What a Flat Roof Is Called: Types and Common Names

The term “flat roof” often prompts questions about its types, materials, and industry names. This article explains what a flat roof is called, outlines the most common names and systems, and provides practical details for homeowners, contractors, and real estate professionals. Readers will learn the distinctions between flat roof types, their benefits, drawbacks, and typical uses.

Common Name	Also Called	Typical Material
Built-Up Roof (BUR)	Tar and Gravel	Asphalt Layers, Gravel
Modified Bitumen	Mod-Bit	Asphalt Sheets with Reinforcement
EPDM	Rubber Roof	Synthetic Rubber Membrane
TPO	Thermoplastic Olefin	Single-Ply Thermoplastic Membrane
PVC	Polyvinyl Chloride	Single-Ply Plastic Membrane

What Defines A Flat Roof

A flat roof is typically defined as a roof with a low slope, generally less than 3:12 (meaning three inches of rise for every 12 inches of run). Despite the name, most “flat” roofs have a slight pitch to allow drainage. Flat roofs are common on commercial buildings, modern residential homes, and some extensions or garages.

Common Names For Flat Roofs

Flat roofs are referenced by material and system type more often than by a single universal name. Common industry names include Built-Up Roof (BUR), Modified Bitumen, EPDM, TPO, and PVC. Each name reflects a specific construction method or membrane material.

Built-Up Roof (BUR) — “Tar And Gravel”

Built-Up Roofs, often called “tar and gravel,” consist of alternating layers of felts and hot asphalt or coal-tar pitch, finished with a layer of gravel. BUR has been used for decades and is known for durability and UV protection from the gravel cap.

Modified Bitumen — “Mod-Bit”

Modified bitumen roofing uses asphalt modified with polymers and reinforced with polyester or fiberglass. It is usually installed in sheets and can be applied with a torch, hot mop, or cold adhesives. Mod-bit offers flexibility, good UV resistance, and is a common retrofit choice for older BUR roofs.

EPDM — “Rubber Roof”

EPDM (ethylene propylene diene monomer) is a synthetic rubber membrane widely used for low-slope buildings. It typically comes in large sheets that are mechanically fastened, fully adhered, or ballasted. EPDM is prized for its weather resistance, ease of repair, and cost-effectiveness.

TPO And PVC — Thermoplastic Single-Ply Membranes

TPO (thermoplastic olefin) and PVC (polyvinyl chloride) are single-ply thermoplastic membranes. Both are heat-weldable at seams, creating strong, watertight bonds. TPO is known for energy efficiency and reflective white options; PVC is valued for chemical resistance and long-term performance.

Green Roofs And Inverted (Protected Membrane) Roofs

Some flat roofs are called “green roofs” when vegetative layers are installed above the waterproof membrane. Inverted or protected membrane roofs place insulation above the waterproofing layer, often with ballast or pavers on top. These systems alter standard naming conventions due to added components and functions.

Metal Flat Roofs And Low-Slope Metal Options

Although metal roofs are often associated with steep slopes, standing seam metal panels and certain metal systems can be installed on low slopes and are sometimes referred to as flat or low-slope metal roofs. Metal provides durability and a distinct aesthetic for modern flat-roofed buildings.

How Roofing Professionals Refer To Flat Roofs

Roofers and architects typically specify the system rather than calling something simply a “flat roof.” Specifications include membrane type, insulation, attachment method, and finish. For example, a professional will say “fully-adhered TPO single-ply” rather than just “flat roof.”

Advantages Of Flat Roofs

Flat roofs offer usable space for HVAC equipment, solar panels, terraces, or green roofs. They are usually less expensive to construct per square foot and easier to access for maintenance. These practical advantages explain their popularity on commercial and contemporary residential buildings.

Common Disadvantages And Maintenance Concerns

Flat roofs require careful attention to drainage and flashing details; standing water can accelerate membrane degradation. Regular inspections, cleaning of drains, and timely repairs are essential. Most leaks originate at penetrations, edges, and seams rather than through the field membrane itself.

When To Use Each Flat Roof Type

Choosing a flat roof system depends on budget, climate, roof traffic, and desired lifespan. EPDM and TPO are common cost-effective choices; BUR and modified bitumen are chosen for longevity and proven performance; PVC is selected for chemical resistance in industrial settings.

Cost Considerations And Lifespan

Initial costs vary: EPDM tends to be among the least expensive; TPO and PVC can be mid-range; BUR and high-quality modified bitumen can be more expensive. Lifespans range from 10–30+ years depending on materials, installation quality, and maintenance. Energy efficiency, warranties, and long-term maintenance costs affect lifecycle value more than initial price alone.

Energy Efficiency And Reflective Options

White or reflective membranes like TPO and PVC can significantly reduce cooling loads in warm climates. Cool roof coatings are also available for BUR and modified bitumen. Reflective flat roof options help lower utility bills and may qualify for incentives or utility rebates.

Inspection, Repair, And Replacement Tips

Flat roofs should be inspected biannually and after major storms. Key checks include membrane integrity, seam condition, drain functionality, and roof-mounted equipment flashings. Small punctures and seam failures can often be repaired, but extensive oxidation or multiple wet insulation areas usually indicate replacement is needed.

Regulations, Codes, And Warranties

Building codes influence flat roof design for drainage slope, insulation (R-value), and fire rating. Manufacturer warranties vary by membrane and installation method; some require certified installers. Understanding local codes and warranty terms helps avoid costly compliance or coverage issues.

How To Talk About Flat Roofs In Real Estate Listings

For listings and descriptions, referencing the specific system adds buyer confidence—for example, “TPO Low-Slope Roof With 10-Year Warranty.” Clarity about roof age, recent repairs, and material type reduces surprises during inspections.

Key Takeaways For Homeowners And Property Managers

Knowing what a flat roof is called helps in decision-making and communication. Identifying whether the roof is BUR, modified bitumen, EPDM, TPO, or PVC clarifies expected performance, maintenance, and replacement costs. Regular inspections and proper drainage management extend the service life of any flat roof system.

Resources For Further Reading

• NRCA (National Roofing Contractors Association) offers technical guidance on low-slope roofing systems.
• EPA and local building codes provide information about cool roofs and insulation requirements.
• Manufacturer guides for EPDM, TPO, and PVC detail installation and warranty conditions.

For specific project planning, consult a licensed roofing contractor or building envelope specialist to evaluate existing conditions and recommend the best flat roof system for the building’s needs.