[Greenbuilding] Subject: mounting rigid insulation above sloped framed un-vented roofs.

Corwyn corwyn at midcoast.com
Thu Jul 5 13:58:47 CDT 2012


On 7/5/2012 7:09 AM, Alan Abrams wrote:

> Ken Levenson, a PH consultant and owner of 4.75 High Performance
> Building Products, recommends (and sells) vapor barriers with variable
> permeability under the wall board.   Permeability drops in winter,
> helping to keep moisture out of the cavity (which could otherwise
> condense on colder, exterior surfaces).  Permeability increases in
> summer, allowing the cavity to dry to the interior.

Unfortunately, I couldn't find what it varies ON in the technical spec. 
  Unless it works by having an internal calendar, how the permeability 
varies would be important to know before betting your house on it.

Also, either I am reading the spec wrong, or it says: "Weight: 
4.4lbs/sf"  So a row weighs over a ton.  That can't be right.

Thank You Kindly,

Corwyn

-- 
Topher Belknap
Green Fret Consulting
Kermit didn't know the half of it...
http://www.greenfret.com/
topher at greenfret.com
(207) 882-7652






More information about the Greenbuilding mailing list