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Old 04-13-2009, 08:49 PM   #1
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Finishing Attic - Framing (Raftters) & Insulation

I am in the process of finishing an attic wanted to get your suggestions on insulation options and avg costs (lower the better :-).

Currently the rafters are 2x6 16" OC and need R-30 insulation by code. I have had some contractors quote the job but would rather DIY the project. They have suggested all types of solutions from radiant barriers, foam, and batt solutions.

Note: The builder of the house installed foam baffles between the rafters.

If I go traditional batt I would need to fur down the rafters another 4 inches (which opens a new question) to get 10" for insulation, some contractors said they could use a 2x2 with batts, but I am not for sure how they would do that without compressing the insulation.

If I was to fur down using 2x4x8s (46 total) what would be the best method to attach these to the rafter to meet code (brackets, glue and toe nails)?

I found this photo, would this method work for furring them down?

The other option would be to use DIY Spray foam or spray foam batt hybrid. This option hopefully would be offset some by not having to purchase all the 2x4's. Has anyone had any success with the DIY Foam and or recommendations about it?

The radiant barrier (Prodex?) which they claim two layers equal R - 21.10, does this stuff meet code, and since it does not reach R30 I assume I would have to use bat with it also?

The last option, could I use a combination of two or all three to get to R30 with minimal costs? Possible 1" Spray Foam to seal it in between the rafters and radiant and/or batts to get it R30 with out furring it down?


Last edited by andgrim; 04-13-2009 at 08:54 PM.
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Old 04-13-2009, 10:53 PM   #2
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Acouple years ago I built an addition and used a process I learned in the early 90's.

In The Colton Addition ,
  • I first started with rafter vents,
  • then placed R-19 Kraft Face insulation,
  • then I screwed on 2" Foil Faced insulation using 3" drywall screws with the 1-1/4' perferrated washers (sorry the correct term escapes me...Dave/Gbar can you help?)
  • then I strapped the ceiling using 5" star tip screws from GRK
  • This whole process gives you exactly R30.
You have to build down your rafters buy ripping down 2x6's to 2" strips and install them "full lenght" using GRK 4"star tip screws.

Hope this helps and this process will meet code.

Good Luck


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Old 05-01-2009, 08:40 AM   #3
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8 1/4 inch R-30

Dealing with same - Found on owens corning website R-30c which is 8 1/4 inches deep. Made for catheral ceilings. Hope this helps.
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Old 05-01-2009, 09:33 AM   #4
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Another option would be to use R19 fiberglass in the 2x6 space and cover that with 2" Celotex foam boards. Screw in 1x3 furring stips over the celotex with 3 1/2" screws.
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