PERSIST building method
I am reconsidering using OBS faced SIPs for wall/roof construction in climate zone 5A (Rochester, NY). The building design is 1500 sq. ft, frost-protected, slab-on-grade – monolithic pour. Shed roof, one floor plus loft.
I am interested in the PERSIST building envelope method but am having trouble locating construction method details.
For instance:
1: What is the best choice for exterior insulation? How is it attached to exterior sheathing? How is it laid out (pattern) and sealed?
2: What is best choice for exterior sheathing? Material? Thickness?
3: Are there special considerations for plumbing vents and other penetrations (ductless mini-splits, direct-vent gas space heaters?)
4: What is the best choice for the SBS membrane? Can the same product be used on the roof and wall sheathings?
Thanks
Dave
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Replies
Dave,
The classic PERSIST method doesn't use SIPs. For more information on PERSIST, see Getting Insulation Out of Your Walls and Ceilings.
Q. "What is the best choice for exterior insulation? How is it attached to exterior sheathing?"
A. Those questions, and many others, are answered here: How to Install Rigid Foam Sheathing.
Q. "What is best choice for exterior sheathing? Material? Thickness?"
A. That is a very basic question. If you are not sure of your sheathing material or thickness, you probably want to hire a builder, architect, designer, or engineer to help you.
Most homes these days are sheathed with OSB that is at least 7/16 inch thick. However, plywood holds up better to occasional moisture than OSB, and is preferred by many builders. If your local building department allows its use, diagonal board sheathing is an excellent choice.
Q. "Are there special considerations for plumbing vents and other penetrations (ductless mini-splits, direct-vent gas space heaters?)"
A. Any penetrations through your home's walls or roof need to be sealed against air leakage and water entry. This is done with flashings and sealants. It's a big topic, but there is plenty of information available on the GBA site if you use the "search" box.
Q. "What is the best choice for the SBS membrane? Can the same product be used on the roof and wall sheathings?"
A. SBS (Styrene Butadiene Styrene) is a type of roofing. You don't need to install SBS roofing on the sheathing of a PERSIST wall or roof. The classic material to use is a peel-and-stick rubberized asphalt membrane; the best-known brand is Grace Ice & Water Shield. If you choose this product, you can use it to cover the roof sheathing as well as the wall sheathing. The next layer to install on the exterior side of the rubberized asphalt is the rigid foam.
It's also possible to use a liquid-applied WRB if your prefer, although the product isn't usually used for roofs.
Thanks Martin....I understand PERSIST doesn't use SIPS. I initially learned about PERSIST through the article you mentioned! I think Joe L's article, The Perfect Wall comes very close to describing the PERSST method.I am really glad I found that article as I had almost fully committed to SIPS. Indeed, I am working with a licensed architecht and will be getting qualified assistance from local builders.
In the PERSIST method, the building envelope requires no eaves or overhangs, so vapor/water/air shield is simplified. I get that. My current building design (shed roof) calls for overhangs all around. I have read that I will need to construct the overhangs separately, apply the peel and stick, then attach the overhangs. Any thoughts there?
Thank, as always.
Dave
Dave,
Q. "I have read that I will need to ... apply the peel and stick, then attach the overhangs. Any thoughts there?"
A. My article, Getting Insulation Out of Your Walls and Ceilings, includes two detail drawings showing applied overhangs (soffits) designed to be installed after air sealing the crack between the wall sheathing and the roof sheathing.