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Re: GSBN:Fwd: CASBA_ Pea Gravel

Hi David & Anni,
I agree with you. If there is water in the bales to the point that drainage
at the bottom is required, I would recommend their removal. For 5 years we
have been using a 90mm deep bottom boxing with the cavity filled with Bulk
insulation to avoid a thermal bridge. The top of the bottom boxing is then
covered with structural ply.
The main reason that we have the 90 mm (4") bottom boxing is in the case of
an internal spill such as a washing machine or bath overflow. We use a 19mm
polyester strap with 1,100 kg breaking strain to compress the bales. This
strapping is fitted under the bottom boxing, so the bottom boxing also helps
with compression.

In the instance of a washing machine overflow, I doubt that 1" of gravel
would be sufficient to  prevent the water traveling into the bottom of the


Brian Hodge
Anvil Straw
----- Original Message -----
From: "Catherine Wanek" cat@...
To: GSBN@...
Sent: Wednesday, December 12, 2007 2:18 PM
Subject: GSBN:Fwd: CASBA_ Pea Gravel

I am forwarding this inquiry from the California
Straw Building Association (CASBA) list from
award-winning architects David Arkin & Anni
Tilt.   Perhaps this will stimulate discussion on the GSBN e-waves.

From: "David Arkin, AIA" david@...
Date: Tue, 11 Dec 2007 17:21:39 -0800
Subject: CASBA_Mem Pea Gravel
Fellow CASBAnauts (CASBAnuts?):

We haven't used pea gravel between our sill plates for some time now, using
rigid insulation instead.  My opinion is that if a bale wall has enough
water in it to need 'drainage' (from any source), those bales are goners.

The building official in Sonoma is citing it's recommendation in SB332 as a
good enough reason to require that it be there.  SB332 says, "There shall
also be a drainage plane between the straw and the top of the foundation,
such as a one inch layer of pea gravel."  Does anyone know of the intent of

More importantly, does anyone know of any testing as to why this might (or
might not) be a good idea?

Your thoughts (and/or Holiday Greetings) always appreciated,

David and Anni

*  *  *  *  *
Arkin Tilt Architects
Ecological Planning & Design

David Arkin, AIA, Architect
LEED Accredited Professional
CA #C22459/NV #5030

1101 8th St. #180, Berkeley, CA  94710

"There is no way to peace. Peace is the way."
- A. J. Muste

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