RDH Building Science

The design and construction of multi-family buildings in the Lower Mainland of British
Columbia has come under increasing scrutiny due to the high incidence of water ingress and
resulting decay of materials in the exterior assemblies of these buildings. Most new buildings
and many of the remediated moisture damaged buildings are being built using “rainscreen” wall
assemblies, on the premise that that these assemblies are more tolerant of moisture and will limit
wetting to levels which can be accommodated by the building materials. Unfortunately, very
little data is available to determine how these assemblies actually perform in service. As an
industry, we require data on how the “rainscreen” wall assemblies, as currently being designed
and constructed, will perform on a long-term basis. Better knowledge of rainscreen wall
performance in service will also help identify opportunities for fine-tuning rainscreen assembly
design to make them more cost effective and durable.

This paper outlines the monitoring systems used in the study. Portions of the results are
presented that relate to anomalies of interest such as, the effect of overhang on wetting, the
results of unexpected moisture levels in the buildings, a comparison of the different cladding
systems used in the study, and a comparison of actual wind and driving rain conditions compared
with current design guidelines.

At the time this paper was written the monitoring program was approximately 60% complete.
Building 5 had not come online yet due to construction delays and only limited data has been
obtained from Building 4. As such, this paper does not include analysis of the results from these

The monitoring project was funded by the Homeowner Protection Office, BC Housing, and the
Canadian Mortgage and Housing Corporation.

RDH Building Science