Deciding between blown-in or spray foam attic insulation

13 years ago

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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Comments (3)

sautesmom Sacramento
13 years ago
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
kimkitchy
13 years ago
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.
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you are correct....open cell is the cheaper, less R and higher perm (allows more water through) then closed cell. Closed cell will be a added cost, but would probably be worth it in the basement at least. Closed cell, in general, will seal up your entire house better then open cell, as well as add structural rigidity to your 2x4 framing making your house stronger. Open cell does not. Closed cell is not water proof, as it seems your questions are hinting toward. Cellulose is just fine for the attic, and going with more closed cell is a waste of money IMO. An animal can rip apart open cell just as easy as getting into cellulose. Besides, if something gets in there you have bigger issues anyway! Also, your roof is suppose to be water proof....not your insulation. If your roof is failing, you do NOT want a water proof insulation anyway. This traps water and allows wood to rot, thus a possible structural failure in your roof without you really even knowing. You may also be money and r value ahead to practice air sealing your walls with caulk and then using a blown fiberglass or dense packed cellulose in your walls. A side note...spray foams are THE most expensive possible way to insulate a home, and most cases you will never see a ROI compared to dense packed cellulose and blown fiberglass with air sealing especially in your climate. (note, I never mentioned batts).
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There are gaskets you can get for cans and you can caulk the penetration with the trim off also. I'd do that first and see if it helps. The knee walls are a problem but I bet the cans are the real issue. Radiant barrier is not worth a retrofit usually. During new construction, the OSB with barrier is just a small upcharge. I think it was like $200 for our house and so it is worth it. I have a friend who had a similar house to mine built but with no extra insulation etc. He is having a similar problem as yours and he has gotten several quotes including foaming the rafters. His plans include finishing the attic someday (why I don't know since he has a finished basement and is over 6k) so he is thinking of foaming the rafters. I encouraged him to get his cans sealed - sorry I don't know what he did and summer is over anyway... It frustrates me to no end when I hear this story over and over. Comfort issues that are really failures of sealing and insulation. GCs are so oblivious to energy costs but the comfort issues should come back and bite them. Cans into an attic are just always an issue. They are so rarely handled ideally especially in the South. But you can get a lot of mileage from the gaskets and caulking the edge when you take the trim off. I bet you can fix 50% of your problem. You can certainly reduce air movement 80% but you can never have the space taken up by the can to be any better than r-2 that lowers your r-30 by a significant amount. If you can get above the can (and I am guessing you can't), then you can seal 100% and insulate some. The knee walls are an issue for 2 reasons which you probably already know. They often around here are a r-13 batt with no enclosure. Batts work pretty poorly when not enclosed in a space. Also r-13 wall against a 140 degree attic is pretty bad when you are trying to maintain less than 80 inside. The rigid foam encloses the batt, deals with the thermal bridging at the stud and adds another r-4 to the wall. It probably cuts the heat gain by 50% by a combo of all these benefits. It really should be code. The 4x8 sheets cost $12 or so.
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brickeyee
11 years ago
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.

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Deciding between blown-in or spray foam attic insulation

Comments (3)

sautesmom Sacramento

kimkitchy

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