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GSBN:Re: Moisture problems

Oh dear - why do people build such HIGH RISK houses in the first place.

1) Do parapet walls "always" allow moisture penetration? Any experiences or
testing that might indicate why some did and others didn't?

Parapets run a very high risk of leaking in all types of buildings - if the
substrate is moisture sensitive then the risk is extremely high of severe
damage - why do it?  It seems really fundamental to me that the roof should
cover the tops of the walls Ð I would strongly recommend re-design.

2) Does 3-coat cement plaster (stucco) allow enough water to penetrate a
and substantially "soak" the bales? I seem to recall that Dr. Straube's
involved capillary uptake, but I don't think that if I had the rest results
front of me I would necessarily understand them without a really clear
explanation. How would this compare to rainfall on a vertical wall surface?

Cement stucco plaster runs a very high risk of leaking, and is not very
breathable either.

3) Will a sheet moisture barrier between the bales and the plaster cause the
bales to decompose?

Moisture barriers are a brave attempt to keep moisture out, but also work
very well at keeping it in, and some moisture may come from inside the
building and be trapped by the moisture barrier - breatheability of coatings
is of utmost importance Ð lime  plasters rather than cement based ones are
so good for this. 

4) Will a non permeable stucco function the same as a sheet moisture barrier
and cause the bales to decompose?


5) Is there any rule of thumb that would give us an indication that over
moisture content % the bales won't likely dry out, but under that % they
likely dry out. I understand that is a "difficult" question because much
depend on the drying conditions, but I was wondering if someone had reached
some conclusion made from personal observation in their experiences.

An interesting question - over around 18-20% moisture content fungal growth
will start - and mycelium can in some instances seek out moisture from some
distance away to keep the fungi alive - there was an instance in New Zealand
I am told by a building researcher here, of a timber building where the
fungal growth in the roof had sent down mycelium three stories to get ground
moisture to keep it alive!
If the bales should dry out the fungal spores are still in there waiting for
a chance to re-activate quickly so a second wetting will be much more
devastating than the first.

However, a direct answer to your question I do no know.

It all sounds to me like another case of a very high risk design that has
imperilled the reputation of straw building.

My 2c worth

Graeme North Architects,
49 Matthew Road,
RD1, Warkworth,
New Zealand 1241
Ph/fax +64 (0)9  4259305


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