Hi John-
There are certain laws of physics which need to be obeyed when building a pool enclosure which might be more boldly flaunted in a less extreme environment. I'm sure it's old hat for you, but moisture drive is the most critical one to understand. Water seeks it's own level, and so a warm and humid environment indoors has water vapor in it that wants to get out side, where it's cooler (and therefore dryer- cool air can hold less moisture than warm air). In the PACNW where you are it's perhaps less critical than in the upper mid-west where I'm from, as the temperature differential is much greater- but none-the-less it's important no matter where one builds a pool enclosure.
I have found the books by Joe Lstiburek, specifically "Building in Cold Climates", to be particularly helpful in understanding how the laws of physics work when building, and what the consequences are when they're not. I believe Amazon has them.
Thinking about SIPs specifically, the EPS core has a very low perm rating (not sure about iso cores- never used 'em..). The area that needs to be payed particular attention is the seams, or joints. If the expanding foam is not injected in to the joint thoroughly and correctly, a void could result; this area is thereby underinsulated and undersealed, allowing moisture vapor to enter and, when reaching a cold surface (such as the outside SIP skin), condense in to water. Water and OSB is a bad combination. Trouble is it's difficult if not impossible to know if you've done a good job without destructive testing.
In any heating climate, the strategy should be to adequately seal the SIP joints on the inside, so water vapor has no chance of entering. This can be done with strips of adhesive membrane (such as Ice and Water Shield). Insulspan uses the strategy on their roof SIPs. The wall to roof connection is also critical, and can also be covered with Ice and Water Shield. Working around timbers is tricky, but possible. Walls can be covered with a vapor barrier such as 6 mil poly, being careful to detail the edges, overlaps and penetrations carefully.
It should be noted that any wall system needs to be detailed extremely well when inclosing a pool. SIPs have the benefit of being tight- and the Achilles heel of concentrating potential shortcomings at seams, where they may go undetected until things have progressed beyond the point of no return.
In addition to sealing the SIPs well, HVAC needs to be detailed and executed by someone who thoroughly understands the building science. This is no place for the low bidder.
IG windows should be used as a barometer. If they are condensating consistently, indoor humidity levels are too high.
Hope that helps. I've been down this road once or twice..
Chris Koehn
