frost on new walls…wait to insulate?
Hard to think up a title for this, but…
Being anal about insulating new walls, DW and I are trying to “properly” install FG batts in 2X6 walls. We are placing 1/2″ foil faced urethane foam (“THERMAX” i think)with taped seams between the FG/studs before sheetrocking…the foil face acting as extra insulation, thermal barrier, and vapor barrier. That’s goin OK, but last night, while placing batts, we noticed a bit of frost on the lower 1/4 of the inside of the OSB sheathing. Temperature outside -3 F, structure is being temporarily and sporadically heated to ~ 40 F inside, with a forced air furnace whenever we work on it, like weekends and evenings. We always shut the furnace off when we leave. This has been going on for a couple of months as I finished electrical and plumbing rough-in, and now drywall. Will get the lid on and 16″ of cellulose blown in the attic this weekend, (I found a Nu-Wool contractor who will blow in R44 @ .70 a sq ft) then I can leave the heat on all the time.
Question is, should I wait till I can get it consistently warm enough in there to prevent the frost BEFORE I place anymore batts and foil faced? If I cover over the frost, where will this moisture go once I have the wall buttoned up? I should mention that this is 1/2″ OSB sheathing with Typar on the outside.
Or am I being too anal?
Edited 1/28/2004 9:31:53 AM ET by johnnyd
Replies
IMO, it's not enough moisture to be concerned about. It will find its way out. The sheathing and tyvek are plenty permeable.
My theory is that at my pace (evenings and weekends), the FG with foil faced over it will sit long enough un-taped and with a gap at the bottom (which I will foam before flooring), before sheetrock, that it will mgrate out through the gaps before it's really buttoned up.
If you are cutting this thermax to fit between studs instead of installing over then, you are not getting much of a vapour bar anyway. Everyedge is a penetration point for moisture to be driven into the wall. You may want to run plastic over the studs and tape it before sheetrocking.
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Thanks Piffen. The Thermax is going OVER the studs, plates, everything...before the sheetrock. So you don't think it will hurt to FG over a little frost?
No. That small amt will dry to the outside over the next couple of months before it causes problems.
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