I know, not the most exciting subject - probably only interesting to people building an energy efficient house. But hey, a lot of thought went into this one.
Most US houses are built with stick framing - think 2X4's with fiberglass insulation between. Research indicated that the insulation value is about R9. It also suffers from not being the most solid construction relative to other methods.
Another option was an enhanced stick framing - basically make the walls thicker (like 12 inches) and then throw in a bunch more insulation. It's the cheapest way to make an insulated wall, but we weren't fans.
Since we were already doing a timber frame house - a structural insulated panel (SIP) seemed to be the most logical option. It's basically some type of rigid foam insulation sandwiched between two pressed particle boards of OSB. You basically have two choices in the insulation material - EPS (think cheap styrofoam cooler you buy in the grocery store) and polyurethane (think the yellow insulation you find in your refrigerator. The latter allows for higher insulation values with the same thickness. The other advantage with the company we went with (Thermocore) was that they'll take you building plans, have their computer cut the panels precisely (including window openings), and also run the electrical conduits on the exterior walls at no additional cost.
The guys at Thermocore love their 4" product, since that is the standard wall thickness and makes installing doors and windows easier. But we went with the thicker walls - 6.5" - it was only a little more cash and the r-value was 40 - (I'll skip the debate I had with my HVAC guy on the degradation of polyiso over its lifetime)
A note on cost ... with the budget and design pretty much set, I can now speak with some authority on the topic of whether SIPs (specifically polyurethane) is more expensive than stick framing. If I'm comparing the simple cost of materials - then stick framing is cheaper - no doubt. SIPs cost us $46K, whereas we'd probably get by with $28K on materials for exterior framing - $18K difference. SIP labor is probably half at $5K vs $10K because the SIP factory has done all the cutting and the structure goes up in a week - the difference is now down to $13K. The walls are R40 instead of R9, and the house is much tighter, which means you save on the size of a traditional HVAC system - we didn't go traditional HVAC, but I'd guess we'd save about $5K with a smaller HVAC system - so we're down to $8K difference. So for a 2400 sqft house, I'm paying an extra $3/sqft for R40 walls as opposed to R9 - depending on heating and cooling costs in your area, you can get that money back pretty quickly. So if you're planning on building a house that is going to be around longer than you are - I'd say it's worth it.
At the very least when you're at this stage of building a house, and you hear the "Oh, SIPs cost more than traditional framing" - make sure you ask them "How much?" and "Do I save in other places in the house that help make up for the premium?"
