Explain Foam Insulation and Attic Ventilation over different spaces
HU-412631568
2 years ago
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Mark Bischak, Architect
2 years agoSeabornman
2 years agoRelated Discussions
Deciding between blown-in or spray foam attic insulation
Comments (3)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....See MoreExpanding Foam Attic Insulation
Comments (11)"Because sprayed foam can cost 5 X ore than conventional fiberglass or cellulose." This is a gross exaggeration for what the OP has described. The OP has not described the attic conditions very well or the foam he is asking about so I will assume it is a low slope truss system with restricted access and therefore the foam insulation proposed is probably a 1/2 lb density polyicynene free rise open cell expanding foam (60 to 1). If so, this material is water vapor permeable, doesn't wick water, and has an R value of 4 per inch per s.f. It should cost 1.5 to 2 times the cost of fiberglass if sprayed in a wall. I don't know what the cost difference is when poured into an attic space. If the attic is to be ventilated it might be difficult to install eave vents that are not blocked by the foam. It is likely the attic would be sealed....See MoreInsulating the attic - spray foam?
Comments (23)I'm glad to come across this thread because I'm also trying to figure out whether/how to add blown-in insulation to our attic, and possibly radiant foil. I hope I'm not derailing the thread by tacking on. Our home is a roughly 120 year old Victorian, and it also has a sprinkling of old insulation in the (sealed) attic, but nothing more. And when I say attic, I should clarify--we actually have a finished attic/third floor but the very peak of the attic, above the ceiling of the finished area, is unfinished. It's like a capital A, where the lower half is the finished portion and the upper half is unfinished. I'm sure there's proper terminology for that but I don't know what it's correctly called. We use the finished portion regularly, or at least we would if it didn't get very hot up there in both the winter and the summer. In the winter, we can counteract this by closing the HVAC vents so the attic is only heated by the hot air rising through the house, and that works well enough. But in the summer, we add two window units in addition to the house AC (to cool a space that's probably 400 sqft)--the window units are kind of a mixed bag because with the way they're installed, they let in a good portion of hot outside air around them through the window. We're contemplating replacing the window units with a minisplit system in the attic alone, but I feel like it's worth exploring all the various possible ideas to try to keep summer heat out of the finished portion of the attic before installing a whole new additional system. Any thoughts or ideas for me?...See Moreattic wall covering after foam insulation
Comments (26)From the photos, it appears that you've constructed an unvented (conditioned) attic-- which, as @The Cook's Kitchen pointed out--by definition, does not require ventilation. I'm a proponent of conditioned attics and crawl spaces and the use of spray foam (SPF) insulation in their construction. The construction details vary by climate zone and application. I strongly encourage anyone interested in designing and constructing an unvented attic or crawl space to consult a local building science professional and your local code official before doing so. Now, back to the OP's situation.... Depending on the specific spray foam insulation installed, the application thickness, and other requirements, a prescriptive thermal barrier or ignition barrier may not be needed to comply with the applicable building code--yes, really! You'll need to refer to the Technical Evaluation Report (TER) for the particular insulation material to see what is required in your climate zone....See Moremojavemaria
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