Vapor Barrier on Basement Walls

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WorldExplorer44
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Vapor Barrier on Basement Walls

Post by WorldExplorer44 » Thu Jan 10, 2019 10:19 am

I have an unfinished 1200sq ft basement that is partially below grade. I live in Pennsylvania.

Always been humid in the space but never had any leaks or anything like that through the walls however I used drylock over all the walls just to be sure.

Watching Shannon's video (https://www.youtube.com/watch?v=zDNyjR1SHUQ) I installed rigid foam of 1/2 inch over the concrete block walls. I then installed 2x4 treated lumber framing. Foamed up all the corners and cracks etc. Everything went up smooth.

Now I am on to the batts insulation. This is where I think I might have messed up.

I bought R-13 FACED batts. Just as a test I filled one space with a roll and left it sit for 2 days. Note that I did NOT staple the facing. After 2 days there was a good amount of moisture behind the batts.

Will this moisture be solved by a vapor barrier? Or is there something I need to redo.

Thanks for any and all advice.


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Shannon
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Re: Vapor Barrier on Basement Walls

Post by Shannon » Thu Jan 10, 2019 11:43 am

What is the humidity level in your basement?
During the construction stage it would be common to have some moisture problems until everything is sealed up but if you have excessive moisture it will need to be controlled anyways.
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WorldExplorer44
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Re: Vapor Barrier on Basement Walls

Post by WorldExplorer44 » Thu Jan 10, 2019 2:04 pm

I have two dehumidifiers running 24/7 and it's able to maintain about 55-65%.

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Shannon
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Re: Vapor Barrier on Basement Walls

Post by Shannon » Fri Jan 11, 2019 8:01 am

Hmm that is a fair amount of humidity then. Is this normal for Pennsylvania? What you are keeping it maintained at is even on the high side IMO. I would say 40-50 is best depending on time of year.
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WorldExplorer44
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Re: Vapor Barrier on Basement Walls

Post by WorldExplorer44 » Sun Jan 13, 2019 10:28 pm

I can't say for sure about Pennsylvania in general but pretty much everyone I know that has a basement will have a dehumidifier running. My situation is made worse (I believe) because I have radient floor heat, except in the basement. So there is no forced air like most folks drying out the air in the house.

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Re: Vapor Barrier on Basement Walls

Post by Shannon » Sun Jan 13, 2019 11:04 pm

Here in Saskatchewan finishing basements in winter will usually have moisture in the wall cavities to some extent. But installing the foam reduces the amount because you are really getting rid of the cold concrete surface where warm moist air will turn to condensation.
In your case the 1/2” foam is maybe not enough to make a difference? I use no less then 1” when I do basements. Maybe running a extra dehumidifier during construction would help? We also do not use craft paper as a vapour barrier.
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WorldExplorer44
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Re: Vapor Barrier on Basement Walls

Post by WorldExplorer44 » Mon Jan 14, 2019 9:26 am

I did buy a new dehumidifier since my first post last week and that has helped.

Should I use a vapor barrier? Is it OK to use the faced batts with the vapor barrier over top of that?

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Re: Vapor Barrier on Basement Walls

Post by Shannon » Mon Jan 14, 2019 12:46 pm

Use one or the other ,not both. I’m not sure what is “normal “ in your area for sure . Check with the local lumber suppliers or contractors.
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Re: Vapor Barrier on Basement Walls

Post by Scubasteve » Mon Jan 21, 2019 8:32 am

Shannon wrote:
Mon Jan 14, 2019 12:46 pm
Use one or the other ,not both. I’m not sure what is “normal “ in your area for sure . Check with the local lumber suppliers or contractors.
Hey Shannon, I just wanted to add a couple more factors to the topic. The exact same thing happened to me. Except I used 1” on the concrete walls, and I live in a climate closer to yours( Sudbury, Ont). I understand I should of maybe went with 2”, given that it gives you that thermal break, but 75$ for a sheet was a little tough to swollow. My guess of what is happening is that cold is still making it to the surface of my foam. does this give you a better idea of what’s up?

