Hello,
I’ve read most of the open / closed cell foam discussion here and on the JLC building science forum and haven’t been able to find an opinion on an issue I have coming up.
I have built a 24′ x 36′ addition (cathedral ceiling) that will be all but impossible to vent traditionally with baffles over fiberglass. The roof is framed with a LVL ridge beam and valley beams extending from the midpoint on one side to the far corners on the other side. and 12″ I-joists. I am planning to insulate the roof with Icynene – in fact they are scheduled to come out this Thursday. My insulation contractor recommends 6″ of Icynene. However,I need R-30 or greater so my options are thicker Icynene or R-19 fiberglass batts in the remaining 6″. Has anyone had any problems using Icynene or any other open cell foam with fiberglass in the same cavity? I don’t think I’m going to gain much from spending the addition $$$ for thicker Icynene – other than making my inspector happy with the R value.
Project is near Washington DC, so mixed heating / cooling. Planning to avoid a poly vapor barrier and used well caulked drywall and paint.
Thanks,
Art
EDIT – sorry – didn’t see the post earlier this morning asking nearly the same question 🙂
Edited 12/18/2007 12:19 pm ET by Arth
Replies
Had a nice chat with an Engineer with Icynene this afternoon. For anyone else who's interested, here's his advice:
Fiberglass under the foam is fine although unnecessary. If a vapor barrier is used, it should be between the foam and the fiberglass - ideally VB paint directly on the foam.
I'll include it to make the inspector happy. $400 for fiberglass vs. >$1000 for additional Icynene.
I'd probably go for no VB in this case myself.But what has me curious - isn't the Icy rated R5 per inch? Six inches gives you R-30 then, right? What am I missing?
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
3.6 per inch for a total of about R20 with 6 inches. My inspector wants the min of R30. I could try to convince them that R20 with foam is acceptable according to an alternate method - and Icynene would help with that - or pony up extra $$$ for R30 Icynene or pay a couple hundred to have them put R19 batts in under the foam.
No chance you can get the polyurethene foam instead?It rates at R7 and is a VB itself.Can you really place FG battts cheaper than to just have them spray another couple inches of Icy? I don't know how they can sell the stuff if you still have to come in and re-insulate with a different product!
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
If it was my addition I'd spend the extra $600 or more to get the best R value possible.
Fuel prices are only goin' up.
If you get cold enough weather to move the dew point inside the foam and into the FG you end up with a real mess.
If money is the dealbreaker... Dense Pack Cellulose is (in my area) running about $2.75 - 3.75 pr foot at 11 1/2". Based on the pitch and the prep work needed. (r 38 +)
Good luck
Garett
Well, seems I'm a bit dense and wasn't reading the printed quote correctly. It's really not that much more to spray more foam. I did also look for closed cell but that doesn't seem to be as common around here. All the companies I contacted sprayed open cell. My inspector did tell me that he's seen one closed cell job but I didn't think to ask him who did it at the time he mentioned it.ThanksArt