Assessment of Roof Drainage Using 3D Laser Scanning

Ponding occurs when water persists on a roof surface for more than 48 hours after the most recent rain event has ended (NRCA). The ponding load is increased due to the buildup of water induced by the deflection of the roof structure (ASCE 7-16). Ponding can occur for a variety of causes, including deck deflection, poor drain location, improper tapering insulation design, obstructed or blocked flow, clogged drains, or drainage capacity that has been surpassed. Ponding can cause aesthetic and performance issues, as well as ponding instability and potential roof failure, if it is not treated. There are currently no globally accepted criteria for measuring ponding water. In addition, there is no practical or precise way for determining the degree and location of ponding.

Laser Scanning in 3 Dimensions

3D laser scanning is a long-established technology that may be used to construct a very detailed and accurate 3D model of a structure’s rooftop. It employs light rays to precisely pinpoint objects in three-dimensional space.

To cover the region of interest, many scans are performed across the building’s rooftop. Each scan generates roughly 60 million data points and covers about 5000 square feet. After that, the images are stitched together to form a single 3D model that can be used to evaluate roof slopes, water flow direction, tapering crickets, and tributary areas.

It is feasible to anticipate not just where water will drain to, but also where it will accumulate along the route, using flow modeling. This data is crucial for determining if a roof will succumb to ponding instability and developing a repair strategy to reduce the ponding load. This repair plan may include the installation of additional drains in key locations to give optimal relief, as well as the filling in of depressions with additional material to ensure a favorable slope towards the drain.


3D laser scanning can assist discover faults that aren’t visible to the naked eye, save money on repairs and alterations, and ensure that projects are finished on time and on budget. A project can be completed without delay and with increased confidence if faults are identified early, either before the roof is built or prior to re-roofing.

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