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GSBN: Re: STC of Straw bales

--On Wednesday, October 16, 2002 10:47 AM +0200 Coralie & Andre de Bouter m.ep@... wrote:

In France there is a vicous rumour going arround that SB walls are
a poor sound insulator. Arnaud Cauwel wrote a report for his school
of architecture in which he claimed that straw (because of its low
mass) insulates poorly. No numbers or test data is given.

This is like saying birds can't fly because they don't have feathers: wrong data, wrong theory. While straw bales are not terribly dense, they do contain substantial mass. A plastered strawbale wall will have about half the weight/mass of an adobe or stone wall in an equivalent structure (per square foot/meter of wall surface, or per lineal foot/meter of a wall of the same height). A plastered strawbale wall will weigh more than twice what a brick wall weighs. There is a great deal of mass there.

In attenuating sound, mass is important. However, thickness also matters. The same amount of mass will cut the sound more if it is deployed at lower density, in greater thickness. Rigid, elastic materials (like steel) will transmit sound more effectively than softer materials with multiple internal planes of reflection, like foams. Strawbale walls score well on all three counts: high mass, great thickness, and soft, amorphous material.

Hard plasters do lead to echoes, so the inside of a SB house may not be the perfect environment for a musical recital. The non-strawbale parts of a structure, such as roof, windows and floor, can have a significant influence on sound performance. But if other things are equal, a SB house will have sound insulation properties superior to most common building materials, and on par with the best.

Still, our French SB friends have a problem. It's often hard to fight stupidity and prejudice with numbers or logic. The people who are willing to spend a few minutes in a SB house will be convinced.

Derek Roff
Language Learning Center, Ortega Hall Rm 129, University of New Mexico
Albuquerque, NM 87131  505/277-7368 fax 505/277-3885
Internet: derek@...