Climate Zone 7A Build
Hello everyone. I am a long time reader of this site. I am planning a 1200ft2 addition and am looking for suggestions and advice. It will have a walkout basement with ICF walls. Some considerations to keep in mind. We are located in NW Ontario. Many of the specialty and higher performing building materials are difficult to obtain and are quite cost prohibitive. My goal is to do the best job possible using readily available materials. Following are areas I am looking for input.
#1. Wall assembly: I am planning at this point to use a double stud wall with a 2×6 structural exterior wall and a 2×4 interior wall insulated with mineral wool batts. I do not have dense pack cellulose available locally. I am contemplating the effectiveness of using 1 or 2 inches of polyiso as an air/vapor barrier between the two walls. I am also open to suggestions on other wall assemblies that are easy to construct from commonly available materials. I would like to end up somewhere in the range of R35-40.
#2. Heating: The house is currently heated by an outdoor wood boiler through an old air handler. I would prefer to stick with hydronics because that’s what I have already. I am planning radiant slab heat in the basement and either in-floor radiant or panel radiators on the main floor. I would like to integrate an air source heat pump for cooling as well as heat during the shoulder seasons. An ERV is also in the plans. I would like the system to be able to run off a high efficiency wood boiler or ATW heat pump in the future after the OWB gives up. Our sources of heat here are wood (readily available), electric (somewhat reliable), and propane (expensive). Heating degree days are 6000 at 18*C and 1% design day is -40C/F.
Any thoughts, suggestions, things I for sure should not do? I have done some reno work, but this is the first big project for me.
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Replies
1) R35-40 is perfectly obtainable in a double stud wall. 2.5” of space between the two walls with a framing factor of 23% and cellulose R value of 4 should give you an effective R39. If you want more, just widen the gap between the two stud walls.
nadroj,
I think you are on the right track. Double walls mimic standard construction pretty closely. Frame it much as you usually would including the roof, add the rigid foam to the inside, and frame the interior walls (1/2" shorter) tight to it, and you are done.
My main advice would be to draw. The more you draw, the less surprises later. Sections through where the ICF meets the wood framing, through the window openings, where services run, etc.