I must be missing something. SIPs are insulated. So why (and where in the walls) would you put extra insulation?

If you're not using SIPs, the insulation levels you mention are sufficient, according to the recommendations of the U.S. Department of Energy (scroll down to map).

Worthy - Our builder used the foam board product instead of plywood or OSB traditional sheathing. It is not the 3-4" thick sandwich product I think you are referring to. So we will still need wall cavity insulation. Thinking about upgrading but not sure if it is worth it in the long run.

CC

Thanks for the link BTW.

CC

So it's stuctural foam sheathing. I've had success cladding with non-structural foam sheathing and fg batts. Properly detailed foam board is so tight already, I don't know why you feel you would need flash and batt too. But even as is, your house may be tight enough to benefit from an air exchange system. BTW, that's not a negative! But adding insulation alone is not enough to make your house tight.

Contractor shall provide and install full fiber-glass batt insulation in all exterior walls 9R-13), exterior overhangs (R-19), garage ceiling below conditioned second floor space

FG is a waste of time and useless above a garage with a room above.

The only effective way to insulate this space is with spray foam of at least R-19 in your climate. The rims too should be sprayed. Same with the basement. It costs a bit more. It's worth it. See Link below.

Here is a link that might be useful: Make It Warm

Thanks again Worthy. I appreciate the input and the link. Using the SIS Sheathing do you feel standard FG Batt is good enough? I agree that the Flash & Batt is too much. Do you have any thoughts or opinions on the BIBs system? As it is described to me - plastic sheeting across the studs and then blown in insulation. Will we see any benefit to justify the increased cost? How about going to R49 in the attic?

Merry Christmas and thanks again.

CC

The US Department of Energy link above says R49 for the attic falls in the "cost effective" range of attic insulation.

Dr. Lstiburek of Building Science Corp. calls for R60 for anything above the Mason-Dixon line.

The Bibs system, which has been around for at least 20 years, certainly looks like it should perform better than batts. But so much depends on the skill of the installers that I'm not sure there is a definitive answer. FWIW, I've been satisfied with high density fg batts for the walls, sprayed cellulose in the attic, fg and xps or sprayed foam on the inside basement walls.

Is that the sound of tiny reindeer feet I hear upon my roof?