I've seen various foam products deteriorate over time, becoming crumbly, etc. I'd hate to build with SIPs and have the house crumble 20 years down the road. Barring something like flooding or getting saturated by a plumbing or roof leak, how long will SIPs last? Are there any known causes of SIPs deteriorating unexpectedly, (spilled solvents or cleaners, ozone, etc)? I see many SIPs have OSB on the outside and wall board on the inside. They have wiring chases built in. What if the wall board becomes damaged, (like if you wall paper it and botch the removal or get mold in a bathroom or a grandfather clock falls oner and gouges it)? In traditional frame building, you could rip out the damaged wall board and replace it, but I don't see that as an option with SIPs. What do you do if you want to add or move light switches and plug outlets on an exterior SIP wall? When the SIP has OSB on both sides, I assume you frame out and sheet rock the inside. Of course then you lose the savings you would have with SIPs that have wall board on the inside. Or would you screw the wallboard directly to the OSB? I find SIPs attractive for their insulating properties and the labor savings in construction, but wonder if they're best in the long term. I wonder how a structure framed with 2"x6" and sheathed with OSB, then coated with 1" or 2" of spray foam, (to seal the cracks), then insulated with fiberglass, covered with a vapor barrier and wall board would compare to a SIP structure in price and performance.

WTB;

EPS foam exposed to UV rays will deteriorate, but one of the reasons it's not good to send to landfills is its expected to last 300 years burried in the ground. EPS can be damaged by gasoline or solvents, but I wouldn't advise spashing any of that around wood framing either. The /OSB/EPS/Drywall is not structural as there in little structural value to drywall.

Long term: There are thousands of commercial refrigerated warehouses in use for decades using SIPs technology. Most of which are metal based and expected to last 300+ years.

RE: 2x6 ...... don't try to reinvent the wheel (or SIPs), fiberglass is old technology, EPS is safe and proven to be a superior permorming insulator

Some foam will be subject to "Off Gassing", which will cause the insulation value to deteriorate over time. If you do your research you will find several types of EPS that is not subject to "Off Gassing" and will maintain their thermal properties over time. Great question about needing to replace the sheeting on a SIP panel. I know that most SIP's rely on the sheeting, inside and out, for structural integrity; if you have a problem with the sheeting the whole panel may need to be replaced, that could cost a great deal of time if the panel is already in place. Like wise I don't think it is easy to change placement of electrical boxes outside of the channels provided, as soon as you start to make lateral cuts on a SIP panel you may be compromising the integrity of the panel. Our EPS is not subject to "Off Gassing" and will have the advantages of SIP panels that are attractive to you. It may be worth your time to view our website for a comparison.