[Strawbale] window construction

[Robert Tom]

On Thu, 17 Apr 2008 17:11:58 -0400, Dave Howorth <dave at howorth.org.uk>  
wrote:

> My first question is about thermal bridges. All the drawings I've seen
> use a timber mount/buck/rough frame to connect the window to the wall.
> Doesn't this cause a thermal bridge? (especially if the window frame has
> been detailed with a thermal break) Are there any construction details
> that avoid this?
>
> My second question is about cutting openings in walls. I've seen a few
> mentions of cutting window openings after the wall has been built and
> plastered, but I haven't seen any detailed descriptions. So I'm left
> wondering such things as: do the openings have to follow bale boundaries
> or can they be made arbitrary sizes? If arbitrary, what stops the cut
> bales disintegrating? What linings, flashings, framings, plaster etc
> detailing is used?

Dave;

On the first point re: thermal bridges

Yes, you're correct.
A timber buck/rough frame can represent a thermal bridge but only if you  
detail it as such.

The means to avoid creating that thermal bridge would be the same as with  
any other wall system and that is, as you imply, by including a thermal  
break. The most obvious first step towards that end is simply to not  
utilise a solid lumber, full wall-width buck and insulate.

WRT the second question re: cutting door and window openings after first  
plastering the bales, IMO that was simply an ill-conceived idea from the  
get-go and would best be avoided. About the only point on the "plus" side  
for the idea was that it was more expedient for building contractors... ie  
get in and get out more quickly.

On the negative side, IMO , firstly it demonstrates a disrespect for the  
materials and the labour that went into making the cut-out section,  
treating both as "commodities" and disposable at that.

Second, it makes for a situation which is extremely difficult to flash and  
seal in an effective fashion, which ultimately leads to  
performance-related problems and failures later on for the homeowner and  
that, is disrespectful of the homeowner.

Third, using an abrasive blade to cut through oftentimes  
metal-mesh-re-inforced Portland cement plaster creates an incredible  
amount of gritty, permeates-everything, destructive (ie to motor bearings)  
and harmful-to-respiratory-systems dust... and creates sparks that have  
the potential to ignite any loose straw, or worse, drive hot molten metal  
into the straw where it would go unnoticed and could cause smouldering  
straw for a long time after.

Fourth, pounding on a newly-plastered wall to knock out the cut-out  
section is an excellent way to introduce cracks into otherwise good  
plaster.

As that Monty Python character once said in a cockney accent: "Need I say  
more ?"

-- 
=== * ===
Rob Tom
Kanata, Ontario, Canada
< A r c h i L o g i c  at chaffY a h o o  dot  c a >
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