Masonry Magazine September 2004 Page. 38
Drainage
Who would have thought years ago that when we talked about drainage, we needed to, first and foremost, discuss the airflow in the cavity wall?
After running a similar test on Mortar Net's Weep Vent product, Bupp says they weren't very satisfied with the results. "We went back and reformulated our Weep Vents, reconfigured the mesh a little bit, made a few changes and ended up increasing the airflow by about 36%," he says.
"We could have left them alone because they did fine as far as drainage," adds Lee, "but we're trying to get beyond that concept of just looking at drainage you look at drainage, you look at air flow, you look at all of the issues."
In addition to increasing airflow through the weep material, experts are now suggesting that weeps at the top of the wall will help attain good airflow and drainage.
"It's almost like trying to pour gas out of a gas can," Bupp suggests. "You know how they have that second valve letting air in so that you can pour gas out of the can. Once you open that second valve, the gas flows out of the can much easier. It was kind of like that concept in a way.
"Actually, vents at the top of the wall have been in use for a couple of years now," he adds. "Basically, the idea is that by having vents at the top and weep materials at the bottom, we get a circulation of air going through the cavity."
Roger Lingofelt, Owner of U.S. Wire in St. Paul, Minn., and maker of Cell Vents, agrees with this concept.
"It makes sense to get the air circulating," says Lingofelt. "I've got a job that we did here on a courthouse where the architect put vents everywhere, and I'm sure that was his thinking."
But won't that just introduce more moisture into the wall? "I have had that argument, and what I say to people is that it's pretty much a fact that moisture is going to get into that cavity," Bupp explains. "The general consensus seems to be that the benefits of having that additional airflow through the cavity to dry out the components outweighs the potential of getting more moisture in there through those vents."
Putting the Pieces Together
ONCE YOU HAVE ESTABLISHED the airflow, the rest of the pieces making up the complete drainage system can fall together:
* The air barrier stops the airflow from entering the building;
* One to two inches of air space keeps the air moving, drying out the cavity;
* Proper flashing sends water moving in the right direction; and
* A mortar collection device allows the weeps to stay clear at the bottom of the wall.