# Basement insulation, confusing



## Nealtw (Jun 22, 2017)

If the basement is always cooler than up stairs, with the same air for both the humidity will be higher in the basement. 
Depending on where you live the foam board my be required, we just insulate the 2x4 wall in the Lower Mainland In BC.
Do you know about fire stop needed at the top of the wall. Always the first thing to do.


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## chandler48 (Jun 5, 2017)

Tyvek is normally an exterior wall Weather Resistive Barrier, and is not used inside. Roxul is a good choice as it is waterproof, fireproof, moldproof, verminproof and needs no vapor barrier. Your XPS will give you a sufficient thermal break from the outside temperatures. Not sure why you will employ Sonopan against a concrete wall. You won't have much sound transmitted there.


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## Dusty53 (Jun 28, 2021)

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## Dusty53 (Jun 28, 2021)

Deleted


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## Dusty53 (Jun 28, 2021)

chandler48 said:


> Tyvek is normally an exterior wall Weather Resistive Barrier, and is not used inside. Roxul is a good choice as it is waterproof, fireproof, moldproof, verminproof and needs no vapor barrier. Your XPS will give you a sufficient thermal break from the outside temperatures. Not sure why you will employ Sonopan against a concrete wall. You won't have much sound transmitted there.


I'm thinking the sono pan will help absorb noises that happen in the room, which should make for an overall quieter house. Sure it's against the concrete wall but concrete vibrates pretty good and I think it should help prevent sound from going upstairs, am I wrong to think that?


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## Dusty53 (Jun 28, 2021)

Nealtw said:


> If the basement is always cooler than up stairs, with the same air for both the humidity will be higher in the basement.
> Depending on where you live the foam board my be required, we just insulate the 2x4 wall in the Lower Mainland In BC.
> Do you know about fire stop needed at the top of the wall. Always the first thing to do.


Thanks for the tip about fire blocking... I don't think it's required in my area as none of the people posting videos in my local area talk at all about it... But I'm definitely going to make sure thanks!


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## Dusty53 (Jun 28, 2021)

Any idea if I need a vapor barrier at all? I'm used to seeing a vapor barrier as the last layer before you put on the drywall. I think the XPS makes this pointless but I'm not sure.


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## jim_bee (Feb 23, 2021)

Install the foam insulation to the concrete and tape the joints. Then frame your wall and install the Roxul. Install your drywall. The foam will be your moisture barrier. Don't install another vapor barrier--it's not necessary and may cause problems (mold).


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## CodeMatters (Aug 16, 2017)

Another thread:








Basement Insulation Ontario


I don't have a current insulation project. Just trying to better understand the insulation method I see most often. Guess the point of this thread is to share what (little) I know and get alternative explanations for the techniques I've seen. No doubt this method is described in the OBC...




www.diychatroom.com


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## Nealtw (Jun 22, 2017)

Dusty53 said:


> Any idea if I need a vapor barrier at all? I'm used to seeing a vapor barrier as the last layer before you put on the drywall. I think the XPS makes this pointless but I'm not sure.





jim_bee said:


> Install the foam insulation to the concrete and tape the joints. Then frame your wall and install the Roxul. Install your drywall. The foam will be your moisture barrier. Don't install another vapor barrier--it's not necessary and may cause problems (mold).


Mold is caused when warm moist air comes in contact with colder surface. Fire stop at the top of the wall is also an air stop that is required any where. 
Mold can grow on the surface of the wall when insulation is fitted poorly and cold can get to the back surface of the drywall and condensation forms on the face. 
Mold can grow in a wall when warm moist dirty air leaks into the wall can get passed the insulation and deposits dirt and moisture on a cooler surface. 

When people say 2 VBs are bad. I will ask why. I have yet to understand that.


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## Dusty53 (Jun 28, 2021)

Oh, I live in southern Ontario. I wish more YouTubers would point out where they work since the standards are certainly not the same over north america.


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## Nealtw (Jun 22, 2017)

Dusty53 said:


> Oh, I live in southern Ontario. I wish more YouTubers would point out where they work since the standards are certainly not the same over north america.


