Attic Rafter Insulation. What Should I Do? - Insulation - DIY Chatroom Home Improvement Forum

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Old 04-21-2013, 09:39 PM   #1
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Attic rafter insulation. What should I do?


My wife and I are in the process of buying a century old money pit. It needs tons of work. We fell in love with this house. There is no one currently living there, so the real estate agent allowed me to use my fold up ladder to get inside the attic. I was both scared and happy. On the plus side, the attic can eventually be converted into a play room for the kids, or something. The floor of the attic is covered in planks, and there is loose insulation between the planks and the ceiling of the floor below.(some planks are missing, so I could see, I think there is 4-6 inches of the stuff)

I believe the roof pitch is 8/12. in the middle of the attic for the length of the house there is at least 10 to 12 feet of head space, that goes down to the floor of the attic.

Someone at some point attempted to add fiberglass insulation to a couple of the rafters, but did a lousy job. There are no baffles, and the fiberglass is in some areas loose with no plastic. In other places the fiberglass is just falling out. some parts look as though they jam-packed fiberglass where the soffit would be.

The roof is an old metal shingle roof, and still in fairly good shape. there are only two vents, one on each side.

I need to insulate this. what would be my best bet keeping in mind that I want to set it up so that I can eventually build a room up there?

I believe the space between the rafters is 18 inches, with the rafters themselves being 2x6.

My thoughts were to remove all of the crappy stuff that's falling apart anyways, clear the soffits, add baffles from top to bottom between the rafters, add R22 fiberglass on top of the baffles, plastic sheathing over that, then drywall...

Am I thinking along the right lines? should a ridge vent be added? Any help would be greatly appreciated!



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Old 04-21-2013, 10:10 PM   #2
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#1 Please go back and add your location to your profile, imposable to make many suggestions without it.
Just go to Quick links to edit.

It's a common newbee misconseption tha t when you see all that "wasted" space that you can just add a room up there.

I think your going to find your joist are under sized for a real floor, there will need to be a permit for this type of work, there needs to be a real set of stairs built to get up there to make it legal


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Old 04-25-2013, 06:53 AM   #3
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R49 in Ceiling? You should know that most jurisdictions have adopted the IECC 2012 code that requires ceilings to have insulation with an R value of 49. That's huge! Even if you use 12" rafters, you won't be able to get more than an R-38 using Owens Corning batt insulation, and would need an additional 3 1/2" (R11), plus the extra 1" air space above the rafters for ventilation. If you don't have 16+ inches, (and who does?), here's an alternative. Do an unvented ceiling with a vapor barrier placed above 3" of closed cell foam (R6 per inch) and then 8" of batt (R30) below that. The closed cell insulation also acts as an air barrier.

Last edited by Beyhan Trock; 04-25-2013 at 06:56 AM.
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Old 04-25-2013, 10:46 AM   #4
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The above response is correct in that those ceiling joists may not support the live/dead loads of an occupiable space. Also, those 2x6 rafters don't have enough depth to properly insulate nor enough strength to accomodate exterior-applied ventilated nailbase panels. The only way you're going to get a room in that attic is to rip off your roof, lay in a new floor, and build a properly insulated/ventilated roof deck. That gets pricey, so if that's not an option, call in the cellulose crew and blow in an R-49 thickness and plan on a play room elsewhere...
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Old 04-28-2013, 09:56 PM   #5
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You will need more than 3" of SPF to get the R-30 required (plus cavity insulation) to control condensation for a closed roof system for your location- Our Zone 7, see map;

Be sure to check weight limits/span on existing ceiling joists with added cellulose (R-49= 1-1/2# per sq. ft.) loaded on already 8# per sq.ft. for plaster/lath, or if 1/2" drywall, 24"o.c.;

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attic , insulation , rafters

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