Hello —

I’m planning to build a SIP house in Northern California next year. We’re working with a potential GC (currently being paid hourly for drafting and design). We started with a design we liked, and have worked with him to refine. He’s just passed the design on to a structural engineer. I’m growing concerned that although both of them have SIP experience, they are approaching the project as a standard design that happens to use SIP walls and roof. But maybe this is a realistic approach?

Current question has to do with floors. The house is about 30′ x 35′, 2.5 stories over a crawlspace. GC is planning to build standard platform floors for each level. I asked about hanging the floors (either from the middle of a jumbo panel or off the top the wall below) instead. From my mostly outside perspective, it seems stronger, simpler, and tighter. GC and engineer are advising strongly against.

Engineers comment:

One item he mentioned was you interest in full height SIPs with the second
floor ledgered on, so don’t include that question. That is problematic as
the manufacturer’s tested shear panel assemblies (from which they derive
allowable loads) do not address this condition. To do it I would have to
spend who knows how long to research an answer the use of an alternate
assembly to those approved in the ICC-ES report. I honestly don’t think
it’s worth the effort but if you want I’ll do it…it’s your money.

GC’s comment:

You should feel comfortable with [Engineer]. He has more sip experience than any engineer I have worked with. Very few builders build with jumbo panels and hang the floor because while they seem like a good way to stand a wall quickly they have more draw backs than benefits such as the are a bitch to get on site and stand up ( you will need a crane instead of two guys), and they leave no room for any electrical/ mechanical. We need need those areas. And remember all the trades are still building traditionally so we can’t build to much out of their current practices or what you think should be saving you will cost you more down the road. As they say don’t jump over a dollar to save a dime!

It’s not that I feel particularly strongly about the floor construction, but I’m worried it’s a red flag. I have limited experience (oddly slightly more with SIPs than standard structures) but from reading this seems like a fairly standard practice. Morley suggests it, and several panel manufactures detail it in their design guides. The “who know how long” implies to me that it’s not an approach that the engineer is familiar with. Yes, it would require a crane, but so will the SIP roof. On the other hand, perhaps the GC is being realistic that pushing the envelope (wherever it happens to be) is not a good strategy.

What do you think? Are they being pragmatic, or stuck in the past?