[Strawbale] 5 perms / no ventilation; and top-of-wall (Mark Piepkorn)

[David Neeley]

John,

In the original post, Dr. Straube was quoted as saying: "The top seal
of the wall needs to be an air barrier, and not a vapor barrier."

Does this mean you disagree?

I do agree totally that adequate attic ventilation is a sine qua non
for a well-designed and constructed house. Although I have not yet
gotten to the detailed design of the roof for the house I will build,
at the moment I am leaning toward either a ridge vent or solar powered
vent fans for exhaust coupled with well distributed soffit vents for
intake. The soffit vents and the normal ventilation through the
exhaust would seem to draw any such moist air up and out of the house.

My question, based upon the original Strabe comment, was whether Tyvek
or one of its competitors might actually be useful to give such an air
but not moisture barrier used in that position. I am well aware that
it isn't a great idea to use it to wrap houses, but as I do not plan
on doing that it isn't a big deal.

Of course, since I live in a cooling climate, I assume that the advice
for permeance should be backwards in this area compared to the heating
climate advice that this exchange has focused upon?

David

On 3/12/07, John Swearingen <john.skillfulmeans at gmail.com> wrote:
> Just to complicate things, you also don't want vapor from your walls to go
> up into an unventilated area of the roof/ceiling; moisture could accumulate
> there and cause problems. If there were such places (and it's not a good
> idea to have them) then Tyvek would allow some accumulation of moisture and
> that would therefore be a Bad Thing.