The terms “flat roof” and “commercial roof” are usually synonymous. That’s because most commercial roofs are flat instead of sloped, which is common for residential roofs. There are a few reasons why flat roofs are typically better suited for commercial buildings.
One of the main reasons most commercial roofs are flat is the additional structural cost it would take to make them sloped. On a large building (think a mall or big box store) a sloped roof would be cost prohibitive because of the amount of material it would take to construct the roof support assembly. A sloped roof on a large building might also require several peaks and valleys, which would add to the complexity and cost.
Commercial buildings often have equipment, like HVAC units or other machinery, on the roof because it’s a secure space that’s typically not needed for other building functions and distanced from where the equipment might present safety or noise problems. Although a sloped-roof installation for HVAC equipment might be doable, it’s probably not practical from a cost and ease-of-maintenance standpoint.
Flat roofs can be better for rooftop solar systems, because they provide more options for positioning panels to take advantage of the sun’s track across the sky. Plus, installation and maintenance of this equipment are safer on a flat roof.
Of course, a “flat roof” isn’t absolutely flat. All roofs have some slope to them to allow for drainage. However, over time, a roof can lose its slope in places due to the building settling or flattening caused by heavy rooftop equipment or ponding water. In these cases, a roofing contractor may install what are called “crickets” or “saddles” that are placed in critical areas to provide slope toward a drainage area. They are then integrated with the roofing system by covering them with compatible membrane.
If you are considering a new roofing system for your flat commercial facility, make sure the contractor evaluates the slope of the entire rooftop to ensure proper drainage. If adjustments need to be made with crickets, it’s obviously best to do them prior to the new membrane installation.