Why do Commercial Buildings have Flat Roofs

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An aerial view of a building with a flat roof.

Why do Commercial Buildings have Flat Roofs


When we think of commercial buildings, one common feature that often comes to mind is the flat roof. Unlike the pitched roofs frequently seen in residential settings, flat roofs dominate the skyline of business districts and industrial parks. But have you ever wondered why this architectural choice is so prevalent? This article delves into the intricacies of flat roofs, exploring their benefits and drawbacks, the types and materials commonly used, and why they remain a popular choice for commercial buildings.

Key Takeaways

  • Flat roofs are cost-effective, with lower initial construction costs and simplified structure, making them appealing for commercial use.
  • The horizontal surface of flat roofs facilitates easy installation of utilities and allows for vertical expansion of buildings. They offer extra usable space for various functions like solar panels, rooftop gardens, and recreational areas, optimizing commercial property investments.
  • Flat roofs feature built-up insulation and special coatings for energy efficiency, reflecting sunlight and reducing heat absorption.
  • These roofs are easier to inspect and maintain due to their accessibility, with simpler snow and rain removal processes.
  • Despite their benefits, flat roofs can have challenges like poor drainage, shorter lifespan, and increased maintenance needs compared to pitched roofs.

What is a Flat Roof?

A flat roof, as the name suggests, is a type of roofing that is level in contrast to the sloped form of a pitched roof. This flat style of roofing is predominantly found in commercial and industrial buildings.

Although it appears perfectly flat, a slight pitch is generally included in the design to allow for water drainage. Depending on the total size of the commercial roof, this pitch can be the entire surface from one side to the other or made up of a series of low-slope roofs within the total roof space.  

modern office building
You can imagine if a building like this had a pitched roof how imposing it would look and many more materials would be needed.

Types of Flat Roofs

Flat roofs can be categorized into several types, depending on the materials and construction techniques used. Some common types include:

Built-Up Roof (BUR)

Comprises multiple layers of bitumen and reinforcing fabrics.

Modified Bitumen Roofing

Uses multi-layered rolls that are usually heat-applied.

EPDM Roofing

Made from a durable rubber material.


Thermoplastic polyolefin materials that are well-suited for heat-reflective and energy-efficient roofing.

Common Materials Used

Different materials offer different benefits and drawbacks. Built-Up Roofs often use tar and gravel, which are relatively inexpensive but can be heavy. Modified Bitumen is lighter and can reflect heat better. EPDM rubber is durable and resistant to weathering, but it’s not as heat-reflective as TPO or PVC, which are often white to reflect sunlight and are more energy-efficient but can be more expensive.

skylights on an industrial roof
Most commercial buildings will make use of the light available and install skylights which are easy to do on a flat roof, this natural light saves on energy costs.

Advantages using Flat Roofing for Commercial Buildings

Flat roofs provide various advantages when it comes to commercial applications. The initial construction cost is often lower due to the simplified structure.

The horizontal surface makes it easier to install utilities like HVAC systems. Its design flexibility also allows for easy expansion vertically, should the building need to add more floors.

Space is often at a premium in commercial settings, and a flat roofing setup offers extra usable space. The roof can be utilized for various functionalities ranging from placing solar panels for energy conservation to creating a rooftop garden for environmental sustainability or even employee well-being. Maximizing the space available is always a key factor that commercial property owners look for in their investments. Furthermore, flat roofs can provide a modern aesthetic that appeals to certain businesses and customers.


Initial Cost: A primary reason is that flat roofs usually require fewer materials and labor than pitched roofs, resulting in lower initial costs. Due to commerical buildings generally being very large, the surface area saved by not using a pitched roof in big saving in materials needed. 

Maintenance: The flat surface makes it easier and safer for workers to perform maintenance tasks, which can be cheaper in the long run. All work can be done realitively descretely with no distruption to employees or customers.

Space Utilization

Rooftop Equipment: A flat roof provides an ideal space for placing HVAC units, solar panels, and other utilities, keeping the ground around the building free for other uses such as parking.

Green Roofing: Flat roofs offer the opportunity to create green roofs, these ‘living’ roofs provide additional insulation and manage stormwater runoff.

Recreational Use: The flat space can also be used for employee recreation areas, rooftop bars, or even additional retail space.

Aesthetic Versatility

Design: The simplicity of flat roofs allows for greater freedom in building design, including the possibility for extensive window placement.

Modern Look: For some, the flat roof offers a modern, clean appearance compared to more traditional pitched roofs.

roof of the building with ventilation hatchways, air conditioning, antennas, electricity
Having a large space that cannot be seen from the ground allows a area for all the less aesthically pleasing items to go that are essential for the building’s operation.

Energy Efficiency

Insulation: Many flat roofs feature built-up insulation layers that can be more energy-efficient than pitched roofs.

Cool Roof Coatings: Special coatings can be applied to reflect more sunlight and absorb less heat, resulting in lower energy costs.


