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<TITLE>FW: [GSBN] SB & Acoustics</TITLE>
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<FONT FACE="Arial"><SPAN STYLE='font-size:10pt'>John – The e-mail from 2010. - MH<BR>
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<B>From: </B>Martin Hammer <<a href="mfhammer@pacbell.net">mfhammer@pacbell.net</a>><BR>
<B>Reply-To: </B>"(private, with public archives) Global Straw Building Network" <<a href="GSBN@greenbuilder.com">GSBN@greenbuilder.com</a>><BR>
<B>Date: </B>Sun, 14 Nov 2010 08:00:31 -0800<BR>
<B>To: </B>"(private, with public archives) Global Straw Building Network" <<a href="GSBN@greenbuilder.com">GSBN@greenbuilder.com</a>><BR>
<B>Subject: </B>Re: [GSBN] SB & Acoustics<BR>
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Hello Sarah,<BR>
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Some years ago a strawbale highway wall was constructed in the state of Nevada. I’ve seen photographs and text written about it, but I can’t put my hands on either, even after doing a moderate internet search. I did find reference to this system of construction being used as an acoustic barrier in a Nevada Department of Transportation report. You can see it via the following downloadable link:<BR>
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<a href="http://www.nevadadot.com/reports_pubs/Research_Pubs/pdfs/ResearchReports/2001/01_006A_part1C.pdf">http://www.nevadadot.com/reports_pubs/Research_Pubs/pdfs/ResearchReports/2001/01_006A_part1C.pdf</a> <BR>
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On page D-2, “Hay Bales” are described as one of many “Previously Submitted Soundwall Systems”. Further on there is a matrix evaluating the different systems according to an array of criteria.<BR>
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I’ve often thought that strawbale walls would be great acoustic barriers on the side of highways. I don’t know how the Nevada wall has performed and weathered, but the challenges for these walls seem to be <BR>
</SPAN></FONT><OL><LI><FONT FACE="Arial"><SPAN STYLE='font-size:10pt'>that the wall’s height be adequately restrained against lateral loads from wind and earthquakes
</SPAN></FONT><LI><FONT FACE="Arial"><SPAN STYLE='font-size:10pt'>that the bales remain dry enough to avoid deterioration<BR>
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I have seen strawbale landscape walls by others where I know the bales rotted (a 10 year old wall with lime-cement plaster) because I did conclusive probing, or where I suspect the bales rotted because of a hollow sound. I’ve thought for some time that putting a ventilating “roof” on a plastered bale landscape wall would greatly improve its longevity. Or one can simply accept that the bales are just formwork for “structural” plaster and let them deteriorate, but that wouldn’t work so well for tall walls or acoustic barriers.<BR>
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The acoustic issues for a highway sound barrier are worth carefully considering. Some were mentioned by Derek and Graeme. I agree with most of their points. I’ll add a few things.<BR>
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</SPAN></FONT><UL><LI><FONT FACE="Arial"><SPAN STYLE='font-size:10pt'>Mass is an important element in acoustic barriers, but it attenuates mostly the lower frequencies. Transmission of higher frequencies can be diminished by less massive materials, such as straw bales. Here we’re talking about transmission <U>through</U> the barrier, not above or around it (as Derek points out). So extent of the barrier is important. <BR>
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</SPAN></FONT><UL><LI><FONT FACE="Arial"><SPAN STYLE='font-size:10pt'>The surface of the barrier, both its texture and it absorptive/reflective qualities, is important. So on a straw bale wall, a roughly textured clay plaster finish would absorb more sound, and the sound that was reflected would be more dispersed, as compared with a dense, smooth, cement plaster finish.<BR>
</SPAN></FONT></UL><FONT FACE="Arial"><SPAN STYLE='font-size:10pt'><BR>
</SPAN></FONT><UL><LI><FONT FACE="Arial"><SPAN STYLE='font-size:10pt'>There is a difference in acoustic performance between having an acoustic barrier on one side of a highway versus both sides. Having the barrier on one side creates a worse situation on the side without the barrier, because it imposes additional reflected sound on that side. Having the barrier on both sides creates back and forth reflectance. That can make the sound in between the walls (on the highway and its shoulders) rather unpleasant. Although I suppose we don’t really care (or care much less) about the acoustics on the highway itself. Having an acoustic barrier on both sides, with back and forth reflectance, can change the acoustic dynamics and the reach of the sound on either side of the highway, because the location and height of the “source” can change as it bounces off the walls.<BR>
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I do think a plastered strawbale wall provides a good balance of mass and insulation/absorption (if that’s an accurate way to state it) for an acoustic barrier, in a similar way that a plastered strawbale wall provides a good balance of mass and insulation for thermal performance.<BR>
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Those are my thoughts on the subject.<BR>
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Martin (bouncing off the walls) Hammer<BR>
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On 11/11/10 6:42 PM, "Sarah Johnston" <<a href="sarahjohnston@ihug.co.nz">sarahjohnston@ihug.co.nz</a>> wrote:<BR>
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</SPAN></FONT><BLOCKQUOTE><FONT FACE="Arial"><SPAN STYLE='font-size:10pt'>Hello!<BR>
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We've had an inquiry from a local road works company about using straw bale as a landscape wall for acoustical reasons along the main highway (keep in mind, in this neck of the woods...the main north-south road is two lanes only...).<BR>
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They have requested acoustical research and data. We have the information in Bruce's book, but I thought I would check to see if there has been any new testing or research done recently that you could share with us?<BR>
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Does anyone have experience with landscape walls along busy highways?<BR>
I'm questioning the overall long-term durability of this type of landscape wall. Your thoughts and input are all welcome.<BR>
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Many thanks!<BR>
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Cheers,<BR>
Sarah<BR>
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Sarah Johnston<BR>
Sol Design, Ltd.<BR>
50A Connolly Street<BR>
Geraldine New Zealand<BR>
03 693 7369<BR>
<a href="sarahjohnston@ihug.co.nz">sarahjohnston@ihug.co.nz</a><BR>
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