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

[RT]

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

< A r c h i L o g i c  at  Y a h o o  dot  c a  >
(manually winnow the chaff from my edress if you hit "reply")