Ease Of Inspection: With no slopes or angles, flat roofs are easier to walk on for inspections and repairs which need to happen at regular intervals in order to keep the building up to code and open for business.

Snow And Rain Removal: Flat surfaces are more accessible for clearing snow and rainwater, although they do require a slight pitch or efficient drainage system to prevent water accumulation. You could imagine how dangerous a large pitched roof would be if it has many feet of snow just waiting to slide off onto the sidewalk or parking lot.


Future Expansion: If the building needs to be expanded vertically, a flat roof allows for easier upward construction.

Multi-Use: They are easily adaptable for different uses and modifications like installing a new equipment or structures.

Structural Benefits

Wind Resistance: Flat roofs typically offer less wind resistance than pitched roofs, making them more stable during storms and keeping the HVAC systems better protected.


Extra Space: Depending on load-bearing capabilities, flat roofs can be used for additional storage space for things like inventory or building maintenance materials. These are not only eliminating a possible eyesore they are also more secure.

While flat roofs have numerous advantages, they also come with their own set of challenges, such as drainage issues and potentially higher maintenance costs for waterproofing systems. However, with proper design and maintenance, many of these challenges can be effectively managed

solar panels installed on a roof of a large industrial building
Flat roofs offer a big space that can be utilized for a variety of things including offsetting the building’s energy consumption by installing solar panels.

Disadvantages of Having a Flat Roof

Poor Drainage: Flat roofs are prone to water pooling, leading to potential leaks and water damage.

Shorter Lifespan: Materials commonly used for flat roofs often have a shorter lifespan compared to those used for pitched roofs.

Increased Maintenance: In general they require more frequent maintenance to manage drainage and prevent leaks.

Weight Bearing Issues: Accumulated snow or water can add extra weight to the roof, potentially causing structural problems.

Limited Insulation: They may offer fewer options for effective insulation, which can impact energy efficiency.

Durability Concerns: The materials for flat roofs may degrade faster due to greater exposure to the elements, including ultraviolet rays.

Higher Long-Term Costs: While initial costs may be lower, the expenses for regular maintenance and potential repairs can add up over time.

Design Limitations: Flat roofs may offer fewer aesthetic options compared to pitched roofs.

Heat Absorption: Some flat roofing materials can make the building hotter, increasing cooling costs.

Alternatives to Flat Roofs

While flat roofs are a popular choice for commercial buildings, other options exist. Pitched roofs, though more commonly seen in residential settings, can sometimes be used in commercial buildings where aesthetic variety is desired. A-frame roofs and dome-shaped roofs provide architectural interest but may not offer the same level of space utility as flat roofs.

So Why Do Residential Homes Have Sloped Roofing?

Since we have talked to much about commercial properties having flat roof designs, you may be now wondering why almost all residential buildings have sloped roofs. Let’s touch on these briefly so you have a full picture on all the angles roofs can take.

Benefits of sloped roofs on residential properties:

  • Deal easily with rain and snow and give less opportunity for leaks to enter.
  • Allows for a space between the living areas of the home and the outside which gives an insulation buffer.
  • Gives an area for storage which is often tight in houses as added cupboard space greatly affects the usable square footage of the home.
  • With most homes having a limited size section having a peaked roof maximizes the space available as you get more space without increasing the footprint of the house. 


As we’ve explored, the prevalence of flat roofs in commercial architecture is no mere coincidence. Their cost-effectiveness, functional versatility, and design flexibility make them an attractive option for business owners and architects alike.

However, it’s important to recognize that flat roofs are not without their challenges, particularly when it comes to drainage and maintenance. Alternatives do exist, but they often don’t offer the same advantages in terms of space utilization and expandability.

Ultimately, the choice of roofing is a complex decision that involves weighing multiple factors, from initial construction costs to long-term maintenance requirements. Understanding these elements can help in making an informed choice. It is best to talk to a commercial roofing contractor and layout your requirements and budget for them to give useful advice on the best roofing solution for you.

Frequently Asked Questions

Why do commercial buildings often have flat roofs?

Flat roofs are cost-effective, provide extra space for HVAC systems, and are easier to inspect and maintain than pitched roofs. They also allow for more flexible architectural designs in commercial construction.

Can flat roofs handle heavy rain and snow?

Yes, modern flat roofs are engineered to handle heavy rain and snow. They typically have a slight incline and drainage systems to prevent water accumulation and potential damage.

Is it more expensive to maintain a flat roof on a commercial building?

Maintenance costs can be higher due to the need for regular inspections and repairs, especially in areas with extreme weather conditions. However, the initial installation is often more cost-effective.

Can solar panels be installed on flat roofs?

Absolutely. Flat roofs are ideal for solar panel installation due to the ease of mounting and the ability to orient panels for optimal sun exposure. This makes them a popular choice for energy-efficient buildings.

A worker is working on a metal roof.

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