A flat roof is not intended to leave water without a route to an outlet. If you notice recurring pooling, its cause should be assessed before selecting a correction. Drainage must be considered alongside slopes, outlets, obstacles and deck condition. Installing a new membrane does not automatically change how water moves across the roof.
A blocked outlet, a low spot, an awkward junction or movement in the deck can create different situations. Photos taken after rain from a safe location, and a record of what you observed, can help explain the problem. An on-site assessment considers the route to the outlets and what needs further investigation before choosing a solution.
Consider a suitable slope correction
In some assemblies, tapered insulation can help direct water toward drains. Its layout must account for available heights, upstands, rooftop equipment and insulation needs. Panels are not selected independently of the roof around them. The design needs to remain compatible with the deck and the selected roofing system, including details at edges and penetrations.
Coordinate drainage with replacement
Replacement is an opportunity to discuss drainage defects and the scope of a correction. Drain locations, transitions and details around equipment should be considered together. If structural movement or a structural alteration is involved, an appropriate assessment is needed before defining the work. A drainage proposal should identify the intended correction and any conditions that still need confirmation.
Explore the assembly and technical details
60 mil TPO, Leister automated welding and prefabricated accessories: discover how the elements work together.
Not by itself. The membrane provides the waterproofing surface; water flow also depends on slopes, the deck and outlets. These components need to be considered together.
Does correcting slope mean rebuilding the structure?
Not always. Some corrections use tapered insulation. Other situations may need further investigation or more extensive work. The appropriate solution depends on the building conditions and selected system.
Is this the same as a pitched roof?
No. This page addresses drainage on flat or low-slope roofs. For a pitched roof with shingles, visit our dedicated page to discuss the covering and appropriate work.
