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Re: [Strawbale] Alternative tightening materials
On Sat, 05 Mar 2011 18:07:10 -0500, Sara Tommerup <stommerup@gmail...>
wrote:
Straw bale is obviously a brilliant choice to reduce the overall
embodied energy,
however, how do you go about the air tightening for a 0,6 ach/h value
in a straw bale house or frame with another low tec natural insulation
if you don't want to use foam, tape and membrane (etc)?
Sara;
Actually, blower-door tests on amateur-built strawbale houses here in
Atlantic Canada about a decade ago showed that the strawbale construction
methodology is inherently conducive to yielding air-tight buildings with
results that would in some cases, qualify them under the R-2000
performance standard, a standard that was developed for
low-energy/energy-efficient residential buildings in Canada in the early
1980's.
The process of wet-applied plaster eliminates the many joints between
panels that are created in "conventional" construction systems, those
joints being discontinuities in the air barrier that usually require the
use of acoustical caulking and/or gaskets in order to seal.
The houses that failed the blower door test usually only needed to have
penetrations in the ceilings (for electrical boxes or fixtures) sealed
before passing after re-testing with the blower door.
It's not all that difficult to avoid the use of foam, tape and membranes.
One just needs to identify all of the potential air-leakage points at the
design stage and then provide the details for a mechanical air-seal at
those points and then educate all of the people who will have a hand in
the construction, on their role in ensuring the integrity of the air
sealing strategy and then have someone who is competent, inspect the
construction at every stage to ensure that the strategy was carried out
properly.
You decide which is preferable (sealants, foams, tapes, membranes etc.) or
the latter.
As was intimated in the Canadian SBH example, penetrations for services
are major air-leakage culprits.
In the Olde Days, we would have to tediously design and construct
air-tight boxes into which electrical boxes would be placed but these days
one can simply purchase an inexpensive polyethylene pan that is
specifically made for the purpose.
A simpler solution would of course to to just not run any services in the
exterior walls.
Another major discontinuity is at junction between different
planes/surfaces and different materials.
These can be addressed with a flange that straddles the joint in a manner
that is similar to flashings for water shedding details.
--
=== * ===
Rob Tom
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"