Water accumulation is prevalent on flat roofs, which doesn’t mean well for your roof health. It results in different issues, such as organic debris buildup and plant growth on the roof.
The most effective way to prevent water accumulation is to install a roof with proper slope and drainage. While you are responsible for ponding water on your roof, controlling water accumulation on your new or repaired roof is in the hands of your roof system designer. Your roof designer, which in most cases can be your roofer, is responsible for following the requirements to prevent drainage issues that can lead to water accumulation on the roof and its components.
It is worth noting that your roofer cannot eradicate ponding water, and some degree of ponding is acceptable by NRCA and roof system manufacturers. The only time ponding is unacceptable is when it lasts more than 48 hours, which can affect the roof’s long-term health.
According to NRCA, the criterion for determining the proper slope for drainage is that the roof dries within 48 hours after rain. Besides this, other building codes have slope requirements for membrane roof systems. For example, International Building Code (IBC 2012) Roof Coverings state that all membrane roof covering systems be installed a one-quarter inch vertically in 12 inches horizontally (2 percent slope) for drainage. Only coal-tar built-up roofs are exempted from this requirement.
This is the same requirement for previous IBC editions. Also found under this section are requirements for reroofing. The section states that the materials and application method for reroofing should meet the same requirements for new installations. However, the section doesn’t mandate one-quarter inch vertical in 12 inches horizontal for roof systems with existing positive roof drainage.
The section also makes provision for secondary drainage. It states that secondary drainage should be provided if the primary drains allow water buildup for any reason, and the roof drains or scuppers should provide the drainage.
Going further, IBC 2012 Roofing Coverings also requires roof drainage systems to comply with International Plumbing Code. While previous versions of the IBC codes don’t provide requirements for secondary drainage, they also emphasize following IPC requirements.
Since all editions of the IPC contain the same secondary drainage requirements as the IBC 2012 and IBC 2009, the requirements stated above for secondary drainage have been effective, only that it has not been implemented into the IBC section until 2012.
As a homeowner or business owner, hiring a roofer that complies with these requirements is necessary, so you comply with the regulations and don’t fall victim to ponding water. You certainly want to avoid finding yourself in a situation where the primary drains have become blocked and the accumulating water has no way to drain from the roof. In some instances, this can cause a catastrophic failure of the structure or pronounced leaking inside the building.
At HKC, we are knowledgeable about these requirements and carry out our jobs accordingly. We outline and discuss these requirements and others with our customers, so they also understand what the necessary regulations require regarding roof drainage.
We have an A+ Rating from the Better Business Bureau and are part of the National Roofing Contractors Association, serving our Cincinnati and Northern Kentucky area neighbors.