Homoly – Pedley Perfect Envelope?
I was just asked again today… “What is the best way to build the envelope of a home?” I know the real answer is “it depends” and then we could launch into the hundreds of different techniques. I feel the green building community, however, needs to provide an answer that applies to 90% of all homes. This shouldn’t be that hard as 90% of all homes are built the same way now…stud walls, OSB sheathing, house wrap, some kind of siding, and batt/blown insulation.
I have a proposal I would like to run by my fellow green thinkers that basically just puts a lot of great existing ideas together in one package (most notably the Joe Lstiburek Perfect Wall/Roof concept). I am building this home right now as a test case. Here are the details…
Foundation: Traditional poured foundation (or whatever is most common in your area) with 2 inches rigid foam on the outside and termite shield at the top.
Walls: 2×6 walls, OSB (I’m even using Zip Wall for a belt and suspenders approach), 2″ rigid foam (the key here is to use 40psi foam to keep the foam from “sucking in” different amounts to give the siding a wavy look – this is a standard stock item), house wrap, firing strips, and then the siding (we are using Hardie). Open cell foam between the studs (although there are other options here – I like open cell to allow the wall to dry out to the inside WHEN water gets in).
Roof: OSB sheathing (again, I am using the Zip System for belt and suspenders), 2″ rigid foam (this foam can be the traditional 25 psi because the foam won’t squish unevenly as badly when an entire 4×8 sheet is being screwed down), firring strips, OSB sheathing, roofing underlayment, shingles with a ridge vent at the top.
Here is the big new idea that makes it an “envelope”. My framer Mike Pedley came up with this detail, so hence his name at the top.
Soffit and Facia: OSB sheathing, 2″ rigid foam, firring strips, soffit and facia material.
Note the “gap” goes all the way up the wall, around the soffit, around the facia, and up the roof to the ridge vent. Periodic vent strips could also be added in the soffit if desired. The entire home from foundation to wall to soffit to facia to roof is wrapped in an uninterrupted thermal envelope.
I believe this system accomplishes multiple goals (as outlined in detail throughout this website) and could be easily be mass produced since it utilizes all common building techniques and materials.
What do you think?