Timber size for SIPs construction

[mr rusty]

Hi. I'm going to be building a substantial garden room using SIPs from simply sips. Their 122mm panel is 100mm core with 11mm OSB either side. Obviously in some places rather than splines, I will use timbers slotted in to the sip rebates. - wall plate, sole plate, corners, round window frames etc.

 

My question is that if I go and buy my usual 100x50 carcassing timber it's more likely to be 95 x 47. How critical is that 95 v the 100mm rebate? Would I be OK foaming the timbers in and taking up the gap? or should I perhaps be thinking buying "125 x 50" and running it through the saw to exactly 100mm?

 

Another alternative that springs to mind is to use 100x100 fence posts, which are exactly 100 and run them through the band saw into 2 100x50's, but fence posts are not kiln dried, although in my experience tend to be very stable.

 

Thoughts and recommendations from people that have used SIP's?