Foam Insulation in Attic Rafters

happycthulhuMay 15, 2008

I've been thinking about having foam insulation blown into the spaces between the rafters in my attic.

The attic floor is insulated with cellulose, and the attic is open to the outside with a couple of whirly-gigs and two gable vents.

Would insulating the rafters give me any benefit at all?

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No, if the space above the current insulation is ventilated to the outside, then you won't get much of any benefit out of insulating the roof rafters.

It would be better just to add more insulation on top of the current insulation. Blown in cellulose works well and is cheap and easy to do.


    Bookmark   May 15, 2008 at 6:14PM
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search for info on unvented attics
lots of foam insulation companies sell a 'total enapsulated' attic package.
best of luck.

    Bookmark   May 19, 2008 at 4:41PM
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foam....a good way to rot your roof deck and trusses

    Bookmark   June 11, 2008 at 9:09PM
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Ok, well I guess that's nixed that idea.

How about insulating under my wood floors in the crawl space?
Would that help my energy costs any?

    Bookmark   June 12, 2008 at 10:58AM
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You would need closed cell foam sprayed in your crawlspace.

    Bookmark   June 17, 2008 at 12:30PM
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Can't tell where you are located from the pics of your house, but if your concern is summertime heat gain you might consider radiant barrier installed on your rafters. It will help considerably in the summer. But to have any positive impact in the winter it needs to be installed right over the existing insulation and it looks like a large section of your attic is floored and you use it for storage.
You can google radiant barrier and find plenty of sites that show how to install. It should be a pretty easy diy project in that attic,

    Bookmark   June 20, 2008 at 2:47AM
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You do not say where you are or if you have heat/AC ducts in your attic.

You can use styrofoam panels with a foil heat barrier installed on your rafters.

Those whirly-gigs are useless. I had mine removed when we put on the new roof.

The conditioned crawl space is a great idea. Close your vents off.

    Bookmark   August 22, 2008 at 2:02PM
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Our ducts are in the crawl space.
I can't close off my crawl space though because my house is balloon framed.
I can look up from inside the crawlspace all the way into the attic because of the space between the outside brick and the wood frame for the interior.
The cold air would just flow up into the attic and out the vents.
As for whirly-gigs, ours work real well.
We have two of them plus gable vents and it's cooler up there than it was before we had the whirly-gigs installed.

I wonder if styrofoam panels with foil would be a good idea for between the floor joists in the crawl space?

    Bookmark   August 22, 2008 at 2:17PM
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Hi Happycthulhu. Yes! Spray foam insulation would do a tremendous job for your application(s). I provided a link below that has good information for anyone interested.

Here is a link that might be useful: Spray Foam Insulation

    Bookmark   February 10, 2013 at 9:16AM
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Spammers dig up old threads.

There is lots of bad information in this thread. Nothing good can come without climate/location information.

    Bookmark   February 11, 2013 at 8:07PM
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Windows on Washington Ltd


Hopefully future readers will not get steered in the wrong direction.

Get to Building and get educated folks before you invest big money in SPF.

    Bookmark   June 12, 2013 at 11:03AM
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Two years ago, I had foam sprayed into my roof, trying to live more comfortably. This did not seem to be helping so I installed 3 whirly gigs thinking it would ventilate the attic. This is an older home. After reading some posts now I don't know what to do. I'm older but I climbed into the attic and put styrofoam in the openings to close them, now I'm worried if rain will come into the opening where the WGs are! Input please!!

    Bookmark   August 7, 2013 at 9:13PM
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Cap them from above.

    Bookmark   August 11, 2013 at 8:11AM
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Windows on Washington Ltd


If the roof is now insulated, pull the attic vents and close them up.

    Bookmark   December 10, 2013 at 8:13AM
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