I read an article that I found on green building advisor and all the knowledge I though I knew about insulation went out the window. Keep in mind I live in the Des moines Iowa metro and I want to build a house to be very efficient.
http://www.greenbuildingadvisor.com/blogs/dept/musings/cold-climates-r-5-foam-beats-r-6
Now I guess my question is after you put your sheathing should you put on a reflective polyiso board and then the rest of the insulation on the outside using xps? Would 2 to 4 inches of xps on the outside of the polyiso warm the board up enough to work efficiently as if it were in a warmer climate? Or is the cost just not worth buying the polyiso?
all thoughts greatly appreciated.
Replies
XPS alone will be fine
If you're going to put foil-faced polyiso over your sheathing in hopes of gaining a "radiant" or "reflective" barrier and then cover the polyiso with another material like XPS, there's no need for the foil. For the most part, a radiant barrier will only perform as a radiant barrier if there is an air space in front of it. A foil surface in direct contact with another surface simply becomes a conductive film.
So yes, you could omit the polyiso entirely and use two layers of 2" XPS with the seams staggered. Integrate them with XPS on your roof and you can create an excellent envelope.