vapor barrier in basement walls?

[dale rex]

I am finishing my first basement(I am just starting out in the remodeling business). I will be building 2 x 4 walls up against the concrete foundation walls, insulating them, and sheetrocking them to finish them off. My question is....where does the vapor barrier go in this situation? Does it get installed the usual way facing the interior of the building? If moisture would happen to enter through the concrete, wont it get trapped if the vapor barrier is installed this way? does it pay to use pressure treated lumber for this?

[Martin Holladay]

Re: vapor barrier in basement walls?

Dale Rex,
Use rigid foam (expanded polystyrene or extruded polystyrene) against the concrete. Do not install any plastic sheeting -- no poly -- anywhere. Do not install any fiberglass insulation. For more information, visit www.buildingscience.com.

[Mlandry]

Re: vapor barrier in basement walls?

Make sure to use pressure treated plates on the concrete floor.

[RJ Davisson]

Re: vapor barrier in basement walls?

Both of these are good advice. Not only don't you need a vapor barrier you're one step better toward eliminating potential mold problems. I'm not sure if the article covers it but something I've done on jobs is use the XPS, use P.T. 1x4 as strapping (with Ramsets through the strapping and through the XPS in the walls). If you can find a source use DensArmor Plus or DensArmor or equivalent instead of sheetrock or blueboard...a few extra bucks per sheet...this also eliminates potential food sources for mold to breed on. A few squirts of canned foam insulation and you're virtually airtight, depending on how you finish off around windows and along the sill/joints. You might have to rip the PT sills for the floor to accommodate the difference between 3-1/2 inches and the thickness of the XPS and whatever you use for strapping.

[Brad S]

Re: vapor barrier in basement walls?

Martin
Where in the buildingscience.com site does it give information on this?

[Martin Holladay]

Re: vapor barrier in basement walls?

Brad S,
Try this document:

http://www.buildingscience.com/resou...r_Renovate.pdf

See especially pages 16-20, 25, 28-30.

[Brad S]

Re: vapor barrier in basement walls?

Thanks for the info, Martin. Pg 36 states the worst thing to do is use batt insulation and cover with poly. I don't fit up too many basements and when I do it is in conjunction with new construction where I know the basement will be dry and I've been using pt studs and either no insulation or kraft faced, never poly. I haven't had any problems this way, but I guess that is because the kraft paper allows some drying to the inside. Building scienc.com doesn't seem to say anything particularly about not using kraft in a basement but for my climate (CT) kraft is recommended for above grade perimeter walls, not poly, I assume that applies to the basement as well. Anytime anyone has asked me to fit up an obviously wet basement I walk away from it.

[phillip]

Re: vapor barrier in basement walls?

I like to use metal track on basement floors


I wonder what FHA has to say about no plastic when you build thier walls in basements, common practice around here is plastic over the insulated 2x4s

[Hausdok]

Re: vapor barrier in basement walls?

Hi,

Check out Dow's Wallmate for the basement walls.

ONE TEAM - ONE FIGHT!!!

Mike

[stevenboston]

Re: vapor barrier in basement walls?

Late to this one but what have you found most effective dealing with inspectors who insist on poly and R13 ...2 inches of XPS is insufficient according to him. I'm thinking that with Certainteed's DryRight membrain faced fiberglass I could satisfy the code and not compromise the basement wall assembly. Seem reasonable?

[WilliamBonetto]

Re: vapor barrier in basement walls?

Regarding using pressure treated on the concrete floor of a basement. I have heard from a couple of guys that any treated lumber inside a house is illeagal. But on the other hand that has always been standard practice with the company that I work for. We are actually finishing a basement now and are using treated plates for the bottom. Just looking to actually clear this up once and for all.

[Brad S]

Re: vapor barrier in basement walls?

Steven
You could try using spray closed cell foam like Corbond to get the R-value you need. A little more expensive but no poly.

[kurtmit]

Re: vapor barrier in basement walls?

A quick plug for 2" of rigid foam direct to the foundation......

I did my 90 year old bsmt. w/the system described @ Building Science about 5 years ago. I was initially uncertain, but trusted in Joe L., and I want to testify that it is the nicest, cleanest, most excellent method of finishing a bsmt. wall I've ever experienced.

And, it was approx. $2500 cheaper for the material; I bought the foam @ Le Depot de Maison in the off season when they had it marked down to $15 a sheet for 2".

Logistics of installation were also amazingly easy compared to stick framing in a bsmt.; hauling the stuff in was easy, cleanup & waste removal was a snap, installation went flawlessly, etc.

Can't say enough good stuff about it.

[gregoryj]

Re: vapor barrier in basement walls?

Kurtmit,

What technique did you use for covering the foam with drywall?

[kurtmit]

Re: vapor barrier in basement walls?

The foam is secured w/furring set into horizontal rabbets (in the foam); tapcons through the furring into the foundation.

Drywall glued & screwed to the furring & foam.

On one wall section, I didn't even use furring. I glued the foam to the wall, glued the drywall to the foam, and secured the assembly in place w/baseboard, a 1x6 ceiling molding, and an apron/stool shelf midway up the wall, fastened w/tapcons. It worked great. Better than I could imagine. Nothing's moved even a millimeter in 5 years; it's solid as a rock.

Honest, if I was doing it again, I might do the whole bsmt. without any furring, and rely on the the glue/baseboard/shelf/ceiling molding approach.

I have had more excellent carpenters tell me this system can't work, variations in the foundation will make getting the wall flat impossible, fastening is problematic, glue won't hold, etc., etc. They are all wrong. The foam tends to "float" over uneven areas of the wall, and provided an amazingly flat substrate for applying drywall.

I would almost guarantee that if you finished a bsmt. this way, you'd never go back to stick framing. Ever.