I built an 800 sq foot icf single story addition with full basement. I have 9 foot ceilings and some is cathedral to 11 foot. My location is NE. Also I had 3 inches of 2 pound spray foam sprayed on the ceiling. My question is do I need more insulation? We had a few frosts this fall and I could easily see where each of my roof trusses were they were defined by a lack of frost in those areas. Also the foam was sprayed directly against the roof deck. I have plenty of room for more insulation, but can't afford anymore spray foam. My initial thoughts are to add a layer of R30 faced fiber glass directly under and in contact with the foam. I think I could use tie wire to hold it directly against the roof deck. I think I was over sold on the foam. I have found the space is not that easy to heat maybe it's because I have a bunch of windows for this small pace. In all about 13 windows and most are 3 feet by 6 feet in size. This looks nice but I'm not crazy about the heat loss. Any help with insulation ideas would be greatly appreciated.

Mike, I don't think you were oversold on the foam. You just don't have as much as you really need. The reason you see frost melted where the trusses are is because the foam must not cover them much allowing them to be in contact with the room air. Three inches of foam would barely fill in the space between the trusses. Whoever was doing your insulation design didn't spec out enough thickness. Cellulose would be a better choice than fiberglass.

But, that being said, air leaks are a real killer. You've got to get them under control. You can loose as much or more heat with air leaks as through the walls, roof, or glass. Get as good a window as you can possibly afford. To give you an idea of the part windows play in heat loss in my house, with 6" ICF walls and Andersen wood casement windows, each square foot of window was calculated to lose as much heat a 4 square feet of wall.

Your greatest payback will probably be in your investment in better windows. If it is at all feasible you may consider filling in some windows with wall. Not a palatable choice at this point but something to consider.

Awesome input, thanks. I don't have all my rough in wiring and plumbing that's why I am still considering insulation options. If I go celulose how do I support. Or do I just wait till I have drywall ceiling up and apply then?

Hopefully someone with experience using cellulose will chime in. I've never used it. Only built one house, ever, and it's the one I'm living in. Used only foam on the roof underside.

Is that the crushed paper like product? I have used it before. Just wondered why you choose that I've fiber glass.

Posted By Mike kline on 11 Dec 2010 12:04 AM
Is that the crushed paper like product? I have used it before. Just wondered why you choose that I've fiber glass.

Yes. If you can navigate the search function here without too much frustration, search on fiberglass. What you'll find are quite a few comments about fiberglass being very air permeable allowing air currents to move through it, carrying heat from one side to the other. Why are furnace filters made of fiberglass? Because air moves through it quite nicely!

I'm with dmaceld -- fiberglass is best for filters. Yes, millions upon millions use it but hey -- that's the power of marketing. Regards.