[permaculture] Question about Earth Homes, thermal mass and humidity
newtribe at hughes.net
Fri Feb 5 19:29:42 EST 2010
Very interesting stuff, Robyn. And what serious conditions! I wouldn't
call the weather comparable to the Southeast US. Unless we're talking
about southern Florida and i have no experience there.
So traditionally the houses are sided with wood? We don't do load-bearing
straw bale. We, too, use timberframing for the structure with straw
infill. Hope Penny's plaster recipe helps (she was one of my permaculture
“The most remarkable feature of this historical moment on Earth is not that
we are on the way to destroying the world-we've actually been on the way for
quite a while. It is that we are beginning to wake up, as from a
millennia-long sleep, to a whole new relationship to our world, to ourselves
and each other.”
On Thu, Feb 4, 2010 at 1:07 AM, Robyn Francis <erda at nor.com.au> wrote:
> Hi Katey
> You asked about my experience...
> I'm an owner-builder several times over and been involved in following,
> observing, researching and teaching natural building, solar design and
> bioclimatic building for over 30 years. I collaborate with a number of
> builders and architects with long experience in this and other climates. In
> our subtropical climate we receive around 70-75 inches (1750-1850mm)
> rainfall during the summer/autumn wet season, with extreme humidity and
> storms delivering 4+ inches in an hour driven horizontally by strong winds.
> Much of this occurs as monsoonal and cyclonic rains. In between rain
> temperature and humidity levels soar. Winter and spring are dry with huge
> temperature extremes, over 30degC difference between max/min in a 24 hour
> period, hence a lot of condensation on hard surfaces.
> My observations are based on the performance of natural buildings in this
> climate since the '70s. This part of Australia is a hot-spot for
> experimental and natural building for the past 30+ years, so there's lots
> examples--I'm not referring to isolated cases. Strawbale and earth
> have a sad track record here, even with excellent damp coursing. The
> building code requires a 1.5m (5 ft) overhang for earth walls, but this has
> proved inadequate for severe weather events.
> It's is also usual to lay several courses of fired bricks or stone wall on
> top of the foundations (i.e. above floor level) with a second damp-course
> and termi-mesh (prevents termites but not the small black ants that
> straw wall interiors) before commencing to lay any earth or straw wall
> materials, as an insurance against flash-flooding (bathrooms are required
> have floor drains as a matter of course) and rising damp.
> Our valley soils are highly plastic, reactive clays, not well suited to
> earth construction, or supporting heavy wall structures. Even with
> over-sized foundations, the movement of soil (expansion/contraction) from
> the extremes of wet and dry seasons, inevitably results in cracks in
> plasters on strawbale and cracking in earth wall structures (cob,
> earthbrick, rammed earth, also cement and regular fired/cement brick walls
> as well). I agree that strawbale with a timber frame has inherent degree of
> flexibility in response to foundation movement, but thick plasters don't
> have the elasticity to cope with much movement without cracking. Once the
> integrity of the render is compromised, moisture can enter...
> Most traditional houses here are timber on stilts with big verandas and
> corrugated iron rooves. This is ancient volcanic humid subtropical
> rainforest country. Local hardwood timber in this climate has continued to
> hold its own as an exceptionally appropriate and durable natural building
> material. The saw-ment in timber frame also works and lasts very well.
> BTW I'm currently building a studio with corrugated roofing iron external
> wall cladding and will experiment internally with bamboo wattle daub, cob,
> mud-straw and other earth wall techniques for insulation and thermal
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