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Re: GBlist: Re: Housing Costs



We have done a number of variations on the complete conc. wall - the
basic is a simple cast in place conc. wall with an eps core:
The biggest problem is getting some structural integrity between the two
conc. layers without creating any thermal bridging. Generally we have
designated one of the layers as structural and the other cosmetic or
have used thin concrete panels as non structural (except lateral) and
have thickened a post or buttress section as the supporting member.

Use of concrete can be substantially more expensive in areas such as
ours as buildings need to withstand movement of 6.2 and so have to be
quite stiff. In all cases the eps layer is a continuous wrap around the
building. This has been quite important as the foam acts as building
wrap as the potential for moisture diffusion through the concrete is
quite high. 

I think the system is excellent but if quality results (smooth
consistent walls)are a concern the process is best left to controlled
pre manufacture and there are some companies doing this. We have
attempted highly finished walls and the results are good but involve a
lot of traditional handwork (concrete wall bagging is a lost skill) Less
work than a full stucco or plaster finish but finding the expertise is
difficult. I have liked to work with some of the material limitations (I
like the look of concrete) especially in contrast with other more
finished materials.

I initially worked with concrete wanting to increase mass and produce
walls that required little maintenance. I'm now not sure if the
substantially increased interior mass is really effective in our region
in heating applications but its cooling effect is quite good here. I
have noticed modifications of exterior climate (micro climatic effects)
and this is something I am looking at more.

Concrete does have a high embodied energy content but if designed well
(not wasted) in thin sections as a skin and using it to support loads
only where required it would probably compare well with most systems.
The lime content in concrete inhibits biological growth and the material
itself 'should' be relatively inert but depending on where it is
manufactured it could contain a % of toxic waste (ash from the
incineration of garbage etc. used in the manufacture). Radon is a
concern especially from aggregate used however there is 'new discussion'
on the potential beneficial effects of low level radiation - god knows
where that discussion will end up.

We have incorporated the slip form rock wall - double with an eps core
(similarly described by Tim, below) in all our projects so far.
Generally we used it as a skirting or short wall or pier but have also
gone to 18' heights as columns between conc. walls.  I have found it
most cost effective at a 2' approx.  level (using slip forms to get more
height and having to move rock and pour conc. at greater heights gets a
lot more labour intensive). We've used river rock as it is a regional
material and can be delivered to site (oversize rock is used in road
construction) it also stacks well and therefore incorporates some of the
traditional structural and aesthetic aspects of a stacked wall. Rock in
concrete walls are more prone to climatic effects especially moisture
and freeze/thaw conditions that can break or loosen rocks however I have
found that rock in concrete seems to perform better than rock in
traditional mortar mixes, in other words I haven't had any loose rocks.
Moisture can be a problem diffusing through the concrete and collecting
against the eps layer, more so than a straight concrete mix so if you
are concerned about the integrity of the weather barrier a waterproof
mix or a crystallization agent should be used. Radon is a concern (or
not a concern).

Another method that I quite liked involved pouring smaller wall sections
flat. We used a coloured sand/sawdust cement mix (stucco mix
essentially) poured to a 3/4" thickness over eps foam (in a form) The
material was screeded, floated and lightly broomed. The finish was
similar to a traditional japanese earth wall. The panels were quite
light and set into a curtainwall frame. Any kind of natural or unnatural
fibre can be used to prevent cracking or the panel can incorporate some
kind of mesh or lathing.

All of these techniques were used in houses that cost no more in final
construction costs than a regionally comparable tract house.
Affordability has been a prime motivation. In all cases we attempted to
produce a level of finish that would be attractive to someone not
predisposed to or inspired by 'being different',acceptability has also
been a motivation.  A larger percentage of the cost of these homes has
remained in the community as a higher percentage of cost is labour,
community economic development is also a concern. 

I have to mention that the end cost of these projects was more a result
of the overall planning and detailing than of any particular system
used. I've generally started with a budget and developed the most
appropriate system or set of technologies based on environmental and
regional concerns within that budget. The design process included
developing techniques that could be reproduced by people with few
related skills. The end cost has generally not included the research
involved in that design process and I'm sure many on this list share
that experience. The problem with this kind of approach is that after
researching one or another process the tendency is to become a little
over enthused about the particular merits of a technology you spent far
too much time checking out. In a community design process this aspect
can be particularly grating as there is little consensus and far too
much irrelevant technical discussion.

A useful community or perhaps internet tool would be an association of
relevant practitioners that could develop an appropriate methodology for
a specific project.

John


Barkeater Design Co. wrote:
> 
> Buzz wrote:
> >
> > * Concrete.  My personal idle thought:  figure out a complete wall
> system
> 
> > that integrates structure, insulation, and aesthetic finish with a
> cost
> > effective method.
> 
> We are having pretty good success with our double wythe slipformed
> stone
> wall.  Two slipformed stone walls encase a scrap stress skin panel.
> We
> are
> now getting each wall (wyth)lean enough to have to depend on the other
> for
> strength.  The technique is quite fast.  check us out at
> http://www.slic.com/~barkeatr/.  Slipformed stone seems to be left out
> of
> teh talk a lot, the only downside is the embodied energy of the
> concrete.
> We feel this is justified in the fact that the stones take up a lot of
> the
> wall, and we are using a frost protected foundation ie, saving 4 feet
> of
> conc frostwall. Also this wall will outlast many other alternatives.
> Key
> in this system is that a chunk of wall can (and did!)sit out during
> the
> winter allowing all sorts of financial (and other freedoms).  I  think
> this
> would be a great way to get strawbales off the ground and dry.  Anyone
> stop
> in and take a look!
> TIm McCarthy
> barkeater design build co.
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