[GSBN] Straw bale at high altitudes (and snow against bale walls)

martin hammer mfhammer at pacbell.net
Fri Jul 11 18:57:35 CDT 2014


Hi Misha,

In terms of moisture concerns for strawbale walls, elevation in itself is
not relevant.  What matters is climate (precipitation, temperature,
humidity, wind), and how it relates to interior ³climate².  Higher
elevations do mean lower relative temperatures for the region (in all
seasons, 3-5 degrees F per 1000¹), so indirectly it matters.  But very low
outdoor temperatures beg for strawbale walls (just ask our Canadian
friends!).  As long as you employ normal good practices to prevent
relatively warm-moist interior air from condensing in the strawbale wall, by
using a vapor retarder on the inside face of exterior walls (the IRC
requires Class III vapor retarder (between 1.0 and 10 perms) in cold climate
zones) and by sealing penetrations on the inside face of these walls.

I agree with what everyone else has said re: the foundation issues.

Also the concern was raised about snow sitting against the bale walls.  I¹ve
never been convinced one way or the other whether this is a real or an
imagined problem.  Thoughts / questions include:

* When the snow-wall interface is below freezing, presumably nothing
detrimental occurs.
* When snow at the snow-wall interface melts (because all snow is melting or
because the snow at the interface melts because the wall surface is warm
enough) is a space created that allows drying of the plaster, and thus no
harm? 
* When the snow at the snow-wall interface melts, does it saturate the
plaster, which then wets adjacent straw causing degradation, and/or does
moisture in the plaster sometimes freeze and damage the plaster?

Does anyone have experience with snow against bales walls that answers these
questions?

Thanks

Martin 

Martin Hammer, Architect
1348 Hopkins St.
Berkeley, CA  94702
510-525-0525 (office)
510-684-4488 (cell)


On 7/11/14 8:40 AM, "Misha Rauchwerger" <misha.rauchwerger at gmail.com> wrote:

> I have a client that wants to build a straw bale house at 4000 feet in the
> Sierra Foothills.  They have been getting conflicting information about the
> wisdom of building with straw at that elevation.  In particular there is the
> concern about the effects of moisture in the wetter months, and possible
> condensation inside the walls.  They know about the need for big eaves, and
> permeable plasters, but have been swayed against the idea from a local green
> architect in town.  Please direct me to any research, or anecdotal evidence to
> support straw bale construction under these conditions, or maybe there is
> valid concern.  I have only built in the lower/dryer elevations on flatter
> sites.
> 
> They also share these concerns:
> 
> Their lot is sloped, so they would likely have to build a full walk-out
> basement on the lower level, and the living space on the upper level.  This
> means that the full lower level is built of concrete (probably Faswall or
> Durisol); will they would have to build out the lower walls to match the width
> of the straw bales?  How is this disparity in wall thicknesses usually
> resolved with the least cost/impact?
> 
> - With a walk-out basement, is it possible/reasonable to do a
> stepped-foundation on the lower level to minimize the amount of concrete used?
>  Or does the mixed use of concrete and post/beam and straw bale construction
> create unreasonable headaches in the building process?
> 
> Thanks everyone for your comments,
> Misha Rauchwerger
> builtinbliss.com <http://builtinbliss.com>
> 
> 
> 
> 
> 
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