Thanks!

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Re: Vapor Barrier on Basement Walls

Post by Shannon » Mon Jan 21, 2019 6:41 pm

Over time the foam will be colder then the air inside so excess moisture in the warm moisture air may turn to condensation on contact. Unless its raining down the sheets you need to get things covered up ASAP. If its "raining" you may need to reduce the humidity first.
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GeorgeKez
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Re: Vapor Barrier on Basement Walls

Post by GeorgeKez » Tue Jan 22, 2019 12:40 pm

Hi Shannon, my first post. After reading your posts I am thinking that I should go with 2 inch rigid foam on the basement walls. I have already bought 1 inch Durafoam. Do you see any issues with me doubling up on the foam... aside from me doing double the work? I would stagger the seams, tape and foam the top and bottoms. Then I will go out and buy more 2 inch Durafoam to finish the job. I live in Hamilton near Toronto. Thanks George

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Re: Vapor Barrier on Basement Walls

Post by Shannon » Tue Jan 22, 2019 1:04 pm

Hi George I am not completely familiar with Durafoam. Because I am not I would check with manufactures recommendations and also check your local codes. One thing to check is if Durafoam is considered a air/vapour barrier at either 1" or 2" thick? If so then you would want to avoid using a interior air/vapour barrier under the drywall as you will then trap moisture if it does get inside.
I know that some areas will allow 2" XPS rigid foam is considered a air/vapour barrier but less then that is not. Also your plan of staggering the joints is a good one.
So check your local codes to see what R value you need in the basement as well. If your 1" foam is maybe R4 and you use 3-1/2" Roxul (R-14) in the stud bays you would have R18 and that may be all you need?.

Let us know what you find out for your area.
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GeorgeKez
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Re: Vapor Barrier on Basement Walls

Post by GeorgeKez » Tue Jan 22, 2019 1:24 pm

ok, thanks, I believe R20 is required code wise. Here is a link to the specs for durafoam. The folks at Home Depot said it would be considered a vapour barrier if properly taped and sealed but I will try to further validate that. George

https://www.plastifab.com/products/insu ... ofoam.html

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Re: Vapor Barrier on Basement Walls

Post by GeorgeKez » Tue Jan 22, 2019 3:32 pm

Hi Shannon, I found the specs for recommendations on a vapour barrier. Admittedly this is hard for me to decipher. It looks like it says that you can get away with a vapour barrier if Durafoam is the sole insulation material used top to bottom of the wall. But if you use batts in the frame then you need the 6 mil barrier. But... maybe not if the temperature meets a certain criteria according to their data charts. That's mumbo jumbo to my simple brain right now.I'll stare at it for a while longer. Hopefully this makes more sense to you to help answer my question on whether you can double up this stuff. Thanks again, George

Ontario code looks to go from R12 to R20 back in 2012.

https://www.plastifab.com/pdf/technical ... ations.pdf

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Re: Vapor Barrier on Basement Walls

Post by Shannon » Tue Jan 22, 2019 3:34 pm

Yes you need to verify that but you also need to be sure your local government inspection office approves of it.

Actually right in their own literature They say that anything less then 5" can not serve as vapour barrier. I kinda feel like I would be leary of that plastic/foil all doubled up in the wall? Sorry but my experience is with XPS products and I know how they work.
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Re: Vapor Barrier on Basement Walls

Post by GeorgeKez » Tue Jan 22, 2019 4:37 pm

Don't know how I missed the 5 inch requirement. That certainly answers the 6ml poly barrier question! But seeing I own this stuff I am thinking that doubling up to 2 inches is a safer bet than just going with the one inch. That would give me a thermal break of R7.5 and less chance of condensation forming from the cold side.

Again, thank you for your time. Regards, George

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Re: Vapor Barrier on Basement Walls

Post by Shannon » Tue Jan 22, 2019 7:23 pm

Good luck with your project.
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