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Re: GSBN:Loadbearing sb with moisture damage



Laura, Chris and all,

The issue of good moisture detailing for windows is, in my view, one of
the most important and most often neglected aspects of sb design and
construction. When you talk with the people who look at moisture
failures in buildings for a living, this is often cited as the most
common or one of the most common areas of moisture damage and failure.

 It is a more important issue to get right in bale walls because they
are susceptible to moisture damage. That it is so often a problem in
conventional construction should not make us less vigilant or diligent.
And this is important - good design and detailing should never rely on
caulking as the only method of preventing moisture from getting into
the walls around windows.

Here is my ideal scenario - what I would like people thinking about as
they design their detailing for openings in bale structures. There
should be flashing all around the opening that is, in essence
"shingled" - overlapped starting from the bottom, so that any leaks are
directed onto (not behind) the next piece of flashing, and eventually,
out of the wall. There are a number of products available with which to
do this and this is one place where I think the judicious use of
synthetic materials makes a great deal of sense. This flashing should
not just be applied over the surface of the plaster, but should start,
ideally, behind it so that the plaster is actually part of the
shingling system.

I'm a big proponent of having a sill pan (which can be made of hard or
soft waterproof material - could be the same material as the rest of
the flashing), which extends underneath the window and a bit beyond
each side of it, is turned up at the back and sides (so that water
can't run off the back or ends into the wall), preferably slopes to the
outside, extends beyond the exterior finish surface, and has a drip
edge.

The less weather exposed the window, the less critical this detailing
is. But if the wall above the window is going to see rain, ideally we
would have a piece of flashing that extends above the top of the buck
and up behind the plaster. I know this is a challenge, especially if
you are cutting an opening into the wall after plastering. But if the
top of the buck had even a small strip of wood nailed to the top and
set back so that it was behind the inside surface of the exterior
plaster, the flashing could be attached to the top of this strip and
extend out and down the face of the top of the buck. It should be long
enough to be able to  overlap over the top of the window as well as the
top of the side flashing. Then, moisture that got to the inside face of
the stucco above the window, and moisture that leaked behind the trim
at the top of the window would not be able to end up inside the wall or
sitting on top of the window buck or the top of the window.

It is important to note that caulking, even the best caulking, is only
going to reliably last a few years. If it is all that you are depending
on to keep moisture out, and it is hidden by trim or in places you
rarely or ever inspect and maintain, you have designed in a problem
rather than designing it out. It's much easier to think these things
through before you build and if it's too hard to visualize this, build
a mock-up, a model, of what you're thinking about building and work out
the details at full scale where you can try different things and even
test them...

When I was building, I used to try to think like water - how could I
get in and how could I get out. Use great care in your efforts to keep
water out, and, knowing that you will not be able to achieve this
completely, take as great an amount of care making sure that the water
that does get in can get out. Of course I also used to think that you
"only had to be smarter than water" to do this and it turns out that
like many others, I had woefully underestimated the IQ of water...and
similarly overestimated my own...

What  I love about this forum is that we are, as a group, so interested
in learning from our own and others mistakes and discoveries and
sharing that learning openly.

David Eisenberg

-----Original Message-----
From: Laura Bartels laura@...
To: GSBN GSBN@...
Sent: Tue, 07 Mar 2006 20:50:30 -0700
Subject: Re: GSBN:Loadbearing sb with moisture damage

 Regarding cutting out windows after basecoat (or all coats) of
plaster,
 I have always scratched my head over doing good moisture detailing
after
the window does go in. Any comments?
Laura

Chris Magwood wrote:

> From our point of view, it took about the same amount of time to
> frame everything up first and then stack and plaster compared to
> stacking and plastering and cutting out later. The reason we didn't
> keep doing it this way? Well, what do you do with a bunch of 3x5
> foot, 21-inch thick hunks of bale wall that weigh hundreds of pounds
> each?
>
> Chris
>
>
>
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