Flat Roofing & Waterproofing in Sydney

Fall is everything

A flat roof needs a minimum fall so water runs to the outlets instead of sitting in puddles. Ponding water finds every tiny weakness in a membrane, stays there working at it, and grows algae and debris that block drainage further. Many leaking flat roofs we see were simply built dead level or have sagged over time.

Correcting the fall might mean tapered insulation, packing the substrate or rebuilding the deck to drain properly. It is not glamorous work, but it is the foundation of a flat roof that does not leak, and no amount of membrane fixes a roof that ponds.

Membrane options

Flat roofs are waterproofed with a membrane rather than overlapping sheets. Options include liquid-applied membranes that cure into a seamless coat, torch-on bitumen sheets lapped and heat-welded together, and single-ply sheet membranes. Each suits different situations, decks and budgets, and each has its own detailing at upstands and outlets.

The joints, corners and penetrations are where flat roofs leak, not the open field. Whatever membrane we use, the care taken dressing it up walls, around pipes and into outlets is what determines whether it stays watertight.

Box gutters and outlets

Flat roofs often drain into internal box gutters and outlets rather than eaves gutters. Because these sit within the building, a blockage or an undersized outlet floods the ceiling instead of spilling harmlessly over the edge. We size outlets for Sydney's downpours and fit overflow provisions so a blocked drain has a safe escape route rather than backing up inside.