Lets not forget Dew Point Temperature in this discussion. I could use a good review of the calculations...... [log in to unmask] wrote:Alright, boys and girls, I have another pain-in-the-ass technical question, this time regarding vapor barriers and flexible membrane flashing inside masonry walls. I am working on a couple of c. 1950-60 NYC residential buildings, into which I want to stop water penetration. What I have recommended in the past is removal of face masonry (in both these cases, brick) and installation of flexible membrane flashing on the outer face of the backup wall (concrete block), followed by rebricking and installation of weeps, drainage mat, etc. The theory is that whatever water migrates inwards through the face brick will be stopped and drain down the face of the Bituthene, and out the weeps. One of my least-favorite contractors said yesterday that there have been concerns that sealing up an entire building in this way may prevent moist INDOOR air from passing through the wall and outwards, and that mold may grow as a result. What this alleged individual says is that they have installed one "course" of Bituthene at shelf angle level to drain water out and flash the shelf angles, and above that they install Tyvek so that the moist indoor air can pass through the Tyvek instead of being blocked by the Bituthene and being trapped forever inside the wall. This guy claimed that the Tyvek was sealed (including horizontal lap joints) and nailed or glued to the backup wall, so that condensation forms on the INSIDE face of the Tyvek. Seems to me that sealing the Tyvek, esp. at horiz joints, will trap moisture, too, and trap it at the INTERIOR face of the Tyvek, where you really don't want it. For the Tyvek to do you any good, it seems to me that the horiz. Tyvek joints have to be left open so that moisture that condenses will run down the interior face of the Tyvek and eventually be conducted to the Bituthene and drained out. OR am I full of shit about how condensation inside walls works, and specifically on which plane within the wall it condenses; I have a feeling that inside moisture condenses at a different plane within the wall than cold oudoor air condenses. Please advise, and thanks. Ralph Martin Skrelunas [log in to unmask] P.O. Box 184 New Canaan, Ct 06840 ph.:203.966.4483 / fax:203.972.1767