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FW: GSBN:Exterior cladding question



-----Original Message-----
From: Strawbalefutures [<a  target="_blank" href="mailto:info@strawbalefutures.org.uk";>mailto:info@...]
Sent: 07 February 2005 07:43
To: GSBN
Subject: RE: GSBN:Exterior cladding question

Hi Chris
I can't give any scientific proof though I know there are others who will,
but my instinct is that air gaps behind bale walls are not a good idea. They
are most often designed to provide a ventilated space when the cladding is
not regarded as breathable enough to keep the straw healthy. In practice
they are really difficult to achieve unless you put in an awful lot of
meticulous time that is not cost-effective unless you are a self-builder.
It's very much like the 20th century cavity wall idea that sounds like it
might work in theory but which has proved to be a very bad idea in
practice - it's hard to actually build it so it works!
If it was my design, I'd do what you propose and push the bales up tight to
the clay block wall. We're used to using straw embedded in clay without it
suffering, and we have many fine examples of wattle and daub walls stuffed
in the middle with straw from many centuries ago. And there is breathability
in the clay. It's just not the sort of material to allow moisture to
condense on its surface as it passes from inside to outside, I can't imagine
that happening.
As long as the compressed blocks don't contain any additives that would make
them behave unnaturally, I'd do it. It will be an interesting one for us all
to look at and assess next year. And it might encourage others to use more
compressed blocks too!
Let us know what you decide.
Best wishes
Barbara

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-----Original Message-----
From: GSBN [<a  target="_blank" href="mailto:GSBN@...]On";>mailto:GSBN@...]On</a> Behalf Of Chris Magwood
Sent: 07 February 2005 03:38
To: GSBN
Subject: GSBN:Exterior cladding question

Hello all,

I'm in the midst of designing a building for the Town of Haliburton,
Ontario, which will provide a new space for a charitable group in which
they will run their food bank and thrift store operations. It's a great
project, as the building has an honourable end use and will be located
right in the centre of the town, next to the art gallery and a park.
They are also keen to make it as sustainable as possible.

One of the requests of the town council is that the building be
designed to "fit in" with the existing local architecture. The art
gallery used to be a train station, so it's a nice building to echo.
But part of fitting in in this part of Ontario is a having a brick
finish. I've done some brick and stone facades in front of bale walls
before, but I'd rather not do them again.

One option I'm looking at is the use of compressed earth bricks. I had
a chance to see them being produced and even to lay some up during the
ISBBC in Denmark this summer. A local builder has recently purchased
one of these machines, and I've already decided to use them in the
floor.

I don't have any doubt that the earth bricks can be used as an exterior
cladding. What I'm wondering is this: If I lay up the bricks as an
exterior load-bearing wall, can I stack the bales directly against this
wall? I'm a convert of the Tom Rijven school of dipping bales in clay
slip, so I would dip the back side of the bale and press it against the
earth bricks, then give the interior the usual coat of earth plaster.

The issue is permeability. Obviously, the compressed earth bricks are
going to be less permeable than the plaster, based on the thickness (10
inches) and the density. But do you think this will be problematic?
Will the earth bricks be capable of taking up migrating moisture and
letting it go to the outside at a reasonable rate? I'm pretty good at
detailing a bale building by now, so there won't be any gross air
leakage, just what makes it through the plaster. I would treat the
earth bricks with silicate paint, which shouldn't hamper the
transpiring of moisture much.

I don't really want to do a typical brick veneer with an air space
between the bales and the bricks. Having done it before, I know that
it's nigh on impossible to maintain an even air space with a bale wall
unless you get into using wooden spacers or other material and time
intensive fixes. It seems to me that a patchwork of air gaps surrounded
by bales contacting the bricks would be worse than no air space at all.
So my option is use the bricks, or don't use any cladding and just make
the exterior plaster nice and square.

Let me know what you think...

Chris

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