Scissor Trusses, Foam And FG - Insulation - DIY Chatroom Home Improvement Forum

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Old 11-13-2012, 06:07 PM   #1
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Scissor trusses, Foam and FG

Hi all, I'm looking to make a decision on some insulation so I can get on to the "funner" stuff in my house project. I'm in southern MO, on the 3-4 border.

I have a cathedral ceiling over the living area with an open "loft" on one side (above the 2 bedrooms). The ceiling over the LR is scissor trusses with (24" centers) 2x4's under the roof deck and 2x6 ceiling joists. The Loft ceiling has a 2x6 under the roof deck and the rest is 2x4.

Loft side Ceiling and knee wall

LR/Cathedral ceiling side

The foam contractor insists that 2" of CC under the roof deck is all that's needed, everything else is throwing $ away. Another source strongly opposes this opinion. So, assuming I go with 2" of cc foam (or there a bouts) under the roof deck, is there a good way to add actual R-value with fiberglass? Netting or lacing batts or rolls under the foam (direct contact with foam) is starting to look like a labor intensive way to go. Putting batt/rolled FG on top of the drywall is by far the simplest, but I understand this may not be wise because is will create an open gap below the foam and above the FG.

So any thoughts? Is adding FG above the drywall indeed a bad idea? If so, is there an easier method than netting to put the FG in contact with the foam? Or would you think that popping for an extra couple of inches of foam ($$) would be the way to go?

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Old 11-14-2012, 10:38 PM   #2
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Two inches is about R12, max. Is that code for your area? I doubt it. I'd go thicker, or look at a different insulation scheme that gives the proper R. I have heard that some sprayers say 2" is enough because the appropriate thickness is so expensive it scares people away. Cobbing in batts would be a PITA. Why not air seal and then just blow in cellulose and be done w/ it? For the cathedral part, see and search for "how to insulate a cathedral ceiling". They and/or have maps of recommended R value, geographically.
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Old 11-15-2012, 06:15 AM   #3
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You have to have some insulation beyond just the 2" of CC SPF up there. At 2", you have somewhat supplied the vapor and air barrier but you gotta get more R-Value in that assembly as well.

Roxul or HD FG batts will work as well. You could also net and blow insulation too.

Post up some pictures.
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