flat roof apartment

Why Do Most Apartment Buildings Have Flat Roofs?

As you look across the Denver skyline, you see a lot of different building types. 

Most of the taller ones are commercial office buildings. Then, there are few parking lot structures. Before long, you might start to notice that there’s a theme with most of the apartment buildings you see dotting the urban landscape here in Colorado. 

That theme is flat roofs. They’re everywhere in our state, and they’re especially popular in the design and construction of apartment buildings. This might have you wondering, “Why are so many apartment buildings flat-roofed?”. 

As your resident roofing experts here in Colorado, we thought we’d tackle this question and provide a definitive answer. 

Flat Roofs Aren’t Really Flat

When most people think of the word ‘flat’, they think of something that has zero slope to it. However, virtually all flat roofs in Colorado and elsewhere are simply referred to as being flat, even though they really aren’t. 

flat roof

You see, if a roof was perfectly flat, rainfall and melted snow would pool and remain in place. This would cause problems for the roofing system, as standing water is notorious for causing damage over time. 

So, instead of designing apartment buildings with truly flat roofs, architects and engineers actually integrate a small slope into the roof structure. This slope might be tiny (say, ¼-inch of slope for every foot of roofing), but it’s all that’s needed to effectively allow water to drain away from the building as it should. 

The Cost Factor

The most significant reason why apartment buildings have flat roofs has to do with the cost of erecting a building with a flat roof versus erecting a similarly sized building with a conventional, sloped roof. 

Flat roofs are much less expensive to build. Not only is there less framing material used in the construction of a flat roof, but there are also no shingles, tiles, or shake necessary to channel water to the gutters and downspouts. Furthermore, because less material is needed to complete a flat roof, less labor is required to complete construction. This results in a significant cost savings for the property owner. 

Even though flat roofs don’t need to be shingled like conventional roofs do, they still need to be protected from water leaks and UV exposure. Here in Colorado, the most common methods for doing this include using one or more of the following commercial roofing materials: 

  • Built-Up Roofing (BUR) Membrane
  • Metal Roofing (including aluminum, copper, tin, or some other alloy)
  • Modified Bitumen Roofing Material
  • Thermoset (EPDM) Roof Membrane
  • PVC Roof Membrane
  • TPO Roof Membrane

In addition to these common flat roof solutions, some property owners are opting for ‘living roofs’ or ‘green roofs’, where trees, shrubs, and other vegetation are planted for the purpose of absorbing UV energy, improving air quality, and enhancing aesthetics. 

Flat Roofs Add Usable Space

Here’s another reason why apartment buildings make use of flat roofs instead of sloped ones: flat roofs allow for the installation and operation of HVAC equipment like vents, chillers, furnaces, and more. Also, storage sheds or utility closets can often be installed on flat roots, whereas this wouldn’t be possible in a sloped roof scenario. 

Moving to the interior of a building, we find that a flat-roofed apartment building is going to allow for more efficient use of more square footage for residents. If the roof is sloped, there is almost always going to be unused attic or crawl space that isn’t going to be as useful for the property owner or the tenants below. 

Flat Roofs are Easier and Cheaper to Maintain

If a heavy hailstorm hits Colorado and roofs become damaged, flat roofs are going to be easier and cheaper to repair, square foot-for-square foot, compared with conventional, sloped roofs. 

For example, repairing a punctured PVC roof membrane on a flat roof might only require a few hours of labor and a few patches of bonded PVC membrane. However, repairing equitable damage on a sloped roof would likely require project planning over days to ensure the right materials were on hand, the correct safety precautions are taken, and a large enough crew is available to do the job right. 

And then, there’s the cost factor again. Repairing a flat roof is going to cost a fraction of what it would cost to perform a similar repair on a sloped roof. 

Have more questions about roofs, roof repair, or roof replacement in Colorado? We’d love to help!

Contact A-to-Z Roofing & Exteriors today!

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