[permaculture] Question about Earth Homes, thermal mass and humidity

katey culver 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
teachers :-)).


Katey Culver

“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.”
~Joanna Macy

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)
> average
> 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
> fronts,
> 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
> of
> examples--I'm not referring to isolated cases. Strawbale and earth
> buildings
> 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
> colonise
> straw wall interiors) before commencing to lay any earth or straw wall
> materials, as an insurance against flash-flooding (bathrooms are required
> to
> 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
> moderation.
> Ciao
> Robyn

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