Foam insulation in existing walls - good idea?
pompeii
16 years ago
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bry84
16 years agopompeii
16 years agoRelated Discussions
Basement with Existing Stud Walls - Insulation Options
Comments (4)1.5-2" is the 'norm' in climates similar to mine, but not sure if there's a definitive resource on this. That's on the wall. But the total R Value should be higher. And that can be achieved with lower cost fibrous insulation or EPS (expanded polystyrene) added between the studs. Another alternative--in cold or mixed climates only--is the use of a MemBrain "smart" vapour retarder with fiber insulation. Of course, any system composed in part of moisture sensitive materials is at risk from groundwater....See MoreFoam insulation in attic/ blown cellulose in wall?
Comments (4)I don't want to hijack your thread, but I have the exact opposite question! We are thinking of air krete foam in our existing walls and blown in cellulose in the attic. Is the air krete (a cement based foam) much better than dense pack cellulose in the walls? It's about $1200 more. Any help with insulating info would be greatly appreciated. We currently have next to none in both attic and walls. Thanks....See MoreInsulating Exterior Wall Cavity on existing house
Comments (1)They can put a slow rising foam in the walls , but it can be very expensive. with foam you would need no vapor barrier. You can go with cellulose and paint the walls with vapor barrier paint. Here is a link that might be useful: vapor barrier paint...See MoreRigid Foam Insulation on outside walls
Comments (25)Here's a bit more info to give you a better idea. Zone 5B, Cold winters, hot summers (rarely humid but like this year...humid and hot summer!) My walls will be 2x6 with either dense fiberglass or mineral wool insulation (products readily available locally). My current debate among my thoughts is trying to decide about the WRB (MY HOUSEWRAP) and at what tier/level/plane to install it (Or even two). Windows are not permanent, and in a forever home (God willing), windows will need to be replaced in the same lifetime I live. Therefor, I don't want to choose some method that would hinder future upgrades/replacement. (Such as installing foam over a flange so it must be cut out, or installing a type of flashing that requires more of the foam wall or window box to be torn out to replace the next time around. I am debating between a quality house wrap to prevent moisture and also act as an *air* barrier not a *vapor* barrier. Basically, on a cool winter day with 50 MPH Wind, I don't want that wind (air) easily permeating through the house because I will a.) not be sealing the joints of foam b.) possibly not even taping the foam joints c.)not going to use any internal poly as a air or vapor barrier. I am not sealing the foam joints because foam shrinks and expands and those joints will not stay tight forever. If I have the luxury, I will install (2) layers of 1" thick versus (1) layer of 2" thick to provide staggered joints and prevent air from moving inwards that much more. There is a wealth of information on greenbuildingadvisor, but it seems to boil down to personal preference on two things. One being that I can opt for innie (windows set towards the OSB wall sheathing layer) or outie (windows that are at the most exterior plane as possible). And we all know that flashing a window opening is important for multiple reasons, and that the standard way includes integrating your house wrap (WRB) into the rough opening with multiple methods. I would like to use a flexible peel & stick flashing that will seal to/against the house wrap. My concerns for those who have rigid foam on the exterior are a.)where did you locate a house wrap (Or WRB)? and b.)in what fashion did you set your windows? It varies by foam thickness, but generally 1.5"+ of foam requires framing out a window frame/buck for window support whereas under 1.5" doesn't seem to need the additional support. And of course the other option is the fasten the window like standard construction, on the sheathing level right against the sheathing (osb in my situation) and into the studs. This would then mean I would either use the WRB at the same time to detail the window opening, or perhaps not. But also means I would have to design a custom flashing to cover the exposed foam around the window, since the window is set inside from the foam and siding. I am surprised house wrap (a WRB) seems to not be the norm. It is here...and it is something I do not want to overlook. My understanding is that in new construction with rigid on the outside, builders extend the window opening (like you said Mushcreek) to the same thickness as the foam, therefore that foam will not have an exposed edge. I read on GBA that instead people build plywood boxes for the windows the thickness of the foam + 3/4" and then use a 1x3 or 1x4 flat around the window opening fastened thru the foam into the window opening studs. Then the window flange is fastened to this flat 1x3 or 1x4 frame, and it also brings the window out the extra 3/4" so that 3/4" firing strips can be used to install siding. I do not think house wrap *over* the extended window frame would be as effective as if I just installed the windows flush with the foam level, allowing my flexible sticky flashing tape to easily fold over the opening and adhere to the foam. ---starting to think I should just not be so concerned about this detail. Turning my hair grey....See Morepompeii
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