Properly designed commercial roofs always feature efficient drainage systems that quickly move water from the roof surface into drains or gutters. Ideally, a commercial building’s roof drains water off the roof entirely within 24 hours.
Even when all other commercial roofing elements perform well, an inefficient drainage system can compromise the entire building’s integrity in various ways. For example, water pooling may cause severe leaks which damage the roofing system and building interior, while water collection could overload the roofs’ weight capacity leading to a collapse.
Some commercial and residential roofing systems elements are the same, such as the type of materials used. However, aesthetically, the two systems can be very different.
Commercial flat roofs can be more resistant to environmental factors such as hurricanes and freak storms than a sloped roof. Still, its main challenge is draining water completely to avoid moisture buildup leading to leaks and mold or mildew growth.
Let’s look at five essential things you should know about commercial roofing drainage.
1. The Function and Essence of Commercial Roof Drainage Systems
Commercial building roofs have a slight pitch design to create positive drainage and direct water towards the drains. Commercial building architects know water collection can overload a roof’s weight capacity if it does not drain fast enough. Thus, they add backup drainage to mitigate this problem.
Positive drainage should dry your roof entirely within a day or two after rain, so if you see ponding, you should have a roofing contractor assess your drainage system.
2. Types of Commercial Roofing Drainage Systems
There are primarily two drainage systems suitable for commercial flat and low-slope roofs:
- Gravity Drainage: It relies on gravity to move water from your rooftop to the ground. It features four sloping drain segments connecting to an interior drain to carry water down and outside the building. The drainage system relies heavily on interior drains, similar to kitchen sinks or showers. It’s suitable for commercial roofs with a surface area of 150m² or less per drainage point.
- Siphonic Drainage: The drainage system has a baffle on each drainage point to prevent air from entering. Consequently, this creates lower atmospheric pressure inside the pipes than the outside environment, so water entering the drain meets an area of lower pressure which pulls it in faster than gravity would alone. It drains water 100 times faster than a gravity system and is suitable for large commercial buildings such as malls, factories, or warehouses.
3. Parts of Commercial Building Roof Drainage Systems
The two drainage systems above have similar components as explained below:
- Interior drains: These commercial roofing drains are similar to those in your bathroom or kitchen sink. Roofers place them in specific locations to collect the most water and direct it through a system of pipes until it reaches the ground or street. Different commercial roofs might require slightly different interior drains; for example, high-capacity or duel-outlet drains.
- Edge drains: These drainage systems collect water at the edges of commercial roofs and direct it to the ground. There are several types of edge drains as follows:
- Scupper drains: These are round or square protruding openings roofers make along the edge of commercial roofs to drain water away from the building, mostly feeding it to downspouts.
- Gutters: These catch water as it rolls off the roof edge and diverts it to downspouts and out the drainage system.
- Downspouts (roof drain leaders): These pipes carry water away from scuppers or gutters and direct it to the ground.
4. Materials Used in Commercial Roofing Drainage Systems
Commercial building roof drains come in different materials to solve various problems facing your drainage system. These include:
- Cast Iron: It’s the most popular drainage material with numerous advantages such as durability and quietness. Modern cast iron coatings prevent buildup of residue blocking the pipe’s flow. Unfortunately, its high cost makes it unavailable to most property owners except as a drain cover to keep out large debris.
- PVC (polyvinyl chloride): It’s a cheaper alternative to cast iron, non-toxic, abrasion-resistant, and easier to cut into shapes. While it is weaker than cast iron, it is also a cheaper alternative.
- Propylene: It’s a petroleum waste by-product with similar advantages to PVC but much less likely to burn in the event of a fire (but without the toxic smoke of PVC). Its light nature makes it unsuitable for roof drain covers or strainers, but pairing it with a cast iron drain cover or strainer can add protection without the cost of all cast iron.
- ABS (acrylonitrile butadiene styrene): It’s similar to PVC but performs poorly in the sun and is generally not receommnded for use on the roof.
At the end of the day, you should talk to your roofer about what the best choice for your roof is. The best choice depends on the size of the project, the building’s needs, and your budget.
5. Commercial Roof Drainage System Maintenance
All commercial roof drainage systems need professional roofing maintenance annually or semiannually. Roofs with a history of drainage problems or several trees nearby require more frequent inspection and cleaning.
Contact the friendly, reliable, and knowledgeable team at Texas Traditions Roofing in Georgetown, TX, if you have any doubts, concerns, or queries about your commercial building roof drains. We are a proud GAF Triple Excellence Award recipient for distinguished services in installation, consumer protection, and training excellence.