-----Original Message-----
From: B-P Golden Oldies: "The Cracked Monitor" [mailto:[log in to unmask]]On Behalf Of [log in to unmask]
Sent: Wednesday, April 26, 2006 5:48 AM
To: [log in to unmask]
Subject: Re: [BP] Polyurethane foam insulation



In a message dated 4/25/2006 10:25:03 A.M. Eastern Standard Time, [log in to unmask] writes:

I agree--closed cell won't breathe so it serves as a moisture barrier.  Make sure you know where your dew point will be (where in the wall condensation will occur) to avoid letting moisture come in contact with wood or concrete

In my former capacity, we always insisted that backer rod for caulking be closed-cell polyurethane foam, because outgassing from the open-cell stuff had been found to percolate out through the sealant and ruin it.  Why isn't there going to be some deleterious effect (on paint?) of open-cell polyurethane insulation?
 
Seems to me there's an inconsistency between Bruce wanting open-cell polyurethane insulation and me wanting closed-cell backer rod.  Or am I missing something?
 
Ralph

Bruce Marcham replies>
 

Ralph:
 
I'm not saying I'm in favor of open-cell foam, just agreeing that closed cell foam serves as a vapor barrier and saying that it needs to be taken into account. I think that if you do you use it as a vapor barrier you can get around some of the problems of where the moisture is going to condense (as in not in the middle of your fiberglass insulation). In some instances that feature can be used as a strength, not as a detriment. The wrong thing to do is to put a 4'x8'x1/2" sheets of it on the outside (up here in the north) under your vinyl siding (which porbably breathes okay) and not realize that in doing so it means that the condensation will then take place in the fiberglass in your 2x4 walls.
 
I should also say that I am not an expert in this area, just that I have given it some thought and found myself confounded by the issue at times (most of the time). 
 
I have an associate, a fine cabinetmaker who also does high dollar home additions and improvements, who swears against using modern building materials such as house wrap, foam insulation, etc. in favor of tar paper (or maybe just kraft paper) and fiberglass because he feels you'll never win in the moisture migration problem so he'd rather just let the house breathe. I'm not in favor of throwing our hands up and taking that approach but would rather try to work with the modern materials to achieve a tight house and then do energy recovery in a ventilation unit designed to get a healthy amount of fresh air into the house.
 

I hadn't considered the issue of the off-gassing. I would would imagine that the closed cell foam does that to some degree as well but maybe much slower (after an initial high rate as the surface releases the gas)?
 
 
Bruce
 


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