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Why Are Commercial Roofs Typically Flat?

February 28, 2017


If you look at commercial roofs throughout Nevada (and the rest of the country, for that matter), you will notice that most of them are flat.


Why are most schools, grocery stores, factories, hospitals and other industrial buildings designed with flat roofs? Why aren’t they sloped or peaked like most residential roofs?


If you guessed that cost is the reason, you have only part of the answer.


Flat Commercial Roofs Are Cost-Effective


Yes, budget is a big concern in the design and construction of commercial buildings, particularly since these structures typically have large footprints.


Simply put, flat commercial roofs are cheaper to install because they require fewer materials. Adding peaks and valleys would necessitate a more complex design and result in extra framing costs.


Just like your home, retail and industrial buildings require effective drainage systems to facilitate the runoff of rainwater and melting snow. This increases the cost of the roof, but in most cases, installing a flat roof with a drainage system is still less expensive than any other design.


But commercial buildings don’t have perfectly flat roofs. They may look flat from the ground, but they have a very slight slope (about 2 percent). This prevents water and snow from accumulating, which would add weight to the roof and potentially cause damage.


Steep Slopes Aren’t Practical for Most Commercial Roofing


Building size matters when it comes to designing and constructing a commercial roof.


To design a sloped roof for a large building, the peak would need to be extremely tall or feature multiple peaks and valleys. Neither of those options is practical in most cases.


In addition, building codes in many cities and municipalities impose height restrictions for commercial structures.


Retail and industrial facilities must maximize their square footage, so it doesn’t make sense to invest in expensive sloped roofing. That money is better spent creating usable square footage.


Finally, a peaked roof on a large commercial building is usually unacceptable from an aesthetic perspective. Imagine how strange a familiar “big box” store would look with a tall, sloping roof!


Commercial Roofs Require Space for Equipment


Large commercial buildings require industrial heating and cooling equipment. Mounting this equipment outdoors at ground level is not typically allowed by code, and it can pose a variety of safety and security challenges. While the machinery can sometimes be tucked away in a basement or storage room, that takes up valuable indoor space and may also pose safety, noise or comfort issues.


Flat roofs are the perfect solution, because they provide a secure and remote location for air conditioners, heaters and other types of industrial machinery. Installing these fixtures on a rooftop poses some risks, however, as it leaves the machinery exposed to the elements. Despite this, commercial roof space is typically the location of choice for large equipment.