Introduction

One of the most important and problematic functions of walls is the control of rain penetration. The popular brick veneer wall system uses an exterior brick screen to resist water, with a cavity and water barrier to drain any water that penetrates the brick screen. The provision of a clear cavity and effective drainage in this form of construction is an important, if not critical, issue for moisture control. However, in field surveys it has been found that many cavities are obstructed by mortar dams and crossed by mortar bridges. Accumulations of mortar droppings at the base of the air space can completely block the drainage bath (i.e., the cavity and weep hole) allowing very little or no water to flow. The result can be moisture-related discolourations and deterioration, water leakage, corrosion and a reduction in thermal performance.

This study was initiated to look at two alternative solutions to ensuring a clear cavity. One alternative involves filling the cavity with an air and water permeable fibrous insulation (semi-rigid glass fibre) to reduce the effect of mortar droppings and mortar dams on the cavity (called the Zero-Cavity approach). The other alternative is to avoid blockage by preventing the mortar from entering the cavity space while at the same time ensuring the Drainage, Pressure-equalization, and Ventilating capabilities of the cavity (called the DPV approach). A prototype of a unique insulated sheathing being developed by Dow Chemical Canada was used in the DPV wall system. It is a rigid foam plastic, specially shaped with 12 mm deep by 100 mm wide drainage and ventilation grooves, protected from mortar intrusion by a plastic mesh. The bricks were laid tight against this proprietary board product. To provide a comparison with standard construction techniques, a Datum wall system with a clear cavity was also included in the study.

• cavity wall : zero cavity and DPV wall by CMHC
• PV/T