While gable roofs are more traditional, flat roofs are a common feature for commercial buildings and growing increasingly popular in modern residential designs. While they may appear simple, flat roofs require careful consideration when it comes to materials and installation.
This article explores the three main types of flat roof materials. We’ll delve into how they’re made, the advantages and drawbacks of each, and other crucial factors to help you make the right decision for your roofing project.
Understanding Flat Roof Systems
Flat roof systems are not actually completely flat but 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, offer 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 robust construction and 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
Built-up roofs offer several benefits that have made them popular:
- Excellent fire resistance due to the gravel top layer
- Attractive appearance for buildings with windows or decks overlooking the roof
- Typically the most cost-effective option among flat roof types
- Proven track record of durability and longevity
Drawbacks of Built-Up Roofs
Despite their advantages, BUR systems do have some limitations:
- Significantly heavier than other flat roof options, sometimes requiring additional structural support
- Installation can be messy and odorous, 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 combines the durability and waterproofing characteristics of traditional asphalt with the flexibility and strength of 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. But modified bitumen roofs are lighter and easier to install than bulit-up roofing and offer superior flexibility and resistance to thermal movement.
Advantages of Modified Bitumen Roofing
Modified bitumen roofs offer several advantages:
- Easier installation compared to BUR, with some systems offering 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
Some drawbacks of modified bitumen roofing include:
- Torch-down application methods can pose a fire hazard during installation
- Less scuff- and tear-resistant compared to 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 its durability and ease of installation. 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
EPDM roofing has numerous benefits:
- 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, making it a homeowner-friendly option
Drawbacks of EPDM Roofing
Some drawbacks of EPDM roofing include:
- Standard black material absorbs heat, potentially increasing cooling costs
- More expensive than BUR or modified bitumen options
- Can be punctured by sharp objects, which means careful handling during installation and maintenance
Comparing Costs
The cost of flat roofing materials can vary significantly depending on which you choose. Generally, prices range from $4 to $13 per square foot. BUR tends to be the most economical option, followed by modified bitumen, with EPDM typically being the most expensive. However, long-term costs should also consider durability, maintenance requirements, and potential energy savings.
Lifespan and Warranty Considerations for Flat Roofs
Flat roofs usually come with a 10- to 20-year warranty, but with proper installation and maintenance, can last up to 25 years. EPDM roofs often have the longest lifespan, followed by BUR and modified bitumen. When considering warranty options, it’s important to understand what they cover 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 for extending the life of any flat roof system. Apart from regularly removing debris and vegetation, which is recommended for all three, each roof has specific maintenance needs to keep it at peak performance.
BUR Maintenance
- Inspection of gravel coverage and reapplication, if necessary
- Checking for and repairing any cracks or blisters
Modified Bitumen Maintenance
- Periodic inspections for seam separation or surface degradation
- Application of reflective coatings as needed to maintain energy efficiency
EPDM Maintenance
- Inspection of seams and flashing for potential weak points
- Prompt repair of any punctures or tears in the membrane
Climate Considerations When Choosing a Flat Roof
Your local climate plays a significant role in determining the best flat roof type for your home:
- 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 Installation vs. DIY: What You Need To Know
While some flat roofing projects can be DIY-friendly, particularly with peel-and-stick modified bitumen or EPDM systems, we recommend getting a professional to install most roofs. Skilled 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 to ensure your roof is built safely and strongly, complete roof replacements are best left to the experts.
Our Conclusion
Choosing the right flat roof system depends on various factors, including budget, climate, building structure, and long-term maintenance considerations. Built-up roofs offer traditional durability and cost-effectiveness but come with installation challenges. Modified Bitumen provides a balance of modern materials and ease of installation, while EPDM offers superior flexibility and longevity, albeit at a higher initial cost.
Ultimately, the best flat roof for your project will depend on your specific needs and circumstances. Consider talking with a roofing professional to assess your building’s requirements to help you make an informed decision. Whichever system you choose, proper installation and regular maintenance are key to ensuring your flat roof provides reliable protection for years to come.