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Re: GSBN:RE: 5 perms / no ventilation; and top-of-wall



Mark,

See my reply below.
Rene
On Mar 8, 2007, at 14:22, Mark Piepkorn wrote:

At 04:05 AM 3/8/2007, you wrote:
The general practice in Scandinavian countries is to have less
permeable interior finishes then outer... Another practice is that
air barriers including caulking when made are on the inner side
of the structure.

        Those are good practices of a sort that are seeping into
wider usage, thankfully, courtesy of info-sharing groups like this,
books with good technical info and details, increasing field
experience and lab testing, and better knowledge of building science
generally. A thousand hoorays to all of you.

        The worries discussed at the meeting were about some
already-built houses in the region that don't conform to current
understandings and best practices. The mean temperature in Vermont,
for instance, during the five winter months from November through
March ranges from 15F to 38F (-9C to 3C). The interior envelopes are
presumed to be reasonably airtight, and the interior finishes were
applied with an understanding of "the higher the permeability, the
better."

        Should the builders get ulcers laying awake at night
imagining moisture disasters in the making?

Maybe, it depends on the diurnal temperature swing. If it is small ie
almost steady state they could be in for trouble. If the swing is
substancial 5-10 degrees C I don't expect may problems. The other
factor is again if there are cold bridges in the structure. Problems if
they occur will first appear in the vicinity of the cold bridges. They
could function as an early warning system.