Flat roofs cost less than traditional roof types and can create space for an outdoor patio or rooftop garden. However, there are a few types to choose from when finding the right one for your home. We’ll cover three popular flat roof types, how they’re made, and their pros and cons to help you make the best decision for your space.
Understanding Flat Roof Systems
Flat roof systems aren’t actually completely flat; they have a slight pitch to allow for water drainage. They’re popular in areas with low rainfall and on buildings where roof space is used for mechanical equipment or recreational purposes.
The three main types of flat roofs, each known by an acronym, have unique characteristics suited to different needs and budgets.
Built-Up Roof (BUR)
Built-up roofs, often referred to as BUR, have been a staple in the roofing industry for over a century. These roofs are known for their ability to withstand harsh weather conditions.
A BUR system consists of alternating layers of bitumen (better known as asphalt) and reinforcing fabric, creating a durable, waterproof membrane. Layers are alternated with hot tar and stabilized by a layer of smooth stone. Modern BUR systems may use more advanced materials like fiberglass membranes instead of traditional tar paper.
Advantages of Built-Up Roofs
- Excellent fire resistance due to the gravel top layer
- Attractive appearance for buildings with windows or decks overlooking the roof
- Typically the cheapest option among flat roof types
- Proven track record of durability and longevity
Drawbacks of Built-Up Roofs
- Significantly heavier than other flat roof options, sometimes requiring additional structural support
- Installation can be messy and smelly, making it less suitable for occupied buildings
- Difficult to identify the source of leaks when they occur
Modified Bitumen Roof (MBR)
A modified bitumen roof is a type of roofing system made from asphalt that has been modified with certain chemicals to enhance its performance. It’s durable and waterproof like traditional asphalt, but stronger and more flexible like modern synthetic materials.
Like built-up roofing, modified bitumen roofs consist of multiple layers. These layers include a base sheet, one or more ply sheets, and a cap sheet. Modified bitumen roofs are lighter and easier to install than bulit-up roofing and offer superior flexibility and thermal resistance.
Advantages of Modified Bitumen Roofing
- Easier installation compared to BUR, including options for peel-and-stick application
- Reflective surface options that can help reduce energy costs
- Good resistance to foot traffic and impacts
- Moderate cost, typically falling between BUR and EPDM options
Drawbacks of Modified Bitumen Roofs
- Torch-down application methods can pose a fire hazard during installation
- Less scuff- and tear-resistant than rubber membrane roofs
- May require more frequent maintenance than other flat roof types
Rubber Membrane Roof (EPDM)
EPDM (ethylene propylene diene monomer) roofing is a popular single-ply roofing option known for being durable and easy to install. It consists of a synthetic rubber compound engineered to resist damage from sunlight and weather extremes. It’s typically available in large sheets, reducing the number of seams on the roof.
Advantages of EPDM Roofing
- Lightweight material that doesn’t require additional structural support
- Highly resistant to scuffs, tears, and punctures
- Easy to repair if damage occurs
- Long lifespan, often lasting 20-30 years with proper maintenance
- Suitable for DIY installation
Drawbacks of EPDM Roofing
- Standard black material absorbs heat, potentially increasing cooling costs
- More expensive than BUR or modified bitumen options
- Can be punctured by sharp objects, requiring careful handling during installation and maintenance
Comparing Flat Roof Costs
Flat roofing costs vary significantly depending on the material. Prices generally range from $4–$13 per square foot.* BUR tends to be the cheapest, followed by modified bitumen, with EPDM typically being the most expensive. However, you should also consider the long-term value of your selected material, including durability, maintenance requirements, and potential energy savings.
*Cost figures in this article were sourced from HomeAdvisor and internal data.
Lifespan and Warranty Considerations for Flat Roofs
Flat roofs usually come with a 10- to 20-year warranty but can last up to 25 years with proper installation and maintenance. EPDM roofs often have the longest lifespan at up to 50 years, followed by BUR and modified bitumen at 20–30 years. Before choosing a roofing material, take time to understand what the warranty covers and for how long, as well as any maintenance requirements to keep the warranty valid.
Maintenance Requirements for Different Flat Roof Types
Regular maintenance is key to helping your roof last. Apart from regularly removing debris and vegetation, which is recommended for all three types, each flat roof has specific maintenance needs to keep it at peak performance. Here are some steps to take for each materials.
BUR Maintenance
- Inspect gravel coverage and reapply if necessary
- Check for and repairing any cracks or blisters
Modified Bitumen Maintenance
- Periodically look for seam separation or surface degradation
- Apply reflective coatings as needed to maintain energy efficiency
EPDM Maintenance
- Inspect seams and flashing for potential weak points
- Promptly repair any punctures or tears in the membrane
Read more: Some Commonsense Rules for Maintaining a Flat Roof
Climate Considerations When Choosing a Flat Roof
Your local climate greatly impacts which flat roof type is best for your home. Here’s what we recommend:
- In hot climates, reflective EPDM or modified bitumen with light-colored surfaces may be preferable to reduce heat absorption.
- For areas with heavy rainfall or snow, BUR systems offer excellent water resistance with their multiple layers.
- In regions with extreme temperature fluctuations, EPDM’s flexibility can help prevent cracking and splitting.
Professional Flat Roof Installation vs. DIY
While some flat roofing projects can be DIY-friendly, particularly if you’re installing peel-and-stick modified bitumen or an EPDM system, we recommend professional installation for most roofs. Roofing pros have the experience, tools, and knowledge to ensure proper installation, which is crucial for the roof’s performance and longevity. You can consider DIY installation for smaller projects or repairs, but we recommend leaving it to the experts to ensure your flat roof is built safely.
