Deciding between blown-in or spray foam attic insulation

anniehgwNovember 11, 2010

I live in a 1945 brick colonial in Northern Virginia. As soon as the temps go down, you can really feel the cold in our upstairs. We've started looking into improving the attic insulation and now I'm totally confused. This house is small with minimal storage space. The attic is floored and is one of our main storage spaces, and there is already insulated under the attic floorboards, but it is only about 5-6 inches high. Best guess is that our current R-value is around 10.

We've had a few insulation companies give us estimates. The main question is how do we keep the storage space and raise the R-value of the insulation???

One way seems to be to make the attic a conditioned space and spray foam along the slope. The attic will then be conditioned and completely closed and unvented (oh yeah, old home with just one vent at one end and an attic fan at the other. No soffits or ridge vents).

The other alternative we've gotten is to blow in insulation to build up the insulation around the edges of the attic that are not floored in and then just leave the floored area as it is.

The price difference is significant. Spray foaming is 3x the blown in. But what about the attic being unvented? What about air sealing? The spray foam guy explicitly included air sealing in the estimate and discussed it as an issue.

At this point we don't know how to make a decision. Make the attic a conditioned space w/spray foam or just improve what insulation we can?

Any advice greatly appreciated!!!!

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If money were no object, I would get the sprayed-in. But, since money is tight for me right now, I have been recently looking into the price of adding more blown-in cellulose. At Home Depot you get a free blower rental with 20 bags, which would cost around $200. I would say spring for the $200 this winter and blow in more insulation, and see how effective it is. You would probably at LEAST get your $200 back in reduced heating bills.

But, if it doesn't do much, next year get the spray foam.

Carla in Sac

    Bookmark   November 11, 2010 at 3:06PM
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It seems to me that you should answer two questions. Do you want conditioned space in your attic? How much money are you willing to spend?

Our story: In our 1/2 story remodel we have conditioned living space. It had always been living space (at least for 70 or more years of our home's 97 years). During the depression there had been vermiculite in the space above the ceiling. In the 1950's parts of it got fiberglass bats in the space above the ceiling. (It had always been finished like an after thought, pressboard walls, and even cardboard over 1xs during the depression!) When we gutted the poorly finished space, we decided to have cathedral or loft type ceilings. Our roof does not have any vented soffits, nor a ridge vent either, so we had to have spray foam insulation in order to do the cathedral ceilings and have some kind of insulation. It did cost a small fortune (in our estimation), but it is highly effective. Between that and foam backed roof sheathing we have a cold deck roof. Unless the snow load is wet/heavy, we don't have to shovel it; the entire roof melts evenly with virtually zero icicles and no ice dams. The 1/2 story space needs very little heat, there is more sound proofing to the outside than before, and this will sound odd, but the foam literally glues your house together. Kind of hard to describe. Our space has been inspected by structural engineers, don't worry! But before the foam was sprayed you'd arrive at the top of the stairs and walking in certain spots created "creaking". After the foam was installed, no more creaking. We are very satisfied with spray foam. YMMV

Others who will post here clearly prefer blown in cellulose. Since I have no experience with that type of insulation, I hope they will post about it. Hope you get the information you need and end up with a space that meets your needs.

    Bookmark   November 11, 2010 at 4:11PM
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Do a search on 'flash and batt insulation.'

It uses a thin spray foam layer to seal and insulate (up to the dew point in the layer) and then less expensive batt insulation for the balance of the R value.

    Bookmark   June 14, 2012 at 2:07PM
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