High Performance Double Wall Construction


Wheatland Passive House is well on its way both under construction and though the certification process. We are in line to meet all of the PHI requirements. I figured it was a good time to go into some details on our 4th go around at double wall construction, and what we have learned in the process.

I have dealt with double wall construction on previous projects, but I it was well before my Passive House training.

While I was with Airtight Services we did a wide range of consulting and along with insulation services, but cellulose is the specialty. They can dry blow, dense pack, and damp spray cellulose. The preferred method for us insulating the double wall system is to install a fabric on the back side of the interior wall and insulate the outer wall and empty cavity with dry blown dense packed cellulose. Samples can be cored and weighed to ensure correct density. Once all of the rough in mechanicals are in, the remaining interior wall can be damp sprayed (and any interior walls can be damp sprayed for sound deadening) to complete the insulation package. This is ideal because it maintains a protected air barrier with few penetrations allowing drying potential in either direction depending on interior and exterior finishes.

“Original Double Wall — July 2010“

This project didn’t start off as planned.

As you can see, there are a few problems right off the bat:

  1. No fabric was installed between the walls for us to dry blow the cellulose. The wall is too thick to install damp spray cellulose in the entire wall — It would NEVER dry.
  2. There were also quite a few areas where plumbing was running between walls. So we’d have to work the fabric around the obstacles.
  3. The studs were lined up, so you couldn’t physically get a stapler between them to staple up a netting after the fact.

We were forced to work the netting in between the walls in small sections. There were some areas (above and below windows) that were too small to work in, so we had to face staple the netting.

This was the common wall between the house and the garage — it came out pretty nice…
But this is what most of it looked like

It was tight enough for us to insulate the wall though

It worked out okay because we were actually pushing the netting against the framing, so we didn’t need to bunch of staples — except on the ends.

We learned a lot on this project — what to do, what not to do. A few years later we were fortunate enough to go to the Passive House Tradesmen course in NYC

Airtight Services Gang 2014
After learning some great new techniques, some material science, and terms like “Floppy Bit” we were ready to try the double wall again.

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Matthew Bowers
Matthew Bowers
Matthew Bowers spent 6 years in the Navy as a nuclear engineer and became interested in Thermodynamics and Fluid Mechanics. Once his tour…

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