[greenbuild] Re: RASTRA: opinions, experiences?
- From: "STEVE PAISLEY" <pppaisley@xxxxxxx>
- To: <greenbuild@xxxxxxxxxxxxx>
- Date: Wed, 26 May 2004 15:36:42 -0400
Molly--
My aunt built a Rastra house in Seattle. Here's what I know/think about
it based on looking into it for her:
All the benefits you've mentioned seem to be true, and my aunt is pleased with
her house. The drawbacks seem to be:
Lots of high-embodied energy concrete and steel rebar needed.
Possible EMF distortions caused by the rebar grid--I don't know if there's
any real evidence of this having any effect on people or not, but some people
think it might.
The blocks are expensive, and rebar is not cheap either. If you're paying
someone to build it for you, you save on labor since it goes up fast and is
quick to finish if you use stucco/plaster. Total labor & materials for my
aunt's house came out about the same as for a stick-built house.
Hard to modify if changes or additions are wanted.
The effective R-values that Rastra publishes (including the thermal mass
benefits) seem to be a bit exaggerated based on an independent evaluation that
I read. Still, the performance of the wall was better that a standard
stick-built wall with fiberglass due to the elimination of air leakage through
the wall.
I believe there is a place in Freeville that carries Rastra. Scot (of
Frog Hill Pottery) said that he was planning to build something out of Rastra
soon. You might also consider Durisol blocks, which were used at the O/Nolan
duplex at ecovillage. They use wood chips instead of styrofoam, and I think
are made in Eastern Canada, as opposed to Rastra which has to come all the way
from the West Coast.
--Steve Paisley
----- Original Message -----
From: Molly Brewton
Sent: Wednesday, May 26, 2004 12:44 PM
To: greenbuild@xxxxxxxxxxxxx; NaturalBuilding@xxxxxxxxxxxxxxx;
permaculture@xxxxxxxxxxx
Subject: [greenbuild] RASTRA: opinions, experiences?
Dear Folks,
Does anyone have any opinions/experience building with Rastra? It sounds
really great. I've copied/excerpted some text below from various websites.
Molly
RASTRA is a concrete form system made of a lightweight material Thastyron
which provides a permanent formwork for a grid of reinforced concrete to
form load-bearing walls, shear walls, stem walls, lintels, retaining walls,
foundations, and other components of a building. 85% of its volume is
recycled material - postconsumer polystyrene waste.
Beneficial properities include:
No toxic outgassing; non-toxic or low-toxic additives.
breathes like a house made of natural materials
Makes thick, adobe-like walls. Can be easily molded or cut into desired
shapes. Easy to make curved walls.
Construction does not require high skill level (similar process to
strawbales).
Basement walls and Stem Walls can be built in less than half the time it
takes to form, reinforce, brace, pour, strip, and insulate a conventional
concrete block wall.
Does not require wood framing (wood is enormously expensive these days)
Very strong--superior wind, earthquake resistance; load capacity can be
adapted to any requirement.
strong pest resistance
mold-unfriendly
good soundproofing and acoustics
4 hour class A fire rating
good insulation value (I think, due to thick walls. It might need to be
lightly supplemented for Ithaca; not sure)
Can be quickly finished with a single coat of stucco - no mesh or lathing
is required.
OK with building codes; local examples of large buidings exist if needed.
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