External Above-Ground Waterproofing

About this course.

External above-ground waterproofing is demanding because the membrane has to do everything an internal wet-area membrane does — form a continuous, flexible, bonded barrier — while also surviving the full force of the weather and far greater movement, for decades, often with no easy access to inspect or repair it. A balcony, deck, roof, planter or podium is exposed to sun, rain, heat, cold, wind and, where trafficked, wear; it expands and contracts through large temperature swings; it moves as the structure moves; and it usually sits above occupied space, so a failure leaks directly into rooms below. All of this makes external above-ground work less forgiving than internal work, and it is why these areas are a leading source of serious, expensive building defects and disputes in Australia.

The first source of difficulty is weather and UV exposure. Australian conditions are severe: intense ultraviolet radiation, high surface temperatures on dark trafficable surfaces in summer, cold nights, driving rain, hail and, in some regions, salt and coastal exposure. Ultraviolet light degrades many membrane materials over time, making them brittle and prone to cracking unless they are either formulated and rated for exposure or protected from the sun beneath a covering. Heat and cold drive daily and seasonal expansion and contraction, cycling the membrane and every joint and junction relentlessly. A membrane that would last indefinitely indoors can fail quickly outdoors if it is not suited to the exposure.