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jim_arnau 11-06-2007 01:39 AM

Attic Insulation

I need some help coming up with a cost-effective solution to insulate my the attic in my cabin. I currently have no insulation overhead. There are exposed rafters overhead in the living space. A layer of pine boards form the ceiling over the rafters, and also the floor in the attic. The rafters under the roof are exposed in the attic.

I want to come up with something simple that I can do myself. Can I just roll out insulation onto the floor of the attic? As I said, the rafters are exposed in the living space rather than in the attic, so if I roll out insulation up there, the rolls will butt against eachother rather than against a rafter.

I thought about installing the rolls of insulation between the rafters on the roof, but this seems complicated with ventilation / moisture barrier concerns.

What's the easiest effective way to do this?

Ron6519 11-06-2007 07:21 AM

You can roll the batts out on the floor. You just lose the ability to use that space due to the insulation. You could also use foamboard on the floor and cover it with plywood, still giving you the ability to use the space. I guess you didn't want to put it in the rafters under the floor for a reason?

NateHanson 11-06-2007 08:14 AM

I think you want to roll out some poly sheet first, to provide a vapor barrier on the heated side of the insulation. Then just roll out unfaced fiberglass, or blow in cellulose. It might be cheaper and easier to do cellulose.

Foam and plywood would be the most expensive solution.

jim_arnau 11-06-2007 09:35 AM

Thanks for the advice.

Does anyone have a rough idea of the costs of these types of insulation (foam and batt)?

For the poly vapor barrier, does this need to be specifically designed to block vapor or can a standard poly sheet work? Do you just duct tape the seams together?

Do foam panels provide as much insulation as batt?

I'm not sure why but I'm a bit hesitant to go with blown-in. Seems like a messy job, and a messier job to undo if I ever wanted to.

jim_arnau 11-06-2007 09:38 AM

Yes, there is a reason I didn't want to put it in the rafters. The place is a log cabin with exposed rafters and a wood ceiling overhead in the living area. I didn't want to put the insulation between the rafters because I would have to cover it with wood or sheetrock to avoid seeing the insulation...a much bigger job.

NateHanson 11-06-2007 10:21 AM

Rigid foam costs about $25 for a 4x8 sheet of 1.5". It's R value is 5 per inch, so to get R-30, you need 6 inches. It's really not a practical way to insulate your attic.

jim_arnau 11-06-2007 12:28 PM

I found R-30 Kraft faced with a vapor barrier at Lowe's for 67 a roll. (88 sq ft. coverage.) At that rate, I think the whole job should cost about $750.

My plan is to heat the cabin to 45 degrees for the winter, only turning it up when it's in use. Do you think that R-30 is adequate for that application?

NateHanson 11-06-2007 01:29 PM

That depends entirely on how much of a furnace/heater you've got, where you're located, and how much you're willing to spend on heat.

Ron6519 11-06-2007 03:28 PM

"My plan is to heat the cabin to 45 degrees for the winter, only turning it up when it's in use. Do you think that R-30 is adequate for that application?"

What about the rest of the structure? Insulating is not a one aspect situation. Walls, floor, windows and doors play a part. As Nate said, where you are in the counry will dictate insulation guidelines. You'll spend less on heat with the insulation, but will R-30 in the attic get you where you want to be?

jim_arnau 11-06-2007 03:58 PM

It's in it's pretty frickin' cold!

I think the house has insulation in the walls, but none inside the frost wall or in the attic. I have storm windows on the whole house, and the doors are pretty tight. Over time, I'll put some money into insulation and more efficient heating systems, but for now, I need to pick the low-hanging fruit.

I figured the attic would be a good place to start. I'm hoping that going from R-0 to R-30 will make a big difference in heat costs (maybe 20%). Is that a reasonable expectation?

NateHanson 11-06-2007 07:51 PM


Originally Posted by jim_arnau (Post 72071)
It's in it's pretty frickin' cold!

THAT'S the truth!! :eek:

I agree that insulating the attic is a great place to start.

I'm a little skeptical that the walls would be insulated if the attic was not insulated at all though. Even so, the attic should help a lot. I have no idea exactly how much.

Where in Maine? We talking Aroostook County? Or Kittery? The difference can mean 30 degrees sometimes.

What sort of heat do you have?

jim_arnau 11-06-2007 08:32 PM

I'm in Naples, which is the northern tip of Sebago Lake. Not the coldest part of Maine, but I wouldn't exactly call it the tropics either. :wink: Where are you at?

I have to pull a couple of outlets to see if the place is insulated in the walls next time I go up.

I have forced hot air / oil burner in the crawl space. There's also an open fireplace. I found an old woodstove in the crawlspace that I plan to refurbish and install in the hearth this fall.

The place is hardly energy efficient at this point, but like I said, I just want to get the big loss points taken care of this year.

Ron6519 11-06-2007 09:48 PM

I would address the open fireplace. You can lose a boat load of heat up the chimney. Even the best flue damper is nothing to write home about.

NateHanson 11-07-2007 08:59 AM

Yeah, I'd make a rigid foam cutout to fit tightly in the opening of the fireplace when you're not there.

I'm up by Acadia NP.

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