[GSBN] Effective air barrier strategies (was re: Can bale buildings be air tight ?)

[Dusty]

Awsome, thanks RT!
I will pass the knowledge onward. Thanks for the reminder of things I have learned at one point and completely forgot!!!! There's just so much for us humans to learn (and re-learn)
Thanks for the publication links, and thanks to Canada for being so Cool!
Dusty

Straw & Timber Craftsmen INC
www.strawandtimber.com
dusty at strawandtimber.com



--- On Tue, 11/13/12, RT <archilogic at yahoo.ca> wrote:


From: RT <archilogic at yahoo.ca>
Subject: [GSBN] Effective air barrier strategies (was re: Can bale buildings be air tight ?)
To: GSBN at sustainablesources.com
Date: Tuesday, November 13, 2012, 11:26 AM


Competent and effective air barrier strategies for small residential buildings have been implemented for at least the past three and-a-half decades in super-insulated buildings here in Canada as a matter of course, simply because the horrible consequences of making air-leaky buildings became readily apparent very quickly and early on due to the nature of the climate.

Back in the previous millennium, Shawna Henderson did some blower door tests on a number of owner-built SBH in Nova Scotia under the auspices of CMHC back when Don Fugler was in there pulling for the SB community and confirmed what most of us already knew -- the potential air-leakage points in the homes were not specific to SB walls or SBH in particular.

They were the "usual suspects" -- penetrations in the interior air barrier for services and discontinuities at the junctions of dissimilar materials/planes/components that occur in building construction no matter what materials are used for the walls.  If anything, Shawna's blower door tests showed that SB walls were more amenable to effective air-sealing due to the wet-applied plaster process typically used in SBC and a couple met the performance required by the R-2000 performance standard of that time with a minimum of fuss.)

       http://oee.nrcan.gc.ca/residential/personal/new-homes/r-2000/standard/11018


As such, the air-sealing techniques developed over the years for "conventional" buildings is easily imported into SBC, often using the identical materials that are readily available at most building supply outlets. No need to re-invent the wheel.

So in reply to Dusty's query:

> I've been wondering if you have a technique for sealing the backside of electrical boxes ?

In the early days of super-insulated building construction, it was a a time-consuming process to  ensure air-tight seals at electrical boxes.

At one point some builders were making pans out of OSB or plywood screwed to a 2x3's and then lining the pan with polyethylene and sealing the schmozzle with acoustic caulking.

Eventually people acknowledged that OSB & plywood is air/vapour-impermeable and that air would have a difficult time moving through 1.5 inches of solid wood so the polyethylene liner was omitted and just the joints between the 2x3 lumber and OSB were caulked. Still, it was time consuming and messy to do.

And then about two and a half decades ago, poly pans for electrical boxes became readily available eliminating most of the futzing about that was associated with making electrical boxes air-tight.

Images of both of the above can be seen at  the following link:

   http://www.homebuildercanada.com/1606TT.htm

Another strategy from conventional SIBC that can easily be imported into SBC is to provide a chase for services inside of the plaster air barrier, eliminating penetrations altogether. I won't bother going into details here because this stuff is in the archives of any of the SB Lists and should be easily Googled.

And it's not good enough to simply lap one material onto another at a junction and call it "air-sealed".

If a mechanical seal cannot be made via geometry (ie fold locked seams or compression against a gasket ) then one usually has to resort to allowing for a bead of acoustic caulking (ie ensuring accessibility and concealment).

Details for air-sealing of specific areas and components are available for download, usually for free at the CMHC website in French and English. The drawings may depict conventional materials and systems but the techniques remain the same.

           http://cmhc.ca/

Also in the 1990's the Canadian Homebuilders Association published a manual that provided the same and would still be relevant today.  This one you'd have to pay for.

          http://www.buildermanual.com/




--=== * ===
Rob Tom                    AOD257
Kanata, Ontario, Canada

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