What is a Flat Roof?

A flat roof is a roof with a slight slope—typically 1–10 degrees—that allows for water drainage while appearing level. Commonly used on garages, extensions, and commercial buildings, flat roofs are usually covered in waterproof membranes like EPDM or GRP. They offer a modern look, ease of access, and practical use of space.

Flat roofs have evolved significantly thanks to modern materials and innovative technologies. Whether you’re planning a residential build or a commercial project, flat roofs have become a popular option in the UK — and with good reason. But what makes them so effective? What exactly is a flat roof? In this blog, we unpack everything you need to know about flat roofs.

What is a Flat Roof?

Despite the name, flat roofs aren’t completely flat. Instead, they have a slight pitch — typically between 1–10 degrees — to allow water drainage. This design is covered with a waterproof membrane and commonly found on extensions, garages, carports, and outbuildings. You’ll often find them used in both residential and commercial applications due to their versatility.

Types of Flat Roofs

Different flat roofing materials offer varying lifespans, durability, and installation complexity. Below are the most common types used in the UK:

Built-Up Roofing (BUR)

Also known as tar and gravel roofs, BUR systems have been in use for over a century. These roofs consist of multiple layers of tar and gravel and typically last between 10–15 years. They offer good waterproofing, fire resistance, and insulation, though the gravel layer often needs periodic replacement.

Concrete Roofs

Concrete roofs are layered systems built with cement, sand, and water, often topped with vapour barriers and insulation. These are weather-resistant, fireproof, low maintenance, and can last up to 50 years.

EPDM (Ethylene Propylene Diene Monomer)

This synthetic rubber membrane is a budget-friendly option and widely used in commercial flat roofing. It’s lightweight, recyclable, fireproof, and water-resistant with a potential lifespan of 10–50 years. Learn more about EPDM and compare with other materials in our guide to the best flat roofing materials.

GRP (Glass Reinforced Polyester)

Made of fibreglass and polyester, GRP is a single-ply laminate that’s easy to install and maintain. Best used in low foot traffic areas, it lasts between 25–50 years and is both economical and durable.

Metal Roofs

Flat metal roofs are constructed using fastened sheets of steel, zinc, aluminium, or copper. These materials offer a lifespan of up to 100 years and are recyclable, customisable, and weather-resistant. Read more about different types of metal roofing.

Modified Bitumen Systems (MBS)

This single-ply material combines fibreglass and tar and is well-suited for sheds and small buildings. It can be coated with elastomeric paint for UV protection and generally lasts 15–30 years.

PVC (Polyvinyl Chloride)

PVC is a flexible, thermoplastic waterproof membrane. Heat-welded at the seams, it’s resistant to chemicals, fire, wind, and UV rays, with a lifespan of around 20–30 years.

Advantages of Flat Roofs

Cost-Effective Construction

Flat roofs are more economical than pitched roofs — not just in installation but also in repairs and extensions. Compare with flat and pitched roof extensions.

Additional Storage Space

Whether you want to add solar panels, store ladders, or install a satellite dish, a flat roof gives you that added outdoor space without ruining your property’s aesthetic.

Ease of Access

Routine maintenance like clearing debris or inspecting gutters is simpler on flat surfaces. This accessibility makes them especially practical for DIY enthusiasts. Check our roof maintenance checklist.

Long Lifespan

Modern materials like EPDM or GRP offer lifespans of up to 50 years and beyond. They’re also more durable and water-resistant than older materials like traditional felt.

Multi-Use Space

From a roof garden to a private lounge space, the usability of a flat roof is a major perk for urban homes.