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Re: [OM] OT - Air source heat pumps and related matters

Subject: Re: [OM] OT - Air source heat pumps and related matters
From: Mike Lazzari <watershed@xxxxxxxxxxxxxxx>
Date: Thu, 06 Dec 2012 11:31:16 -0800
> I've worked on a half-dozen such buildings. They are quite common in 
> Permaculture circles.
>
> In our climate, straw bale is often combined with other natural building 
> techniques, such as cob (clay-straw matrix) or light clay infill (wood chips 
> or straw coated with a clay slurry). Typically, one would use straw bale for 
> the north wall for its insulation value, and cob on the south wall for direct 
> solar gain and thermal mass.
>
> Straw bale construction can yield R-36 walls -- about three times what you 
> get in stick-frame-fiberglass construction.
This house uses bales all around with light straw/clay infill and cob 
finish. Second coat is mostly finished and drying right now. Lots of 
fans necessary this time of year. A bit of lime and linseed oil will be 
added to the final coat for a more durable finish.

Typical stick walls around here start at R21 and go up. 22" thick straw 
walls are well above that for sure.

One of the most difficult issues was how to address the seismic load 
without unduly interfering with the baling. We opted for heavy duty 
steel strapping all around in addition to anchors to the foundation.

> That is very true about the fire resistance. However, there is the
> concern about fire inside the wall and the ability to isolate it
> without it spreading throughout the structure. Same situation with old
> stick-frame construction where vertical fire-breaks were not placed
> inside the walls. Is there any concern or means of addressing the
> worry about the fire going anaerobic?
Well, there are breaks in the walls that would act as traditional fire 
blocking. Basically soffits to isolate the bales from the ceiling 
insulation and ventilation (moisture source) and also to attach the 
strapping needed to bind the bales into place. They also support bales 
over window and door openings..

The only potential source for a smoldering fire would be at electrical 
boxes but these will be as per code and surrounded by the first coat of 
light straw/clay. Pretty inflammable.

RE: sprinkler system. We don't meet the minimum water requirements. And 
frankly a sprinkler would be relatively ineffective in a mud hut (that's 
what we call it) with cement slab floors.

My chief concern is for a fire during construction and we have 
construction insurance. Not cheap.

Mike
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