What are the three types of flat roofs?

The three main types of flat roofs used on UK homes are felt (torch-on or built-up), EPDM rubber, and GRP fibreglass. Each has different characteristics, costs, and lifespans. Knowing the differences helps you choose the right system for your project or understand what you already have on your property.

Felt Flat Roofing: The Traditional Option

Felt flat roofing, sometimes called built-up felt or torch-on felt, has been used on UK homes for decades. The torch-on version involves heating modified bitumen sheets and bonding them to the roof deck in two or three layers, creating a waterproof membrane. It is the cheapest system to install and widely available from most roofing contractors.

The drawback is durability. Felt flat roofs typically last 10 to 20 years, with lifespan affected significantly by sun exposure and temperature cycling. Once the felt begins to crack, blister, or split at seams, water ingress follows quickly. Regular inspections are essential for felt roofs, particularly on south-facing sections.

EPDM Rubber Flat Roofing: Best Long-Term Value

EPDM (Ethylene Propylene Diene Monomer) is a synthetic rubber membrane that has become the dominant flat roofing material for domestic properties in the UK over the past two decades. It is installed as a single large sheet, bonded to the roof deck and trimmed to shape. The single-sheet approach eliminates most seam-related failure points.

EPDM handles temperature extremes, UV exposure, and building movement far better than felt. A quality installation should last 40 to 50 years. It is slightly more expensive than felt to install but significantly cheaper over its lifetime. Most professional flat roofing contractors now consider EPDM the standard choice for domestic extensions and garages.

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GRP Fibreglass Flat Roofing: The Rigid Option

GRP (Glass Reinforced Plastic) creates a completely rigid, seamless fibreglass surface. The system involves applying layers of fibreglass matting saturated with resin, which cures to form a hard, watertight shell. It is the most impact-resistant of the three main systems and handles foot traffic well, making it suitable for roof terraces and balconies.

GRP is typically the most expensive of the three to install and requires precise application conditions including temperature and humidity. It can be prone to cracking if building movement is significant, which makes it less suitable for larger roof spans. For smaller, rigid structures such as extensions and porches it is an excellent choice.

System	Lifespan	Walkable?	Best For
Torch-on felt	10 to 20 years	No	Budget-led projects
EPDM rubber	40 to 50 years	Occasional traffic only	Most domestic flat roofs
GRP fibreglass	25 to 40 years	Yes	Roof terraces, rigid structures

Which Is Best, EPDM or GRP?

For most domestic flat roofs on extensions and garages, EPDM is the better choice. It is more flexible, handles building movement better, and lasts longer with lower maintenance. For a roof terrace or any surface that needs to handle regular foot traffic, GRP is the stronger option due to its rigidity and harder surface.

Both are significantly better than traditional felt. The choice ultimately comes down to the application. Discuss your specific situation with your contractor, who can advise which system suits your roof’s size, structural characteristics, and intended use.

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Which Is Better, EPDM or PVC Flat Roof?

PVC membrane roofing is more commonly used on commercial flat roofs but is occasionally specified for domestic work. It is generally more expensive than EPDM and performs similarly in terms of longevity, though PVC can become brittle over time, particularly in cold climates.

For domestic applications in the UK, EPDM is the more widely used and tested choice. PVC may be worth considering for specific commercial-style applications, but for a standard house extension, garage, or outhouse, EPDM is the more straightforward and cost-effective choice.

Felt, EPDM, and GRP are the three flat roof systems you are most likely to encounter on a UK home. Each has its place, but for most new domestic flat roof work, EPDM offers the best combination of performance, durability, and long-term cost.

Frequently Asked Questions

The three main types are torch-on felt, EPDM rubber, and GRP fibreglass. Each varies in cost, lifespan, and suitability for different applications.

Which is best, EPDM or GRP?

For most domestic flat roofs, EPDM is the better choice due to its flexibility and longer lifespan. GRP is better for roof terraces and walkable surfaces where a rigid, impact-resistant finish is needed.

What is a 3 layer flat roof system?

This usually refers to built-up felt roofing, where multiple layers of bitumen felt are applied and bonded together to create a waterproof system. It is a traditional approach that has largely been replaced by single-membrane systems like EPDM.

What type of roof is best for a flat roof?

EPDM is generally considered the best all-round system for domestic flat roofs in the UK. It combines long lifespan, low maintenance, and good value over time.

Which is better, EPDM or PVC flat roof?

For most UK domestic applications, EPDM is the more practical choice. It is widely used, well-proven, and handles the UK’s temperature variation better than PVC, which can become brittle in cold weather.

How long does a GRP flat roof last?

A GRP fibreglass flat roof typically lasts 25 to 40 years when correctly installed. It requires little maintenance but should be inspected periodically for cracking or impact damage.

Is EPDM the same as rubber roofing?

Yes. EPDM is the technical name for the synthetic rubber membrane commonly called rubber roofing. EPDM stands for Ethylene Propylene Diene Monomer.

Can you walk on a flat roof?

A GRP fibreglass roof can be walked on regularly. EPDM can handle occasional traffic but should not be used as a regular walking surface without protection boards. Felt roofs should not be walked on.

Do flat roofs need a fall?

Yes. All flat roofs should have a minimum fall of 1:80 (about 1.25 percent) to allow water to drain. A flat roof that pools water is a maintenance and structural concern.

How much does a GRP flat roof cost?

For a 20 to 25 square metre extension or garage, expect to pay roughly £1,800 to £3,500 for a GRP installation, depending on complexity and access.

Can felt be replaced with EPDM?

Yes. Replacing an old felt roof with EPDM is a common and worthwhile upgrade. The existing deck may need inspection and possible replacement, but the switch is straightforward for an experienced flat roofing contractor.

What causes flat roofs to fail?

Poor drainage, installation defects, prolonged UV exposure on felt systems, and building movement causing membrane cracking are the most common causes of flat roof failure.

How is an EPDM roof fitted?

The rubber membrane is bonded to a prepared roof deck using adhesive and then trimmed and dressed into edges, outlets, and upstands. For larger roofs, seams may be needed, which are bonded using special tape and adhesive.

Are flat roofs covered by insurance?

Most standard home insurance policies cover flat roofs, though some insurers apply conditions or age restrictions for older felt systems. Check your policy wording and be transparent about the age and type of flat roof when taking out cover.