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Old 11-04-2007, 06:39 AM   #1
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Insulating slanted ceilings (hot roof?)


Hi guys, here's my dilemma. I'm working on renovating the 2nd floor in my house and it has sloping ceilings in most of the rooms. There's currently NO insulation in the walls and ceilings, so I need to insulate. The walls are plaster and laths and the rafters are 2X4 16" on center. I was thinking of blowing in but I'm worried about water vapor building up and causing mold and what not. I'm kinda stuck as to what to do, I'm on a budget and need to do the work myself so spray foam is out of the question. Anyone have any ideas on what I can get away with here? Thanks in advance!

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Old 11-04-2007, 09:44 PM   #2
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Insulating slanted ceilings (hot roof?)


Are you sure about the roof rafter size? With the snow load in your state, 2x4's make no sense.
Are these exposed? You mention that the walls are plaster and lath, but leave out the ceiling construction.
What's the span of these 2x4's and what's the roof slope?
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Old 11-05-2007, 06:34 AM   #3
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Insulating slanted ceilings (hot roof?)


Yep I'm sure they are 2X4, they are exposed right now. This house was built in 1887. The roof was hacked up on one side to put on a dormer addition at some point, but the side I'm talking about the length of the actual 2X4 is about 6 1/2 feet. I'm not sure what the roof pitch is but it's steep, I can't stand on it without sliding down, much steeper than 12/12...I'd guess more like 16 or 18/12

As for the roof construction, from what I can see on top of the 2X4's are 1X6's running laterally, spaced about 16" on center. On top of those are cedar shakes. I'm not sure if there is plywood above that or not. It's now an asphalt shingle roof, less than 10 years old.

Oh, also there is no ceiling right now, it's open. The 2nd floor was partially gutted so I'm working with kind of a mess. They used to be Plaster and Lath and some rooms still have that present.
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Old 11-05-2007, 07:22 AM   #4
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Insulating slanted ceilings (hot roof?)


Whatever insulation you put in, consider stapling radiant barrier to the underside of your rafters under your cedar shakes... radiates that heat right back upward away from your attic and out your roof vents... you do have ventilation?
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Old 11-05-2007, 08:00 AM   #5
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Insulating slanted ceilings (hot roof?)


Quote:
Originally Posted by leezarrd View Post
Whatever insulation you put in, consider stapling radiant barrier to the underside of your rafters under your cedar shakes... radiates that heat right back upward away from your attic and out your roof vents... you do have ventilation?

Negative.....that's my dilemma. If I had roof vents I'd just put some proper vent and fiberglass and be done. That's why I'm exploring (hot roof) options. Spray foam insulation would work from what I've been told and what I've read but it's about $350 for 200 sq. ft at only 1" thick. That's going to but me way over budget. I'm wondering about those 4X8 polystyrene panels (or whatever they are made of) with the foil backing on them. Maybe I could put those between the rafter and seal all the gaps with cans of expanding foam.

Also, to correct myself above....the rafters are 16" on center, the 1X6" boards are about 8" on center

Maybe I can get a picture on here for you guys
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Old 11-05-2007, 08:07 AM   #6
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Insulating slanted ceilings (hot roof?)


Here's a picture of what I'm talking about, I took this last weekend and just cropped it to show you what I'm talking about, I can get a better picture if I need to. The slanted ceiling is where the red arrow is pointing to. I'm going to take those laths down if I can't do blown in insulation (which I'm 99% sure I can't) Maybe this will help you guys brainstorm some ideas for me. THANKS!



OMG, I just realized looking at that picture that those appear to be 2X6 roof rafters, it's the ceiling rafters going across the top that are 2X4....DUH. Sorry for the confusion I haven't been up there in a few days =)

Last edited by Skydmark1; 11-05-2007 at 08:10 AM. Reason: I'm an idiot
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Old 11-05-2007, 11:35 AM   #7
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Insulating slanted ceilings (hot roof?)


Since the insulation requirements are around R-49 in your state, I would try to get as much as you can in there. You could bump out the roof rafters and put in either R-19 or R-25 leaving at least an inch for air flow. Then install foam board across the rafters topped with at least 1/2" sheetrock. Insulate the entire room envelope similarly. You won't get R-49 anyplace in that area, but decide on the compromise that works for you. If you use the foil faced foam boards, tape the seams with the foil tape and use unfaced batts. Only one vapor barrier is used.
Install vents on the roof and the soffits to properly vent the roof . Keep the bays open from soffit to the ridge line.
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