[GSBN] windscreen

[Jim Carfrae]

The missing reference should have been for Matthew Summers in Bruces book - (Summers (2006) in King, B. (Ed). Design of straw bale buildings. Green Building Press, San Rafael. pp. 161-172.)
This is a generally accepted upper limit, and a sensible one in my opinion.
Reality is more complicated - straw can survive moisture levels up to fibre saturation point (37%) for a period of months as long as it is able to dry back.
However, in a cool humid climate I would sugest that if there are continuos steady moisture levels in excess of 20%, then there is likely to be a problem with the wall (or it is very exposed).
I have no experience of straw in hot humid climates, but looking at published isotherms the results at 30 degrees C aren't a great deal higher than at 20 degrees (a couple of percent higher at a given RH). 

Jim

Jim Carfrae
PhD Research Student

Room 119, Reynolds Building
University of Plymouth
Drake Circus
Plymouth
PL4 8AA

jim.carfrae at plymouth.ac.uk
07880 551922
01803 862369
________________________________________
From: GSBN-bounces at greenbuilder.com [GSBN-bounces at greenbuilder.com] On Behalf Of John Swearingen [jswearingen at skillful-means.com]
Sent: 24 January 2011 18:23
To: jfstraube at gmail.com; (private,  with public archives) Global Straw Building Network
Subject: Re: [GSBN] windscreen

Thanks, that's interesting data.  The paper mentions 25% as the upper limit of moisture content for bales with a source notation of [8].  However, [8] is missing from the paper.  What IS the upper limit, and how does this vary with temperature?

Thanks,
John

On Sat, Jan 22, 2011 at 12:36 PM, John Straube <jfstraube at gmail.com<mailto:jfstraube at gmail.com>> wrote:
Excellent paper. Useful addition to the arsenal.

Sent from my BlackBerry®

-----Original Message-----
From: Jim Carfrae <jim.carfrae at plymouth.ac.uk<mailto:jim.carfrae at plymouth.ac.uk>>
Sender: GSBN-bounces at greenbuilder.com<mailto:GSBN-bounces at greenbuilder.com>
Date: Sat, 22 Jan 2011 13:32:00
To: (private, with public archives) Global Straw Building Network<GSBN at greenbuilder.com<mailto:GSBN at greenbuilder.com>>
Reply-To: "(private, with public archives) Global Straw Building Network" <GSBN at greenbuilder.com<mailto:GSBN at greenbuilder.com>>
Subject: Re: [GSBN] windscreen

Thanks, John.
I wrote a paper for a conference in 2009 with these findings in it.
I don't know if I can attach it to this email to make it available to all, but I'll try.

Jim

Jim Carfrae
PhD Research Student

Room 119, Reynolds Building
University of Plymouth
Drake Circus
Plymouth
PL4 8AA

jim.carfrae at plymouth.ac.uk<mailto:jim.carfrae at plymouth.ac.uk>
07880 551922
01803 862369
________________________________________
From: GSBN-bounces at greenbuilder.com<mailto:GSBN-bounces at greenbuilder.com> [GSBN-bounces at greenbuilder.com<mailto:GSBN-bounces at greenbuilder.com>] On Behalf Of John Straube [jfstraube at gmail.com<mailto:jfstraube at gmail.com>]
Sent: 22 January 2011 13:03
To: (private, with public archives) Global Straw Building Network
Subject: Re: [GSBN] windscreen

Well Jim that is darn useful stuff!   have you done a paper or something on this?  Would be great to have this info to spread around.



On 2011-01-22, at 5:25 AM, Jim Carfrae wrote:

> As part of my research into the moisture performance of SB in a Temperate Maritime (Damp) Climate , I've monitored two structures where a direct comparison can be made between a plain lime rendered section of wall adjacent to a section of the same wall protected by a ventilated timber rainscreen.
> (Plain lime wall = 3 x 12mm coats. Rainscreen = 1 x 12mmm scratch coat, 25mm vented void, permeable membrane, 25 mm vented void, vertical timber boarding with 5mm gaps)
> In each case the average moisture content of the straw just behind the render was between 3% and 4% lower (typically 17% behind plain render, 13% behind rainscreen)
> This is an apreciable difference, especially as this was not a particularly exposed site. If there was significant driving rain I would expect the difference to be higher.
>
> To reinforce what John Straube said - It has to be vented top and bottom.
>
> Jim (moist) Carfrae
>

Dr John Straube, P.Eng.
Associate Professor
University of Waterloo
Dept of Civil Eng. & School of Architecture
www.buildingscience.com<http://www.buildingscience.com>

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John Swearingen
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