The SIP manufacturer should have one or more structural engineers that they work with on a regular basis.

yes, we are trying that angle. They've put in a lot more hours than we have given them $$ for, so if they can't come up with an engineer for us they know there's a good chance we'll walk. However starting fresh with another company will also delay us even more. @Charles Ross Homes we thought they were going to engineer it. We fired our first sips company that couldn't deliver on time and switched to these guys, but it wasn't clear in their bid that they don't do the actual engineering. Supposedly they are giving us a name of a company, but the clock is ticking and we need this done soon.

Call your local division of inspection and see how fussy they're going to be please.

What I'm getting at is:

Its time to build a few days after the slab is poured. If your structural engineer specified 2x6 exterior walls 16 OC you can sheath & fill with foam. Same with roof. The performance would be comparable.

IMHO, windows are most of the energy loss problem as they're usually between R3-R4 unless they're triple glazed.

Lumber looks like it will increase in about 30-60 days due to futures, so consider that added cost. Also, your money sits and/or your construction loan incurs interest while you make no progress. If you have a construction loan, it may need to be extended. That is also a cost to consider.

"...we thought they were going to engineer it." The third-party engineering cost should have been a separate line item in the SIP manufacturer's proposal.

bmanning What product did you end up going with?

@kelly roberts we used Thermocore for the panels. They don't do the engineering and the company they referred us to was also too backed up to do it. We ended up using the engineering firm that did our timberframe engineering, Tamarack Grove. They were wonderful to work with, wish we could have used them for the entire project! I can't say I'd recommend thermocore, there have been a number of issues aside from the engineering. Possibly the complexity of our roofline made this a project that was not sips friendly, but they took 5 months to design the sips and then what arrived does not fit together as it should. The measurements on many panels do not match the shop drawings so the guys are having to cut the panels on site to make them fit. Given all of this, there really has been no time or labor savings by using this product. I'm just hoping we get a warm house out of it.