Replies

1. GBA Editor
   Martin Holladay | Oct 22, 2018 09:50am | #1

   User-7203597,
   First of all, can you tell us your name? (I'm Martin.)

   Q. "Which is better?"

   A. SIP construction is faster but more expensive than conventional construction methods. It is not "better."

   In cold climates, SIP roofs can fail catastrophically due to rot caused by the moisture associated with exfiltratring air. To prevent this type of catastrophic failure, pay meticulous attention to air sealing details at SIP seams.

2. 
   JohnPaulJames | Oct 22, 2018 11:53am | #2

   Sorry about that, my first post.... my name is John

   Sounds like conventional construction might be a better route to go?

   The floor plan is about designed, allowing for conversations with potential contractors. I expect that most are going to be traditional method builders in rural MO.

   From all I've been reading, exterior foam insulation is the better method. Zone 5 calls for R-30 walls. Anybody have experience[s] in convincing 'old contractors new tricks'? How alien will it be if they've never done exterior insulation before? I may be just anticipating a problem that doesn't exist. Won't know until I start looking.

   Thanks

3. 
   AlexPoi | Oct 22, 2018 01:34pm | #3

   Exterior foam is much better than sip panels in my opinion. In both cases, you rely on the foam to act as your air barrier (unless you put a membrane under the foam).

   With foam panels, you can have two layers of panels, overlap them and tape them to ensure a pretty good seal (bear in mind that foam can shrink, so it's important to use a good tape that won't tear out because of that shrinkage). You can't do that with SIP panels. Instead, you must seal all the seam with a special sealant and you must be very meticulous about it. Otherwise, you'll have condensation problems. It's take time to do a good job and it's not as robust as overlapping foam boards on top of your sheating.

4. Expert Member
   Peter Engle | Oct 22, 2018 02:53pm | #4

   Success with SIPs requires attention to detail, and that may be difficult if the contractor does not have experience with them. Also, distance to a SIP manufacturer is an important cost and schedule consideration. You can get standard lumber anywhere.

5. GBA Editor
   Martin Holladay | Oct 23, 2018 05:29am | #5

   John,
   If you are just beginning to think about wall design, you probably want to read this article: "How to Design a Wall."

1. 
   JohnPaulJames | Oct 23, 2018 06:00am | #6

   Thanks!

   John

2. 
   JohnPaulJames | Oct 23, 2018 01:05pm | #8

   Wow Martin,

   Read the recommended article... which lead to another and another.... :-)

   Lots of great info out there.

   In one of the articles [maybe more than one] it is stated that either exterior foam or Double Studs is acceptable. Also seem to remember that double stud was cited as being less expensive and more likely to be accepted by traditional builders.

   Is my simplistic summary accurate?

   Is there any reason to choose exterior foam over double wall construction?

   Thanks

6. 
   brp_nh | Oct 23, 2018 08:26am | #7

   John,

   I'm not a builder or building expert, just a homeowner that was very involved in designing and building our energy efficient home in zone 6. Before you decide on a wall design, I'd suggest a couple things:

   Plans/Design - I'd run your house design, floor plan, and siting by someone knowledgeable with energy efficient home design. It's possible/likely there could be improvements with the design/siting that would have a major effect on energy efficiency.

   Builder - It's hard to find a good builder and even harder to find a good builder with experience building high performance homes. If you can't find the latter because of your location or budget, I'd focus on finding a good general builder and work with them on incorporating energy efficient features in the wall design, HVAC, etc. At least look into a builder that is involved with the Energy Star program.

   My impression from reading GBA for many years is that while exterior foam is a preferred wall design, many homeowners have a hard time finding a builder with that experience or a builder that can do it at a competitive rate. I'd absolutely keep that wall design on the table, but I'd also add in a double stud wall because the outer wall specs are going to be similar to a standard 2x6 wall.

   Brian

7. GBA Editor
   Martin Holladay | Oct 23, 2018 02:00pm | #9

   John,
   Q. "Is there any reason to choose exterior foam over double wall construction?"

   A. A properly designed wall with exterior rigid foam will have exterior sheathing that stays dryer that the sheathing in a double-stud wall. That's an advantage -- although not necessarily enough of an advantage to tip the scales. Keep reading, and be prepared to make your own decisions.