[Greenbuilding] Open Cell Failure

[RT]

On Thu, 30 Jan 2014 10:09:28 -0500, conservation architect  
<elitalking at rockbridge.net> wrote:

> My statement I believe my statement was incorrect.  The high  
> concentration of vapor should increase the dew point temperature,  
> similar to a high relative humidity.  A higher dew point temperature  
> increases the vulnerability of condensation and rotting.


I think that the entirety of this thread has been very confused/confusing.

A higher moisture content in the air is by definition, the same as higher  
humidity.

It should be obvious then, that for a given temperature, if one increases  
the moisture content of that air, one increases the likelihood of  
condensation (ie dew point) occurring at the periphery regions where  
pockets of still air are likely to created adjacent to cool  or cold  
surfaces .

Also, even though EPS may be effective as an air barrier material, it's  
probably not a good idea to encourage moisture transport via vapour  
diffusion into the material even if for no other reason being that its  
value as insulation is decreased when it's full of moisture.

The other question is how one gets that moisture back out again once it  
has condensed within the EPS.

ie That liquid moisture would need to be turned back into vapour before it  
would be cooked out.

Since  the EPS is supposedly a thermal insulation which by definition  
retards heat transfer, how does one encourage sufficient heat loss from a  
heated interior to first turn the condensed moisture in the EPS into  
vapour and drive it out into the ventilation air space that Eli wants to  
provide on the outside of the insulation and under the roof sheathing ?

A better strategy would seem to be to simply minimise moisture transport  
into the EPS in the first place.


Or if the climate is such that one hopes that the condensed moisture in  
the EPS will dry to the interior via sun-driven inward vapour drive, is it  
really desirable from an healthy indoor air perspective to have stagnant  
water that has been hanging around in the dark interstices of the building  
materials for who-knows-how-long, dumped into the interior air that the  
occupants breathe ? I don't think so.
-- 
=== * ===
Rob Tom					AOD257
Kanata, Ontario, Canada

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