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

[John Swearingen]

I believe that Dr.Strobe was talking about detailing for an extreme
condition.  This could be the climate ranges that he outlined, and could
also be for a very tall wall, where sun-driven vapor migration could involve
higher amouhnts of moisture.

John

On 3/12/07, David Neeley <dbneeley at gmail.com> wrote:
>
> 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.
>



-- 
John Swearingen
Skillful Means, Inc.
Design and Construction
www.skillful-means.com