kimchi & kraut

Passive House + Zero Net Energy + Permaculture Yard

Wall Assembly

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Or: Dude, what’s in your walls?

When choosing what to put in our walls, we knew we wanted to try and balance high R-values (well above the current building code) with a limited environmental impact.

Here are three articles that address the issue:

(choices)

(no foam)

(twinkies)

After evaluating various materials, including sheep wool,

goodshepherdwool.com

blackmountaininsulationusa.com

we decided to use many of the following elements employed by Hammer & Hand:

madrona-wall-assembly-914x1024-e1459377577722

Hammer & Hand wall assembly for their Madrona House.

In terms of materials, there are any number of options for putting a wall assembly together. For instance, we really wanted to use the sheep wool, but cost and worries (unfounded or not) about availability, led us eventually to Roxul (the Hammer & Hand videos below proved especially helpful in this regard).

After seeing the wall assemblies Hammer & Hand has been using, and how they’ve evolved over time, we felt the Madrona House set-up represented a good balance between cost-environmental impact-availability-ease of installation. We will also be following their lead by using the Prosoco R-Guard series of products to help with air-sealing our building envelope.

Nevertheless, we did make a couple of changes to the Madrona House set-up. For example, we’re using 4″ of Roxul Comfortboard 80 on the exterior side of the Zip sheathing (based on our colder climate zone), and we will be using Roxul R23 batts in the stud bays, along with the Intello vapor retarder, stapled and taped to cover the stud bays. Otherwise, we will be sticking pretty close to the Hammer & Hand Madrona House wall assembly.

So from drywall to exterior siding (interior – exterior), this will be our wall assembly:

  • 5/8″ Drywall
  • Intello Plus vapor retarder (475 High Performance Building Supply)
  • Roxul R23 Batts in 2×6 stud bays (24″ o.c.) (roxul.com)
  • Zip board (for structural sheathing and WRB; seams covered w/ Joint and Seam Filler)
  • 4″ of Roxul Comfortboard 80 (two layers: 2″ + 2″)
  • 2-Layers of 1×4 furring strips (aka battens or strapping) as a nailing base for the cedar siding
  • 1×6 T&G Cedar (charred and oiled with a few boards left natural as an accent — most of it oriented vertically, hence the need for a second layer of furring strips).
wall-assembly-color-coded

A crude rendering of our wall assembly using my daughter’s colored pencils.

A collection of helpful videos explaining the various elements we’re going to use, and why they’re effective:

Without the information available from sources like Building Science Corporation (they have a lot of interesting research documents) and design-builders like Hammer & Hand (not to mention Green Building Advisor and similar sites and forums that allow consumers to Q&A with expert builders and designers in “green” architecture), trying to build structures to such exacting standards (e.g. Passive House – Pretty Good House – Net Zero) would be exceedingly difficult, if not impossible, for those without previous, direct experience in this type of building program. I can’t express how thankful I am that so many individuals and businesses like these are willing to share their years of experience and knowledge with newbies like myself.

Here are the Hammer & Hand videos that initially sparked my interest in using Roxul rather than foam:

Instead of using tape for exterior seams, we are going to use the R-Guard series of products from Prosoco:

For various interior seams and connections we anticipate using the Tescon Vana tape, or an appropriate gunned sealant.

Helpful Links

GBA (Green Building Advisor): Building Green (Starter Q&A)

GBA: Article on minimum thickness of exterior foam by climate zone

GBA Question: Foam vs. Roxul

GBA: 10 Rules of Roof Design

GBA: “Greenest”

GBA: Passive House Design (5-part video series) Requires membership after Part I, but well worth it.

BSC (Building Science Corporation): Perfect Wall (pdf)

BSC: Hygrothermal Analysis of Exterior Rockwool Insulation (pdf)

BSC: Moisture Management for High R-Value Walls (pdf)

BSC: Cladding Attachment Over Thick Exterior Insulating Sheathing (pdf)

GBA: Mineral Wool Over Exterior Sheathing

Passivhaus Trust (UK): how-to-build-a-passivhaus-rules-of-thumb (pdf)

GBA: The Pretty Good House

GBA: Passive House Certification: Looking Under the Hood

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