Recommended exterior wall layout for North Carolina
I am investigating/interviewing contractors to build our new construction in central North Carolina, near Winston-Salem, where temperatures and conditions are milder than in the mountains. We are considering a hybrid timber frame with exterior SIP walls and roofing SIPs. Simply put, what would you recommend as the construction sequence and materials for the walls? We’ve been told that an R-22 wall system would be sufficient with a strong focus on preventing air leakage.
My question stems from having read so much on the subjects from a host of experts that I’ve ended up being confused. Finally, do SIP manufacturers simply build a stock wall or may ithey be open to constructing them based on a customer’s specifications?
Tom Gagnier
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Replies
Tom,
In your climate zone, an R-22 wall system installed with attention to preventing air leakage would be above average. Most building codes require only R-13 walls in your climate.
That said, there is no simple answer to your question. More insulation is always better, if you can afford the investment.
I'm not sure what you mean by a "stock wall." Most SIP manufacturers will build SIPs to almost any specifications, including custom home designs. They are usually delivered with window and door openings pre-cut in the factory. They are available in several thicknesses, so if you want a higher R-value, you can get it.
R-22 SIPs will insulate 2-3 times better than a 16" on center fiberglass batted "R-22" wall that has not been air sealed. And it better. SIPs are twice the cost in my area.
The seams are where the trouble lies. I would have the SIPs installed by a dedicated SIP factory team.
Tom - I have built a few homes near your area (Northern end of Iredell County in statesville) and we investigated just about every wall assembly we could come up with. SIPS are a great system and used a good bit in the mountains here but in my opinion are a little overkill and hard to justify the premium cost. We built a wood framed wall (2x6 @ 24" OC) with exterior foam (1" DOW SIS) blown in fiberglass/cellulose and paying close attention to air barrier and air sealing details - our overall R-Value was around R-28. These homes perform just as well as SIPS homes and were done for a fraction of the cost. Both homes had a HERS in the 50 range and have never had a utility bill more than $50 a month. I would consider pricing this option next to the SIPS so you can see what the premium will be and may make your decision easier.