# Insulating an existing cement basement wall



## reg russell (Sep 17, 2011)

My basement partial wall has a vapour barrier over the cement then 2x4 and panelling.
I would like to install foam board insulation but wondered if the foam board should go over the vapour barrier or cut it out and put a new barrier over the foam then the drywall material?


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## CyFree (Jul 22, 2008)

If you are using foam board insulation, according to the US Department of Energy, you don't need any vapor barrier, provided that you place it straight against the walls and seal the seams between boards with mastic tape. 

Foam board insulation itself is impervious to water and acts as a vapor barrier. 

Also, according to the US DOE, you do not need a frame to install the drywall. Furry strips can be installed over the foam boards to hang drywall. 

http://www.eere.energy.gov/buildings/building_america/pdfs/db/35017.pdf


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## AGWhitehouse (Jul 1, 2011)

CyFree said:


> If you are using foam board insulation, according to the US Department of Energy, you don't need any vapor barrier, provided that you place it straight against the walls and seal the seams between boards with mastic tape.
> 
> Foam board insulation itself is impervious to water and acts as a vapor barrier.
> 
> ...


I concur...


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## Tiny207 (Mar 12, 2011)

CyFree, I'm in the planning phase of finishing a room in my basement... Do i need to put the Foam board/ridgid Insulation directly to the concrete foundation or can i put up the 2x4 wall an then place the insulation in between the studs? I am trying to save space in this room and do not want to use 2x2s. The room is dry no issues with water except for condesation from the water main in the room.

Thanks for Help!



CyFree said:


> If you are using foam board insulation, according to the US Department of Energy, you don't need any vapor barrier, provided that you place it straight against the walls and seal the seams between boards with mastic tape.
> 
> Foam board insulation itself is impervious to water and acts as a vapor barrier.
> 
> ...


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## AGWhitehouse (Jul 1, 2011)

Tiny207 said:


> CyFree, I'm in the planning phase of finishing a room in my basement... Do i need to put the Foam board/ridgid Insulation directly to the concrete foundation or can i put up the 2x4 wall an then place the insulation in between the studs? I am trying to save space in this room and do not want to use 2x2s. The room is dry no issues with water except for condesation from the water main in the room.
> 
> Thanks for Help!


Look up z-furring...it's what you're looking for.


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## Tiny207 (Mar 12, 2011)

AGWhitehouse said:


> Look up z-furring...it's what you're looking for.


I need to insulate the 2x4 wall against the concrete wall but cant give up any more the 4" (2x4 + drywall). The doorway to the room is next to the concrete wall and can't have the 2x4 wall on top of the ridgid insulation.

Or can I place the wall against the concrete and just use regular batt insulation?


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## AGWhitehouse (Jul 1, 2011)

Tiny207 said:


> I need to insulate the 2x4 wall against the concrete wall but cant give up any more the 4" (2x4 + drywall). The doorway to the room is next to the concrete wall and can't have the 2x4 wall on top of the ridgid insulation.
> 
> Or can I place the wall against the concrete and just use regular batt insulation?


http://www.vobb.com/Other-products/Z-furring.jpg

assembly is 2-1/2" (2" foam & Z, 1/2" drywall)


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## Tiny207 (Mar 12, 2011)

AGWhitehouse said:


> http://www.vobb.com/Other-products/Z-furring.jpg
> 
> assembly is 2-1/2" (2" foam & Z, 1/2" drywall)


Sorry should be more in depth with my plans...

I am planning on mounting a 46" TV that weighs approx 50lbs... this wall will also have the recessed Electric/Cable/phone/home theater outlet for the TV running through it which is about 2 1/2" deep.

So it appears this Z furring will not hold this, along with any shelves i'd like to put up as well.

Thank You.


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## msaeger (Mar 1, 2011)

Could you use screws long enough to go through the insulation and into the community concrete?


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## AGWhitehouse (Jul 1, 2011)

Tiny207 said:


> Sorry should be more in depth with my plans...
> 
> I am planning on mounting a 46" TV that weighs approx 50lbs... this wall will also have the recessed Electric/Cable/phone/home theater outlet for the TV running through it which is about 2 1/2" deep.
> 
> ...


You'll need 2x3 framing minimum for that 2-1/2" box. I can't recommend putting the foam within the stud bays.

You could use the z-framing and surface mount a 1-1/2" deep 4x4 box on the concrete and spray foam around it to fill flush the insulation. Then use a 1/2" stucco ring to bring the face of the box flush with the gypsum board. You'll have to provide a piece of 1/2" conduit down to the box within a routed out channel in the rigid foam. You can spray foam fill after the conduit installation.


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## Gary in WA (Mar 11, 2009)

Do more research on the Z-furring. Buy the G90 coating not the lesser thickness ones (G-40,60) due the wet nature of the foam board most of the year. The stored moisture would rust out the metal at the fasteners. I would use stronger studs than 2x3's for shelving........ not to mention a heavy tv.

Gary


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## AGWhitehouse (Jul 1, 2011)

(1) 2x3 could certainly hold a 50lb. TV...Add two together with a plywood backer (the typical rough install for known bracketing) and you have an assembly that could easily hold you in the air...


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## Gary in WA (Mar 11, 2009)

Thanks for rest of the install information!

Gary


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## AGWhitehouse (Jul 1, 2011)

GBR in WA said:


> Thanks for rest of the install information!
> 
> Gary


"feel free to PM me rather than taking up valuable time/space from us both"

OP, if you're looking to have bookshelves and TV's hanging from the walls, then a typical stud frame wall is your best bet. If you really want the Z-furring option, then look into floor standing bookshelves. I believe a 2x3 stud partition will hold your tv just fine, but if your looking to have a library of books around it on wall mounted shelves, then look into larger studs.


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## ~Coach Dave~ (Sep 7, 2011)

Interesting post - I have a walk out basement (fully exposed walls) and am going to reside with tyvek, foam board, siding. I read over the DOE-generated doc at the link above and it appears that insulation differs between in-ground basements and half/fully exposed basement walls. I don't know what insulation is behind the drywall, but I plan to reside and if it's still super cold in my basement (God I hope it isn't) I'm going to pull the drywall down and put up foam board. Unfortunately my basement is finished and it's much more work trying to retrofit insulation...


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