It's confusing as to why this was so well understood in commercial work yet we have the 2009 IRC still mandating vapor barriers. We designed the walls not with vapor barriers, but vapor "open" so that they would dry. I agree moisture problems are primarily due to bulk (rain) and air transport, we knew this years go and omitted the vapor barriers in commercial work.
#CANARI BARRIER PANT CODE#
In my opinion, I believe it is this misconception, and the code is wrong. I guess the confusion is then why the IRC still mandates Class I or II Vapor barriers, with Class III only permitted in certain circumstancese such as vented siding. We got rid of the poly in commercial work back in 1999 at least in my part of the world. In the residential work I have not much been involved with wall design, thank goodness, with all the opinions from everyone and their brother, so I was happy to find this building inspector who lowered his ego and made sense. (The solution to this problem is an air barrier, not a vapor diffusion retarder.)įor more information, see had a building inspector ask a builder why he installed poly on the interior of the wall vs just using the paint. Air leaks that allow moisture-laden interior air to enter the wall. Wind driven rain that gets past flashing or the WRB.Ģ. The two biggest causes of wet-wall problems are:ġ. Outward vapor diffusion has never been a significant mechanism for wet-wall problems. Requirements for vapor diffusion barriers (or vapor diffusion retarders) in our building codes were based on a misconception, not science. It would be helpful to those considering insulating walls of existing homes if commercially available paints were labeled with perm ratings." A I-inch-diameter vent at the top of the wall cavity is less effective than using these paints to keep the wall dry, but more effective than using vents at both top and bottom of the wall cavity. Two coats of interior semigloss acrylic latex, exterior acrylic latex, exterior soya-alkyd resin, or aluminum paint can be effective in keeping the moisture level of wood in the wall cavity below 20 percent even where 35 percent relative humidity is maintained. barrier subject to the climate of Madison, Wis., is likely to result in critical levels of condensation in the walls where mechanical humidification is used to maintain 35 percent relative humidity or higher. "Adding insulation to walls of an older house with no vapor. Here's an old study by the Forest Products Laboratory done in 1978 in Madison, WI on interior paint as a vapor barrier. Maybe people aren't using the plastic any longer and we just haven't caught on? If the paint weren't stopping the vapor where would the moisture escape to once it was trapped behind the drywall and in front of the plastic barrier? Doesn't it seem like a bad idea to let the moisture be held here? It seems it would be easier to handle the moisture inside of the house if it was obstructed from entering the drywall by the interior paint.
I'm questioning whether or not it is actually the interior paint that is serving this purpose of the vapor barrier or retarder. In this area many use poly over studs and joists/rafters before installing drywall.
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