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-   -   Rafters insulation? (http://www.diychatroom.com/f103/rafters-insulation-159862/)

weberus3 10-12-2012 04:12 PM

Rafters insulation?
 
Ok I'm getting ready to insulate my rafters in a attic playroom I'm finishing. I got my hands on enough "free" 4x8x3/4" foam insulation board to insulate all of the area between the rafters. My question to everyone is this enough insulation or will I have to add Insulation Batts also. So I have about 6-8" of space in the rafter channels to the edge where the sheet rock will go. I have already installed rafter vent baffles and have roof ridge vents for venting. I live in the Memphis area so our winters get as low as teen's and summers get into the 100's.
**corrrection** I got to inspect the foam insulation this weekend and found it to be in different thicknesses 4x8 sheets still, but my choice of 4", 8", and 10" THICK! Again its going in between the rafters not the floor joist.****and its FREE.

funfool 10-12-2012 04:22 PM

not enough, but some is better then nothing. If it is free or cheap use it.
For best results blow it in, can rent a machine at Home depot and buy the bags of insulation.
Would not hurt to blow it over the foam later, but very little R-value in 3/4" foam, depending on the foam, is probably r-7 or less.
But still better then nothing.

joecaption 10-12-2012 04:31 PM

http://www.energystar.gov/index.cfm?...sulation_table
The baffles are going to take up about 1-1/2" of the avalible space.
I at least add 2 X 2's to the rafters so I can at least add R-13.

beenthere 10-12-2012 04:36 PM

Moved to Insulation forum.

Gary in WA 10-12-2012 11:47 PM

Appears you are in Zone 4, requiring R-38 in ceilings; http://publicecodes.cyberregs.com/ic..._11_par002.htm

http://publicecodes.cyberregs.com/ic..._11_sec002.htm

Don't use cellulose in the cathedral areas. I would use Roxul, install full sheets on the rafters for one layer after filling cavities, if you have enough, then drywall. Or just some rips to cover the rafter edges to prevent thermal bridging, foam air-seal one layer of the cavity foam. ADA the drywall; http://www.buildingscience.com/docum...wall-approach/

Gary


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