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rimist · Jan 26, 2011, 01:33 AM

I am on the West coast of Central Florida. I have 2x6 rafters, and have purchased kraft faced r19 batts of insulation, however, after some research I would like to install a radiant barrier as well. My attic gets hot... I've broken thermometers trying to figure out how hot, easily 130. Even this time of year my attic is easily 15 degrees hotter than the outside. I do have both soffits and ridge vents, both of which are not obstructed. I planned on purchasing foam rafter vents to ensure that the air could continue to circulate. Humidity outside the home is typically high, 90% isn't unusual. Any advice or instructions would be appreciated. I cannot afford spray foam insulation, so please don't go down that road.
Thanks

joypulv · Jan 26, 2011, 04:28 AM

You have a bare attic under a pitched roof? (To me a cathedral ceiling is finished living space using the rafters.)
Have you read the Florida Solar Energy Center info on feasibility (type of roof shingle/tile, air handlers, etc) and also questioned whether to insulate the attic floor instead of the 2 x 6 rafters. I see that many homes in FL have attic exhausts set to come on at a certain temp.
Humidity is a major concern too, and it seems to me that having as much air in the rafters as possible is important.
Fi-Foil has training presentations on their site for installing.

joypulv · Jan 26, 2011, 04:29 AM

Also you wouldn't put RBS over faced insulation.

rimist · Jan 26, 2011, 07:51 AM

Yes, I currently have a bare attic under a pitched roof, which is what I am referring to installing a radiant barrier and insulation on. I also have a cathedral ceiling in part of my house, but I can stand on the top of it and barely touch my roof.

rimist · Jan 26, 2011, 07:55 AM

I agree... I was thinking of putting the rbs in the middle of the 2x6, and attaching the faced insulation with the face "up" to the edge of the rafters. This would provide air on both side of the rbs, but I'm hesitant about the effect of having a

rimist · Jan 26, 2011, 07:58 AM

Vapor barrier 5 1/2" from my decking. Part of the purpose of the additional insulation is to simply drop the temp as much as possible, because I would like to use the attic space for storage, which would reduce another cost for me.

joypulv · Jan 27, 2011, 06:50 AM

It's easiest to just use Answer, even for your own post.
What color is your roof? That's a big factor.
Ridge vents are low profile with just a few thin air slots either side, is that what is too small? How do you know it is barely working? (Maybe this is why so many people have electric vents in the south.)
I have no clue about the feasibility of putting the RB in between the rafters, over vent channels and under fiberglas. A lot more work, but if your labor is free... Maybe ask the FSEC about moisture problems with that arrangement. Or consider 1" foiled isocyanurate (foam 4 x 8), over the rafters and unfaced fiberglas. It has an R of 6 per inch.
If your roof is gabled, consider a small attic ceiling with venting above it in each gable?

rimist · Jan 28, 2011, 03:22 PM

The ridge vent is eight to ten feet long, while the soffits are each twenty five feet long. When I pushed up gently on the vent, I could feel air movement, which was almost nonexistent before I pushed on it. This afternoon it was 66 outside, 74 inside and 87 in the attic. The roof color is GAF weathered gray, mandated by my hoa

joypulv · Jan 29, 2011, 12:43 AM

You have a hipped roof?

rimist · Jan 30, 2011, 01:18 AM

I have a gable roof

joypulv · Jan 30, 2011, 05:15 AM

So how about a new full length ridge vent (not expensive) and a small ceiling with vents above it, in each gable? And iso or RB over unfaced batts over vent channels?