We recently conducted some flow tests on wall panels containing MTI drainage planes against a wall panel with a WRB acting as a drainage plane. In all cases, from our economy Gravity Cavity drainage plane to our 10mm Sure Cavity drainage plane, the results were dramatic! All three MTI drainage planes allowed the two liters poured into their respective panels to drain almost as fast as it was poured in. In all cases the bulk of the water was out of the panel in seconds (except for some remaining dripping).
The control panel containing the WRB as a drainage plane was not very effective. Right from the start of the pouring, problems were noted. Water began to back up in the fill trough at the top, and pouring had to be delayed until some of the water could get down into the wall panel. When draining did finally begin, it was very slow. As in a real building envelope, when entrapped moisture can’t travel vertically down to escape, it migrates elsewhere, even horizontally. Water in the WRB panel found a way to force its way out the side of the panel and through a previously unnoticed hole in the front of the panel. Water also saturated the WRB and remained in it and in the wood for an extended period of time.
An effective drainage plane must maintain a permanent, predictable void to keep walls dry and safe. The Gravity Cavity and Sure Cavity panels clearly did this while the WRB panel didn’t. Dry building envelopes improve the health of building occupants, save energy (insulation isn’t ruined and less energy is used to dehumidify) and last longer. Take a look at our Gravity Cavity video and compare it to our WRB video on YouTube.