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Old 04-28-2014, 03:36 PM   #1
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Insufficient Insulation and AC Equipment in Attic

I'm in Southern Louisiana (i.e. humid and hot 9-10 months out of the year) and have a 3,200 square foot house (~2,200 sq ft. of attic floor) with very poorly done R19 fiberglass batts in the attic. All of my AC evaporator coil and ducting is in the attic space. Energy bills are in the neighborhood of $350 total (Gas + electric) per month which is quite a bit more than double what our last 1,900 sf house (Which was well insulated with cellulose and had a lot more shade). Here are the options I've come up with:

1) Seal up the ceiling and wire penetrations as best I can myself (I've already started this), and have someone blow cellulose over the bats. $945. I could blow it myself but it's like $800 for the materials through retail stores.

2) The same as #1 except with Rockwool. $1,150

3) Have 3-6" of open cell foam sprayed on the underside of the roof sealing up the attic space. $4,375-5,600. Get rid of the existing bats?

With option 1 and 2 I'd probably need to improve my insulation on my ducting. I have some 50' long duct runs and when the AC kicks on it blows all of that hot air that's built up in the ducts out for a few seconds before the cold air displaces it. So, I get a big blast of attic hot air into the living space each time the system cycles. I could go R-50 on the ducting but it's not going to be cheap to buy and install all of that.

One other factor is that they house had a bit of a mouse problem in the past. A lot of the batts have mouse poo on them. Options 1&2 require some cleanup of this mess by me (It's not too bad) and would be quite a bit more expensive if I wanted to ditch the bats all together. I'd love to just roll up the bats and trash them all. I'd retain some of the good ones and put them over my garage.

So, factoring in all of that and making an "apples to apples" comparison spray foam is a bit over double the cost but would also mean less DIY labor vs. the conventional insulation options.

I work at a university down here and it seems that all of the building science instructors/professors are big on the whole sealed, "partially conditioned" attic space thing for our climate.

I'd like cheap but I'd also like to have an attic space that's less rodent friendly while simultaneously making my AC system perform a bit better with the spray foam. I'm not too concerned about the potential for a 10% reduction in shingle life. Does anyone have anything else I should consider here?


Last edited by JeffW650; 04-28-2014 at 03:39 PM.
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Old 04-28-2014, 08:50 PM   #2
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Your call. You have the options pretty well sorted out as well as the pluses and minuses.
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Old 05-02-2014, 11:56 PM   #3
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Did you read these?,d.cGU&cad=rja

PS. one more, need to search my library, miss-filled...
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Last edited by Gary in WA; 05-03-2014 at 12:13 AM.
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