[GSBN] using loose straw insulation in roof

[John Straube]

The best material data I have collected from around the world only goes down to about
4 pounds per cubic foot (64 kg/m3) and, as a material, the R-value is not more than 10% different than at 8 and 12 pcf.

However, when you build walls, gaps can form between the plaster and bale and between bales and posts etc. which results in air movement that reduces R-value in the field.  Low density can make this more of a problem as can very stiff high density bales. Can be overcome by good workmanship, stuffing straw into voids, using good plastering techniques etc.

But this does not mean I would recommend even 4 pcf in an attic without coating it with clay


> On Oct 25, 2017, at 6:34 AM, Rikki Nitzkin <rikkinitzkin at gmail.com> wrote:
> 
> Hi!
> 
> I don’t know if you all remember, but not long ago I asked about the MAXIMUM density of a SB before it begins loosing thermal properties… most people agreed that we should not worry about a bale being too dense.
> 
> Now I ask about the opposite question: is there a minimum density?
> 
> The other day we were talking about using flakes of straw to insulate a roof. One of the builders insisted that is was important that the insulation cavity was filled with highly compressed straw, and another said that as long as the cavity was properly filled (leaving no big holes for air to circulate) that the density of the infill is not important, as the straw (loose or dense, but enclosed in the insulation cavity) impedes the circulation of air, and that is what insulates.
> 
> Can any of you technicians refer me to studies about insulation properties and how they relate to density? or at least clarify my doubt: Is it important to highly compact the insulation in the roof? and why… so I can explain it better.
> 
> thanks!
> Rikki
> 
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Dr John F Straube, P.Eng.
jfstraube at uwaterloo.ca
www.JohnStraube.com