RE: [GBlist] Re: Wall permeability

["Ralph Bicknese" <ralph.bicknese@christnerinc.com>]

Kirsten:

I second Lewis' opinion.  I have had good results with the approach he
suggests.  I also rely on an interior air/vapor barrier and the air-to-air
heat exchanger/home ventilator to exhaust my bathrooms, in addition to
providing general ventilation.  I rely on a separate clothes dryer exhaust
and stove/oven exhaust by conventional methods of exhaust fans (separate
from the home ventilator).
As Lewis suggested there are two main points of view on the subject.  One is
the vapor barrier approach where the interior walls and ceiling are wrapped
with a vapor barrier with a low perm rating (it resists the flow of moisture
and gasses to pass through it).  This is usually accompanied by an
air-to-air heat exchanger/whole building ventilator to provide adequate
fresh air.
The other approach is to use a tight interior building skin that will not
let air to blow through it but will permit some exchange of gasses into or
through the wall.  Joe Lstiburek and the people at Building Science Corp.
are among those promoting this concept.  However, the details I looked at
(and checked again today) by Building Science Corp. (for buildings in cold
and semi-cold, warm climates) show an outside layer of foam insulation that
is sealed at the joints.  So, it would not really allow the gases from
inside to get outside, as the foam would act as a vapor and gas barrier and
trap both within the building envelope.   The approach of placing the vapor
barrier on the outside of a building in a cold climate is in opposition to
what I have been taught and practice.  I could go on about this but will
leave it at that. I am not familiar with the details that would actually
allow the gasses to pass.  But, an airtight drywall approach, without foam
on the exterior, would certainly allow more gasses to pass through the wall.
Other insulation would have to be increased to provide thermal performance
equivalent to one with foam on the exterior. Perhaps this approach is
similar to the one the proponents of baubiology are suggesting.
Cheers,
Ralph Bicknese

-----Original Message-----
From: Lewis J. Matt PhD [mailto:lmatt@alltel.net]
Sent: Wednesday, January 16, 2002 6:06 PM
To: greenbuilding@crest.org; kir@declan.com
Subject: [GBlist] Re: Wall permeability

-----Original Message-----
From: Kirsten Flynn [mailto:kir@declan.com]
Sent: Wednesday, January 16, 2002 11:30 AM
To: greenbuilding@crest.org
Subject: [GBlist] Wall permeability

Dear Kirsten:

The concept of a wall film that is selectively permeable to hazardous gasses
is quite intriguing.

I have good results with current technology by using an 8 mil vapor barrier
on the inside and a water vapor transparent, wind resistant wrap on the
outside of conventionally framed and insulated structures with an air to air
exchanger to ventilate the interior.  The vapor barrier keeps excess
moisture from permeating the insulation and reducing its insulating
properties, and the exterior wrap allows moisture to escape the insulation
but reduces the amount of air "blowing" through the insulation which can
also reduce its effectiveness.  Air exchangers can take care of the
hazardous gasses and the moisture without creating a thermal imbalance.  Air
exchangers can be powered or rely on a roof mounted vent stack for "pulling"
old air out of the building and new air in.  As far as moisture is
concerned, I have had good results directly venting bath and cooking
moisture and odors at their source with an exhaust fan that is turned on and
off as needed.  The shower and the gas stove are the two devices in a home
that generate the most moisture - and I don't want to give up either!  :-)
Note: *unvented* clothes dryers are also major moisture polluters.

If you have adequate vapor barriers and insulation ventilation with properly
sized heating / cooling, the in-the-wall dew point becomes insignificant in
a vented home.

Lew Matt


Synergistic Solutions: Alternative Septic and Energy Systems
Lewis J. Matt III, Ph.D., C.S.E.O.



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This greenbuilding dialogue is sponsored by REPP/CREST, creator of
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______________________________________________________________________


______________________________________________________________________
This greenbuilding dialogue is sponsored by REPP/CREST, creator of
Solstice http://www.crest.org, and BuildingGreen, Inc., publisher of
Environmental Building News and GreenSpec http://www.BuildingGreen.com
______________________________________________________________________