Finishing Basement: Fastening Exterior Walls to Floor

[bambam]

Kevin,

I'd be very cautious about plastic sheeting on both sides of the wood. Code here (Calgary, Canada) used to require a moisture barrier between the studs and concrete wall from floor to joists, in addition to the required vapour barrier. That proved to be a moisture envelope -- so code was changed to require a moisture barrier four feet from the floor or to ground level.

In practice, as long as a basement does NOT have a plastic moisture barrier from floor to joists, the city inspectors are happy. If there is a full height moisture barrier, they will ask you to cut large X's in it .. to open it up.

Why not phone your municipality and ask what code requires .. and what their experience is.

Ken

[Goedjn]

I think the air-gap is a bad idea. If the pocket is sealed off, then at best it does no good at all. If the pocket is vented to the inside, then you've created an inaccessible area where mildew and vermin can hide, from which they can invade your living space. If they're vented to the outside, then you're guaranteeing moisture in the pocket, where it might not otherwise be. This might be a good idea if you KNOW you've got water problems that you can't actually solve, but:

Far better to solve any bulk-water intrusion issues first, then seal the wall against vapor, and put close-cell foam (either spray or panel) up against the wall. and then build the studwall against that. The indoor side of the foam won't condense moisture, because it's not cold. The wall-side of the foam won't condense moisture, because water vapor cant get there, and there's no room anyway. No moisture, no mold.

[kevharper]

Thanks for the info.

Code here only requires the barrier on the warm side of the wall but I thought doing both sides might be a belt & suspenders solution for a small increase in cost. I think I'll just do the one (warm) side and leave it at that. It's a lot easier that way.

It turns out my concrete walls are not plumb vertical so I have a V-gap going from the base of the wall to the top with the gap at the top being about 2 inches. I'm stuck with that unless I really stuff it with insulation which I don't plan on doing. So there will be a small air gap.

1 of the long exterior basement walls will be in an unfinished area and I won't be insulating it. I also won't be heating or cooling the basement (other than using the HVAC from the rest of the house) so I don't think I will have moisture problems either way. Plus I have had the aluminium foil test going on for several days now (including this severe rain) and there's no evidence of moisture on the walls or floor.

So I think I'm going to stick with the vapor barrier on only the warm side and allow the gap to be whatever it turns out to be. Keep my dehumidifier down there for insurance and just get down to business. I got to GET 'ER DONE!!

Thanks for all your feedback guys... Kevin