[Strawbale] On moisture

[Jeff Ruppert]

Mark,

Thanks for the x-post. I have to lean toward this kind of position in 
our climate. We still have yet to identify any moisture problems related 
to indoor humidity levels. I have always believed that our biggest 
enemy, no matter what type of plaster (again, in our climate, Colorado) 
is exterior wetting. John Straube in a past TLS put this in perspective 
by estimating the amount of cellulose in a bale wall being 4 or 5 times 
(loosely quoted) than that of a wood framed wall. Therefore being able 
to hold a similar increase in moisture, safely.

With that said, I still also believe in the rules of permeability of 
each plaster skin. Relative to each other, they should be chosen based 
on permeability given your climate.

It is clear from many stories that particular materials are better at 
buffering humidity, such as earthen plasters in a bathroom vs. drywall 
or tile. I think we are just beginning to place all of our choices into 
a continuum based on their buffering abilities. Some are better then 
others. And there are a handful that perform relatively equally in 
different climates. I would venture to say, based on the numbers below, 
that the substrate is less important than the facing or render. Bale 
walls are statistically the same as Durisol. What is similar is their 
cellulose content. What is different is their lime content. Durisol 
obviously has cement (basically lime) mixed in, but is not much better.

I love the scale of these numbers and the percentages! It really puts 
much of what we spend out time talking about in perspective.

Jeff



Mark Piepkorn wrote:
> Oldish news with a friendly face.
>
> http://markbrinkley.blogspot.com/2007/07/new-methods-of-handling-humidity.html
> Excerpts from the webpage:
>
> - - - - -
>
> How should we Handle Humidity?
>
> ...The fact is that a detached house, which can 
> weigh anything between 50 and 200 tonnes, 
> depending on size and construction methods (and 
> that's excluding all the foundations), could be 
> holding as much as 10 tonnes of bound water 
> within the walls, floors and roofing, and a lot 
> more within the fixtures and fittings as well.
>
> What does 10 tonnes of water look like? Due to 
> the miracle of metricated measurements, 10 tonnes 
> of water turns out to be 10m3 in volume, about 
> the size of a small bedroom, or perhaps 70 
> bathfulls, if you prefer that. It also turns out 
> to be 10,000 litres, which is the amount of water 
> a typical household uses in about two weeks, or 
> around 1500 flushes on a 6-liter low flush toilet...
>
> ...The fact that there is over a thousand times 
> more water bound up inside the building than 
> there is floating around in its airspace just 
> doesn’t come into the equation, despite the fact 
> that everyone agrees that moisture levels within 
> a building are constantly changing. Doesn’t it 
> seem strange that we should spend so much effort 
> and energy expelling 10 litres of water vapour a 
> day from our homes, when they are 10,000 litres 
> of water already sitting in the fabric?
>
> There are alternative water vapour management 
> strategies out there. The best established one 
> hails from Germany and it consists of fitting 
> highly permeable materials to be used as a 
> reservoir to store moisture, with a view to 
> letting it be evaporated back inside when 
> conditions allow. In Germany, it is seen as part 
> of the Building Biology movement and they regard 
> the use of humidity-buffering materials as one of 
> their key principles. Needless to say, they 
> regard the use of mechanical ventilation as an 
> anathema. A lot of building scientists regard the 
> Baubiologists as cranks, but there was some 
> independent testing of their humidity buffering 
> principles carried out in Canada in 1997 by Straube and Burnett ...
>
> ...They looked at the water vapour permeability 
> of a whole range of products and estimated the following sorption ratings:
>
> • Plasterboard painted with emulsion - score 40
> • Concrete, unfinished – score 90
> • Brick, natural finish – score 110
> • Softwood, unfinished – score 150
> • Strawbale behind lime plaster – score 240
> • Durisol board behind lime plaster – score 250
>
> They reckoned that anything with a score of 50 or 
> higher would work as a humidity buffer. They also 
> pointed out that such walls work automatically, 
> don’t break down and require no energy to operate...
>
> - - - - -
>
>
>
> Mark Piepkorn
> www.potkettleblack.com
>
> Wouldn't this be a wonderful world if insecurity
> and desperation made us more attractive?
>    - Broadcast News
>
>
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