(3) No membrane or coating with a permeance less than 170 ng/(Pa.s.m2) shall be applied to the interior surface of the foundation wall above ground level between the insulation and the foundation wall.
To "fix" this stuff to try to be in accordance with code, we're thinking of cutting off the two layers of poly above ground level. The pink fiberglass above ground level would then be exposed, and it would be covered up by the Roxul insulation we'll be adding between the studs. Would this make sense?
These folks have taken over RFD, so I'm done here.

Mutu qabla an tamutu
Newbie
Mar 30, 2007
23 posts
Oshawa
Rehan wrote:
Jul 3rd, 2007 8:33 pm
If the poly moisture barrier is supposed to stop at ground level, then how should it be attached to the concrete? With strapping screwed to the wall using concrete screws? That seems like overkill, so I'm assuming there's something better...?

As I mentioned earlier, we've already got pink fiberglass insulation half way down the basement wall, with a 6 mil poly layer on top of that. And then we added our own layer of poly, which currently goes up all the way to the top plate. The Ontario Building Code says:
To "fix" this stuff to try to be in accordance with code, we're thinking of cutting off the two layers of poly above ground level. The pink fiberglass above ground level would then be exposed, and it would be covered up by the Roxul insulation we'll be adding between the studs. Would this make sense?
Quote:
9.13.2.6. Interior Dampproofing of Walls

(1) Where a separate interior finish is applied to a concrete or unit masonry wall that is in contact with the soil, or where wood members are placed in contact with such walls for the installation of insulation or finish, the interior surface of the foundation wall below ground level shall be dampproofed.

(2) The dampproofing required in Sentence (1) shall extend from the basement floor and terminate at ground level.

(3) No membrane or coating with a permeance less than 170 ng/(Pa.s.m2) shall be applied to the interior surface of the foundation wall above ground level between the insulation and the foundation wall.

To "fix" this stuff to try to be in accordance with code, we're thinking of cutting off the two layers of poly above ground level. The pink fiberglass above ground level would then be exposed, and it would be covered up by the Roxul insulation we'll be adding between the studs. Would this make sense?



As it states..."No membrane....BETWEEN the insulation and the FOUNDATION wall"...so none BEHIND the insulation on the portion of wall above grade.
Member
Oct 7, 2007
483 posts
16 upvotes
Markham
If you use 2" extruded foam on the walls instead of just the 1", you won't need 6 mil poly since the 2" of foam acts as the vapor barrier.
Newbie
Apr 12, 2006
3 posts
I am currently 80% complete on framing the basement walls. Originally, the basement was halfway insulated by the builder. We removed the original half insulation and built the 2x4 wood framing around. The plan is to then use the R12 batt then 6mm poly to close the framing.

I was told that I need tar paper between the 2x4 wood and the concrete. I should be able to insert the tar paper at this stage.

Do I need the tar paper? How much of the wall do i need to cover? From the top sil all the way down or just from the ground level all the way down or just the top half part?

Also, how would I attach the tar paper to the concrete wall.

Please help...
Member
Mar 28, 2007
267 posts
9 upvotes
Hi ATMPROVIDER

Instead of using tar par...i strongly suggest you using TYPAR...please check out their site...

I used this in my basment , instead of tar paper...it is a bit more expensive then tar paper...

Make sure that the felt portion of typar facing the inside of the room ..

you need glue to apply on the concrete side of all and just paste the typar ..

issy
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