Icynene Spray Foam on Underneath Side of Roof Deck – Zone 5
After reading for months, getting 4 quotes from spray foam contractors in my area, and undergoing an energy audit, I’m in the process of finalizing plans for open cell half-pound Icynene application to the bottom side of the roof deck in the attic. This is a retrofit job. Within the attic is a furnace in a closed room vented directly to the outside. I have a few questions after I received the proposal today from the contractor
#1 – I currently live in Zone 5 (Chicago IL). I’ve received quotes for application of 6.5″” or R-23 and 10.5″ or R-38. The difference in cost between the two for the square footage I have is $12,500. Local code specifies R-38 for attics, however I’m unsure if this is applicable for all types of insulation, or conventional bat/blown cellulose. Assuming local code to not be an issue, how quickly (if at all), would I see the return on investment for the thicker foam?
#2 – The attic is unliveable space. There is currently a furnace room and heating vents running throughout the attic. Do I need to apply a vapor barrier to the foam after its installed? I’m not planning on covering the foam with drywall. The rafter bays are framed with 6×12’s.
#3 – The energy auditor recommended installation of an HRV due to alteration of the stack effect after the foam insulation. Is this reasonable? How would I test if I needed such a device? I’ve received a quote for installation of a Lifebreath RNC5TPD HRV system to be installed using the upstairs bathroom fan vents for $2,000..
#4 – The house has currently 3 furnaces (2 in basement – 1 supplying basement, 1 supplying 1st floor, 3rd furnace is in attic). Total BTU is 180,000. The house size is roughly 5,000 sq ft. After application of the foam, the house will likely be overpowered. Is this a consequence I’m going to have to live with, or are there any alteration that need to be done to the furnaces?
Thanks for any input anyone is able to give on these questions. Getting any valid opinions on these matters are helpful since there is often misleading and a wide variety of opinions people recommend.
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Replies
Kevin,
Q. "Assuming local code to not be an issue, how quickly (if at all), would I see the return on the $12,500 investment for the thicker foam?"
A. I'm shooting from the hip here, but $12,500 will buy a lot of natural gas. Unless energy prices go absolutely crazy, I can't imagine that you'll get a reasonable payback for your investment.
Q. "Do I need to apply a vapor barrier to the foam after its installed?"
A. Yes. You can spray vapor-retarder paint on the cured foam.
Q. "The energy auditor recommended installation of an HRV due to alteration of the stack effect after the foam insulation. Is this reasonable?"
A. There are a lot of variables that enter into this equation. The bottom line is, the best way to tell if you need more mechanical ventilation is to see if you have condensation on your windows during the winter and to pay attention to odors and stuffiness. If you don't have condensation, and it your house doesn't seem stuffy or smelly, you're probably OK.
Q. "Are there any alterations that need to be done to the furnaces?"
A. The next time one of your furnaces conks out, don't replace it without having a heat-loss calculation performed. Once you know your design heat loss, you may be able to eliminate one or two of your furnaces.