Waterproofing detail

The vertical or near-vertical continuation of the roof waterproofing above the general roof level at abutments, parapets, rooflight kerbs and penetrations. UK guidance calls for upstands of sufficient height above the finished roof surface, terminated with a flashing or capping so water cannot get behind the membrane.

A strip of impervious material, traditionally lead but also aluminium, zinc, copper or polymeric products, dressed over joints and junctions such as upstands, abutments and chimneys to shed water over the waterproofing below. Cover flashings are typically let into masonry chases and dressed down over membrane upstands.

Any element that passes through the roof waterproofing, such as soil vent pipes, flues, cables, plant supports and drainage outlets. Each penetration must be individually sealed, typically with upstands, sleeves, preformed collars or liquid-applied detailing, and penetrations are a leading location for leaks.

The overlap between adjacent sheets of roofing membrane or underlay where they are joined and sealed, by heat welding, solvent welding, adhesive, tape or bitumen bonding depending on the material. Lap integrity determines the watertightness of sheet systems, so minimum lap widths and the staggering of end laps are specified in system guidance.

A detail at a roof edge or gutter that projects the waterproofing beyond the supporting construction so water drips clear rather than tracking back under the covering. In felt roofing a welted drip turns the membrane down into the gutter, while preformed metal or GRP trims perform the same function in other systems.