3 Types of Flat Roofs
New flat roofing options are appearing. They wear better than older materials, but they cost more, too.
July 2023
When choosing roofing materials for a flat roof, it’s essential to consider factors such as durability, waterproofing, and energy efficiency. Here are some common and suitable options for flat roofs.
Built-Up Roofing (BUR)
Also known as tar and gravel roofs, BUR consists of multiple layers of asphalt and roofing felt or fiberglass. It’s a traditional and time-tested option for flat roofs, providing excellent waterproofing and UV protection. The traditional hot-tar-and-gravel roof is built from three or more plies of waterproof material alternated with hot tar and ballasted by a layer of smooth river stone. Once made of tar paper, these types of roofs gradually are using more-advanced materials such as fiberglass membranes.
Pros
- Gravel is an excellent fire retardant.
- Attractive for windows and decks that overlook the roof.
- It’s the cheapest of the four roof varieties.
Cons
- Very heavy.
- Joists sometimes have to be strengthened.
- Smelly and messy to install.
- Installation is not recommended for occupied homes.
- It’s not a DIY installation job, and it is hard to find the source of leaks.
- Gravel can clog gutters and scuppers.
BUR roofs typically last about 20 to 30 years. However, regular inspections and maintenance are required to maximize the lifespan of a built-up roof.
Modified Bitumen Roofing
This roofing material is an evolution of BUR and comes in sheets or rolls. It’s made from asphalt and reinforced with modifiers such as rubber or plastic, giving it added flexibility and strength. Modified bitumen roofs are easier to install than BUR and offer good waterproofing properties. A single-ply rolled roof similar to ice-and-water shield, but impregnated with a mineral-based wear surface. Torch-down systems involve heating the adhesive as the material is unrolled. Newer peel-and-stick systems are safer and easier. 
Pros
- Peel-and-stick material can be installed by homeowners.
- Its light-colored mineral surface reflects heat and cuts energy bills.
- Its price is in the middle of the pack.
Cons
- Torch-down application is a fire hazard, and not recommended for occupied buildings.
- It’s not as scuff- or tear-resistant as rubber-membrane roofs (see the next item).
Modified bitumen roofing systems have a lifespan of about 20 years. It’s important to note that these roofing systems require very little maintenance, and with proper cleaning and attention to any necessary repairs, modified bitumen roofs can actually last for much longer.
Rubber Membrane Roof
EPDM (short for ethylene propylene diene monomer) is a true rubber. The durable single-ply membrane material resembles an inner tube, but it’s engineered to resist damage from sunlight. EPDM can be mechanically anchored with fasteners, ballasted with stone, or glued. 
Pros
- Homeowner-friendly installation.
- The material’s relatively light yet highly resistant to scuffs and tears.
- Leaks are easy to patch.
Cons
- The standard black material absorbs heat, and light-colored coatings (recommended in warm climates) add 30% or more to the cost. Even the black version, though, costs more than BUR or modified bitumen.
- It’s also more vulnerable to punctures than other choices.
A well-installed rubber roof is incredibly durable, lasting between 40 and 50 years if properly maintained. Of course, rubber roofs will last much longer if installed with proper drainage in mind.
When selecting the appropriate roofing material, consider the climate in your area, building codes and regulations, budget constraints, and the expertise of your roofing contractor. Regular maintenance and inspections are vital to ensuring the longevity and performance of your flat roof.
Alexander, M. (n.d.). 3 Types of Flat Roofs. This Old House. Retrieved July 28, 2023, from https://www.thisoldhouse.com/roofing/21015399/3-flat-roof-types?fbclid=IwAR274sQqMPXDiULEfHwMM920OJ_eWHMJV9FPy-oZa0St7iIgYHBr5ZeWVj4