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Re: GSBN:Re: Moisture in SBW
- To: GSBN GSBN@...
- Subject: Re: GSBN:Re: Moisture in SBW
- From: John Swearingen johns@...
- Date: Mon, 25 Oct 2004 16:26:05 -0700
- Reply-to: "GSBN" GSBN@...
- Sender: "GSBN" GSBN@...
Hello Danny, et al...
I just wanted to throw in a few cents worth of comments on this subject
as I have been involved in a few houses with minor to major moisture
problems. Generally they have been as the Master of Moisture, John
Straube, described - related to poor design decisions and/or poor
detailing around windows, etc.
My basic design philosophy in general -
First principle - Design problems out of, not into buildings. In other
words think about what you're doing and what is going to happen over time
and how you can mitigate the bad things by design rather than through the
application of technology, high-tech materials, etc.
Second principle - Simplicity is its own reward. This makes carrying out
the first principle much easier...
Third principle - The roof should cover the tops of the walls...and then
some. This should be an absolute no-brainer for straw bale. Many of you
know my long-standing dislike of Santa Fe style architecture, but this
goes double for straw bale - parapet roofs, vigas sticking out of the
wall, roof drains penetrating the walls - all totally violate the first
Some of you may have heard me say this before, but for those who haven't
- a few years ago a woman asked during a presentation I was giving if it
wasn't true that straw bale buildings should only be built in dry places.
I said, after pausing to think about it, "Yes, that is true. But, you can
design and build dry places just about anywhere. Which is how I would
like you to think about what you're doing when you're designing a straw
So, Fourth principle - design dry places for your bales...
Okay, enough pontification...
The last thing I'll share is about windows and window sills. John aptly
pointed out that they leak - they always leak (unless you've been smart
enough to design them into really dry places). So protecting the bales
beneath the windows requires that you catch the water under the window
and make sure it gets all the way out of the wall. In other words,
ideally you would have a pan of sorts under the window, sloped slightly
to the outside, extending a bit beyond each side and with a lip at the
back and on each end (so water can't just run off the ends), and
extending out beyond the exterior wall surface, with a drip edge - so
that any water that leaks through or runs down the sides of the window
ends up in this pan and is shown the exit. You can make these pans out of
metal, plastic, ice and water shield, cast this shape into a concrete
sill, anything that will keep the water from leaking through it, but the
principle thing here is to make sure that the water can't get into the
wall below the window. You can put your window sill material, whatever it
is, on top of this pan flashing being careful not to punch unsealed holes
in it when you install the sill. It can take a little thought and
ingenuity to do this, but it assures you that when the windows leak the
water leaves the building.
That old practice of just putting roofing paper or plastic over the top
of the bales and setting your windows on it and then plastering over it
just leads the water down inside the plaster to the bales wherever the
water protection ends unless it runs continuously down the wall under the
window to below the bales (and we don't recommend doing that). It just
temporarily moved the problem down, didn't solve it.
That's all for now. Glad to see this discussion here.
David Eisenberg, Director
Development Center for Appropriate Technology
P.O. Box 27513, Tucson, AZ 85726-7513
(520) 624-6628 voice / (520) 798-3701 fax
<a target="_blank" href="http://www.dcat.net">http://www.dcat.net</a>
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I was going to comment on this issue, but David has said everything
there is to say, clearly and (imagine this!) succiently.