open cell or closed cell in attic??

JulesB · 02-12-2011, 05:30 PM

I figure there's been a discussion or two on this already, so I apologize if it's redundant.

I'm doing a complete rehad on an older home. I fully intend to spray foam insulate it, including a conditioned attic. (my attic is very small, due to a lot of vaulting, and I'm settting an air handler up there) I went to the annual remodelers home show here locally today, in part, to look for, a foam contractor. There were 5 to choose from, and I discussed pricing, etc, etc. with each. My question is this. Three of the companies said to use closed cell on the under side of the roof, and the other two said to use open cell. Both had good arguments for their choices. Curious to hear what you all think.......

Thanks,
Jules

hayewe farm · 02-12-2011, 09:41 PM

Any leak will flow through open cell foam but will not through closed cell faom.

JulesB · 02-13-2011, 08:34 AM

Quote:

Originally Posted by hayewe farm

Any leak will flow through open cell foam but will not through closed cell faom.

I'm not sure which would be worse. A leak coming down to your finished ceiling that will be made noticible, or an unknown leak that's trapped in the roofline, creating mold and rot.

iamrfixit · 02-13-2011, 09:51 AM

Well it is easier to fix if you know about it, even if it ruins a piece of drywall or two. I really wouldn't want the first sign of a leak to be the roof sagging because the rafters were completely rotted.

That is no different than all of the houses with regular insulation and roofs, the roof leaks, water comes in, leak and damage gets fixed.

Personally I would never spray foam the under side of any roof period, with any kind of foam. The top side of a ceiling would be fine but I would keep an eye out for any roof damage, inspect things in the attic occasionally and replace the roof before it got to the point I had to worry about it. If I did it then; I would use closed cell.

Open cell expands a huge amount and creates heat. As the foam cools back down it shrinks slightly and tends to pull away from the cavity leaving slight gaps that lowers the efficiency. I have seen this first hand, while the gap is slight it is still a place for air to get through.

JulesB · 02-13-2011, 10:09 AM

Quote:

Originally Posted by iamrfixit

Personally I would never spray foam the under side of any roof period, with any kind of foam. ....... I would use closed cell.

I'm a little nervous about it myself. Though, I think I'm going to do it. My attic area is very small, most of it being eaten up by vaulting. What little area there is, is going to have an air handler in it. That's the motivation, to make the a/c more efficient.

Open cell expands a huge amount and creates heat. As the foam cools back down it shrinks slightly and tends to pull away from the cavity leaving slight gaps that lowers the efficiency. I have seen this first hand, while the gap is slight it is still a place for air to get through.

Ironically, that was the argument coming from the open cell guys. They claimed that due to the rigidness of closed cell, repeated expansion and contraction of the roof would create small air gaps.
I tend to disagree, especially if they "wrap" the rafters.