Ontario. 
A Good Way To Insulate Your Basement Walls - YouTube

To pass inspect here we have to use one of the wood products talked about here. So check with inspectors for what they want. They have the only opinion that counts.
Fireblocking and Draft Stopping - YouTube


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## CodeMatters (Aug 16, 2017)

Nealtw said:


> When people say 2 VBs are bad. I will ask why. I have yet to understand that.


I'd always heard that too (that 2 VB's are bad). Then I wired a couple places that 
were electrically heated and discovered that the OBC required electrically heated
residences to have additional insulation, and an accepted method was 2" of taped 
styrofoam on the outside of the cladding. Regular 6mil poly VB still required inside. 
So apparently the OBC does not have an issue with 2 VB's, and even requires it in 
at least one situation.


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## Nealtw (Jun 22, 2017)

CodeMatters said:


> I'd always heard that too (that 2 VB's are bad). Then I wired a couple places that
> were electrically heated and discovered that the OBC required electrically heated
> residences to have additional insulation, and an accepted method was 2" of taped
> styrofoam on the outside of the cladding. Regular 6mil poly VB still required inside.
> ...


Yet people repeat it constantly but can never explain it. The moisture level that is in the lumber is not high enough to support mold and if you cut off the air supply that also stops mold.


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## jim_bee (Feb 23, 2021)

I think the issue is that the vapor barriers are not 100%. Even 2" of XPS is semi-permable and will allow moisture in the concrete to migrate to the interior. If you then put another vapor barrier on the inside, sandwiching the framing and insulation between two barriers, there is an opportunity for enough moisture to accumulate to support mold growth. 

Note that the website in the first posting suggests three methods of framing & insulating a basement wall. One is to use poly moisture barrier against the masonry, but all three provide for the framing and insulation to "breath" to the inside. There is some good information at the Building Science website. Frankly, I wasn't easily convinced, but the more I've read, the more I think they are correct. On the other hand, I've never had the opportunity to take apart a basement wall built to those specs to see what happened over time.


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## Dusty53 (Jun 28, 2021)

I've done some more digging, my questions arise due to this article:





Keeping The Heat In - Section 6: Basement insulation: floors, walls and crawl spaces







www.nrcan.gc.ca




saying:

*Finishing*
Install a vapour barrier over the studs and insulation. In basements that have proven to be dry, a polyethylene vapour barrier is suitable. However, if you have any doubts or there is a risk of dampness in the basement, there are two alternate methods that may be better suited.
The first alternate method is to use polyamide sheeting, a breathable membrane also known as Nylon-6 vapour retarder film or smart barrier. When installed on the warm side of an exterior wall, smart barrier has a water vapour permeance that changes with the conditions within the wall. If the relative humidity in the wall cavity increases, the smart barrier will allow the wall to dry out toward the interior unlike other sheet-type vapour barriers. If you are using smart barrier, carefully follow manufacturer’s directions and installation requirements, though its application is similar to polyethylene sheet with a few important exceptions.

So what on earth is a Nylon-6 vapour retarder film and how is it different from a vapour barrier? I finally found this product:


https://castle.ca/product/membrain-9-4-CIC57135/



So it seems it actually exists! Though I can't find anywhere to actually buy it.... the search continues it seems.


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## 3onthetree (Dec 7, 2018)

Vapor retarders will let a certain size water molecule pass through based on its perm rating. If you have 2 sandwiching a space some molecules will pass through 1 film into this space. If the temperature between the opposite sides of the space are not consistent, then a molecule might combine with others, enlarging itself and not being able to pass through the 2nd film. This is how Tyvek works, small molecules on the interior face can pass through, but larger molecules on the outside face (usually water drops at that point) can not fit through.


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## SLSTech (Jan 19, 2021)

The issue with 2 vapor barriers is creating a moisture sandwich - at least that's most peoples worry. With that as pointed out there are numerous times we create them & they are acceptable - for example, a hot roof assembly (done properly with CC Foam). The biggest thing is if you do create a sandwich is to get your details bang on so water / vapor does not get into that area aka no issues. But as a general rule, don't create them unless you know what you are doing & can do it right.


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