[Strawbale] Alternative tightening materials

[RT]

On Sat, 05 Mar 2011 18:07:10 -0500, Sara Tommerup <stommerup at 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"