Why Are Flat Roofs Common on Commercial Buildings?

by | Nov 28, 2022 | Equipment Considerations, Planning and Budgeting

Many building owners ask, “Why do they even make a flat roof?” From their perspective, if the roof on their house is sloped, why does their warehouse or office need a flat roof?

Commercial flat roof building owners who have had chronic problems with their roofs blame the whole idea of a flat roof for their issues. They lament their roof and wonder why anyone would want or build one.

The answer is, when flat roofs are properly designed and installed, they end up being the lowest-cost roof system over the life cycle of a building – a life cycle that can last as long as 100 years. That is one big and compelling reason why flat roofs are so popular amongst commercial building owners.

Save Money With a Flat Roof

You may be thinking, “How can a flat roof be the lowest cost roof over time? Aren’t they a maintenance nightmare?”

The answer is “no”. This cost analysis includes both the cost to build and the cost to maintain. And the reason flat roofs come out ahead of pitched roofs is that it is far less costly to build a roof pitched at 0.25 inches per foot than it is a 5-inch-per-foot pitched roof.

Think of, for example, a building with a 300 by 300 footprint. If you were to pitch the roof on that building like the roof on your house, it would be pitched at a 5:12 pitch. You would need an additional 62.5 feet of roofing materials in the center of the building to accommodate that roof. A flat roof that is pitched in the middle at a 0.25:12 pitch, would only need 6.25 feet of rise in the center. This smaller pitch is much easier to build (not much more than building a regular floor) and it cuts down on wasted space. Just think about having to build an extra six stories of height into your building, just to shed the water off the roof!

Additional Benefits

Building owners can not only save money with a low-slope roof, they can also stretch the value derive from occupying one. What do I mean by that? A flat roof is a perfect, low-cost and esthetically pleasing place to store and service unsightly materials like building air conditioners and solar panels. It is also a great place for a rooftop garden, patio, and/or deck, a benefit that can be enjoyed by you, your employees, and your customers.

Flat Roofs Are Not Flat

Even after being presented with these facts people still bring up the maintenance aspect of a flat roof. Remember, it must be properly designed and installed. Let’s put aside proper installation, because regardless of the pitch of the roof, if it’s not installed correctly it will be a maintenance nightmare. Proper design is equally important.

Despite the name, a flat roof is not flat. In fact, the industry does not say “flat roof” they say “low-slope roof” which is more accurate because all properly designed roofs have some pitch. Most commonly a “flat roof” has a 0.25 inch per foot slope.

I’ve seen many owners with chronic roof problems whose roofs are pitched at 0.00 inches per foot of slope– yes, dead flat! This is a true maintenance nightmare because the roof has chronic ponding water which will infiltrate the building. Many buildings built in the 1960s and ‘70s were built this way, and it is something to avoid at all costs.


It makes good economic sense for commercial and industrial buildings to be constructed with near-flat or low-slope roofs. It keeps construction and maintenance costs down and opens up options for additional use. These are main the reasons flat roofs are so popular with commercial and industrial building owners and why you see so many of them in your travels.

Expert Advice

Whether you’re a beginner, need advanced information about flat roofing topics, or a refresher,  this is where you can learn everything you need to know about commercial and industrial flat roofing.

Contact us for more information or pricing.




Jared Van Vranken is Vice President and lead estimator at Flat Roof Solutions in Malvern, PA. Jared has directed the installation, repair, recovery, and replacement of commercial flat roofs for more than a decade at Flat Roof Solutions. He guides clients in selecting the best roofing materials for their needs and budget.

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