Is There Such a Thing as a Perfect Building Envelope?

The insulation method proposed by this GBA reader requires a lot of foam


Creating an air barrier at the sheathing level and insulating on the exterior with rigid foam insulation is key to the PERSIST and REMOTE building strategies as well as Andrew Homoly’s “perfect” building envelope.

Is there such a thing as a perfect building envelope? One that could be mass-produced from readily available materials, and be appropriate for 90% of all new homes?

Andrew Homoly thinks he’s found one, as he explains in this Q&A post at GreenBuildingAdvisor.

Here are the basic elements:

  • A conventional foundation insulated with 2 in. of rigid foam on the outside.
  • 2×6 walls sheathed with Zip System OSBwith 2 in. of rigid foam on the outside and open-cell spray polyurethane foam in the stud bays.
  • A roof sheathed with OSB, insulated on the exterior with 2 in. of rigid foam capped with another later of OSB sheathing over furring strips.
  • Soffit and fascia made from OSB sheathing, insulated on the exterior with 2 in. of rigid foam, and topped with furring strips and finish material.

It is this last detail, the insulated and vented soffit and fascia, that has Homoly thinking he’s nailed it. He calls his approach the Homoly-Pedley Perfect Envelope, sharing the credit with his framer, Mike Pedley, who came up with the soffit/fascia detai

“Note the ‘gap’ goes all the way up the wall, around the soffit, around the facia, and up the roof to the ridge vent,” Homoly writes. “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 … and could easily be mass-produced since it utilizes all common building techniques and materials.

Building Happiness

What is your goal in life?

After you answer, ask yourself “Why?”. After you answer this, keep asking why until you get to what you know is your final answer. For most people, it will go like this… “My biggest goal is to start my own company… or meet my future spouse… or start an exercise program…” When they answer the why question, it will sound like this… “So I can have more freedom… or to start a family… or to be healthier”. Continue reading