I need this vapor barrier issue spelled out!
I am finishing my basemnt in PA. Poured concrete wall has been DryLocked with two coats, even though basment walls are dry and no other water issues in basement.
Metal studs installed two inches from concrete wall and about to begin insulatiing with kraft faced R13.
Do I need to put poly up as well? I am happy to do the extra step but it seems, in this neighborhood, none of the basements contractors have put up poly and sttled for kraft faced.
This project has gone very well so far, and I don't want to blow this crucial step.
Thanks

 

You will get a huge variety of answers on this subject. Some will tell you to place a vaor barrier against the block wall and against the drywall. While others will tell you you only need the barrier against the drywall.

I am one of those that believes that a vapor barier is simply a vapor trap. Your biggest source of water (assuming you don't have a flood) is going to be during the summer with high tempatures and humidity. At that point the air inside your basement will be cooler than that of the outside. Air moves hotter to colder so the vapor will be coming in from the outside trying to work in. If you place a vapor barrier the mosture will be trapped. This will lead to mold in the insulation since it can't dry.

I hope that muddies I mean clears the water for you.

 

Ill go 100% the other way. Have been doing basements for over 30 years now. Some full earth contact homes. Hang a 4 mil poly on the cement walls ,from the sill plate. 1" space to the wall . A , R -13 in the wall paper to the room. polyV /B on top of this then the dry wall. Dont cut it out over the electric boxs or the windows till done drywall and paint then cut them out. Helps keep them clean.

Have been back on many and no mole in the walls at all

ED

 

Have to agree with Ed.

Spent the last 2 weeks researching this, in fact Ed's way is the code here in Ontario. Heres, what I did.

Poly on the concrete block from ground level down to the floor and under the footer beam. Bead of sealant underneath. Thats the vapour barrier.

Put the insulation between (and behind if using steel) the studs then another sheet of poly over the wall, joined to the vapor barrier which is turned up from the footer. This is the air barrier.

In short, there are 2 barriers, one to stop moisture from outside and another to stop moisture from the living area. As long as you don't seal above ground level on the block , any moisture in there has a way out. There should be no gap between the insulation and the wall.

Hope this helps

 

Thanks for the info, gents.
Will proceed with the V/P route.
Bill

 

http://www.eere.energy.gov/consumeri...riefs/eb7.html

You ought to read this before proceeding. It is very informative.

 

Hey Bill,

I'm in PA too, doing pretty much the same thing you are. Not to throw you off track here, but if the contractors don't do it, why should you? Granted, builders aren't gods and always try to save a buck, but it doesn't cost much to slap some poly on the wall, so there has to be another reason.

Personally, I think plastic will make it so airtight that if a drop of water ever gets behind it somehow, it will never evaporate and you'll have a garden growing there. I'd go with paperfaced and give the whole thing a chance to breathe a little.

 

Markiz37 That builder will save more than a buck on the wall there, Add labor on it also.Thats like some of the post here way up in the north. Brown spots on out side walls from nails and rust. Paper back insulation but the moisture did get into the insulation. That why . Paper to the room and a poly over it all as one sheet.With poly on the cement wall also.

ED

 

If you were closer, I'd hire you just for your confidence But I'd get one hell of a warranty from you

A question for you then: I see the point of having poly under drywall to keep moisture out of insulation, but why in the world would you put another v/b over cement???

 

The cement can get damp from out side if the tar seal are what you have on the out side there leaks some . Or if it was to get wet from rain or snow the hydrostatic pressure in the cement would let the damp go down in it and to the insulation. like when you think you have a leak around the chimney sometimes it can be just that, that lets the water come on down and out of it.We still put a full drain around the out side and also on the inside of the footing under the slab and run it out open or to a dry well.

ED