External Wall Weatherproofing Design

About this course.

External wall weatherproofing failures are among the most common and costly building defects because walls are exposed to relentless wind-driven rain over large areas and many junctions, because a single poorly designed or built detail can admit water that then spreads and does damage far from the entry point, and because the damage is frequently hidden inside the wall — rotting, corroding and growing mould for months or years before it becomes visible, by which time the repair is major and expensive. In other words, walls face a large, continuous water load; they have many vulnerable points; and their failures are slow, concealed and cumulative. Understanding why they are so prevalent is the motivation for designing them properly.

Walls face a large and relentless water load. An external wall is a large surface continuously exposed to the weather, and in much of Australia that means significant wind-driven rain: rain is not simply falling vertically past the wall but is being blown horizontally at it, and even driven upwards under eaves and around corners. Over the life of a building the wall is wetted countless times, and every square metre and every junction must cope with that load. Unlike a roof, which sheds water by slope, a vertical wall must resist water that is being pushed directly against and into it. The sheer scale and persistence of the exposure means any weakness will eventually be found by water.