Flat Roof Options in the UK: EPDM, GRP and Felt Explained

Flat roofs are commonly used on garages, extensions, porches, commercial buildings and outbuildings across the UK. They are practical, cost effective and suitable for areas where a pitched roof may not be possible.

However, choosing the right system matters. The best flat roof material depends on your budget, the size of the roof, how the space is used and how long you want the roof to last.

This guide from Northern Heritage Roofing explains the main flat roof options in the UK, including EPDM, GRP fibreglass and torch on felt, along with typical costs, lifespan, drainage and maintenance.

What Is a Flat Roof?

A flat roof is a roofing system with a very shallow slope rather than a traditional pitched design.

Although it looks flat, the surface should still have a slight fall so rainwater can move towards gutters, outlets or drainage points.

Flat roofing is often used on extensions, garages, commercial properties, dormers and smaller buildings.

What Are the Main Types of Flat Roofing?

The three most common flat roofing systems used in the UK are:

EPDM rubber roofing

GRP fibreglass roofing

Torch on felt roofing

Each system has different costs, installation requirements and expected lifespan.

1. EPDM Rubber Roofing

EPDM stands for ethylene propylene diene monomer. It is a durable rubber membrane widely used for domestic and commercial flat roofs.

How Does EPDM Roofing Work?

EPDM is usually installed in large sheets over a prepared roof deck.

Because large areas can often be covered with very few joins, there are fewer potential weak points where water can enter.

The rubber membrane is flexible and can cope with temperature changes without becoming brittle.

How Long Does an EPDM Roof Last?

A properly installed EPDM roof can typically last around 25 to 30 years, and sometimes longer with good maintenance.

Keeping gutters and drainage outlets clear can help prevent unnecessary standing water and extend the life of the membrane.

How Much Does EPDM Roofing Cost?

Typical installed prices may fall between around £70 and £100 per square metre.

Costs vary depending on roof size, access, insulation, preparation work and the condition of the existing roof deck.

2. GRP Fibreglass Roofing

GRP means glass reinforced plastic. It is a rigid roofing system that creates a smooth and seamless waterproof surface.

How Does GRP Roofing Work?

GRP roofing is normally applied over a timber roof deck.

Resin and fibreglass matting are combined to create a solid waterproof layer before a protective topcoat is added.

Because the finished surface has very few joints, GRP can provide reliable protection against water penetration when installed correctly.

How Long Does a GRP Roof Last?

A good quality GRP fibreglass roof can commonly last around 20 to 25 years.

Its hard surface is also useful on roofs that may occasionally need to support light foot traffic for maintenance.

How Much Does GRP Roofing Cost?

GRP installation may typically cost between £80 and £120 per square metre.

The final price depends on the roof shape, access, preparation requirements and whether insulation or deck replacement is required.

3. Torch On Felt Roofing

Torch on felt remains a popular option for garages, sheds, extensions and utility buildings.

How Does Felt Roofing Work?

Modern felt roofing uses layers of modified bitumen.

The sheets are bonded together using heat to create a waterproof roof covering.

Multiple layers provide additional protection, although good installation is particularly important around edges, joints and outlets.

How Long Does a Felt Roof Last?

A professionally installed felt roof may last around 15 to 20 years.

Regular inspection and prompt repairs can help extend its usable life.

How Much Does Felt Roofing Cost?

Torch on felt is generally one of the more affordable flat roofing options.

Installed costs may fall around £45 to £70 per square metre depending on the size and complexity of the job.

Which Flat Roof Material Is Best?

There is no single flat roof system that is best for every property.

EPDM is a good choice where flexibility, long lifespan and low maintenance are priorities.

GRP works well where homeowners want a clean, hard and seamless finish.

Felt is often suitable where budget is important or where the roof covers a garage, shed or utility area.

A roofing contractor should assess the roof before recommending a system.

What Is the Best Flat Roof for an Extension?

For a domestic extension, EPDM and GRP are both popular choices.

GRP offers a neat, solid finish, while EPDM provides a flexible membrane with very few joints.

The right choice depends on the shape of the roof, access, drainage and overall budget.

What Is the Best Flat Roof for a Garage?

All three systems can be suitable for garage roofs.

Felt may be attractive if keeping costs lower is important.

EPDM can provide a longer service life with relatively little maintenance.

GRP can also work well where a strong and tidy finish is preferred.

How Much Does a Flat Roof Cost in the UK?

Flat roof prices can vary considerably.

As a general guide, felt may cost around £45 to £70 per square metre, EPDM around £70 to £100 and GRP around £80 to £120.

These figures can change depending on access, insulation, roof deck condition, scaffolding and the size of the project.

A proper roof survey is the best way to get an accurate quotation.

How Long Should a Flat Roof Last?

A flat roof may last anywhere from around 15 years to more than 30 years depending on the material and quality of installation.

Regular maintenance also makes a difference.

Poor drainage, damaged membranes and neglected leaks can shorten the life of any roofing system.

Why Is Drainage Important on a Flat Roof?

Water should not remain on a flat roof for long periods.

Poor drainage can lead to pooling water, additional weight, membrane deterioration and leaks.

Gutters and outlets should be kept clear of leaves, moss and debris.

What Fall Does a Flat Roof Need?

A flat roof should have a slight slope to help rainwater drain naturally.

A common design target is around 1:80 for the finished roof, although requirements depend on the roofing system and construction method.

The correct fall should be planned during installation rather than relying on the membrane alone.

Does a Flat Roof Need Insulation?

Insulation is important for flat roofs covering heated living spaces.

Good insulation helps reduce heat loss and can also help control condensation.

The correct build up depends on whether the roof uses a warm roof or another construction method.

What Is a Warm Flat Roof?

A warm flat roof places insulation above the structural roof deck.

This helps keep the deck warmer and reduces the risk of condensation forming within the roof structure.

Warm roof construction is commonly used on modern extensions and habitable rooms.

Does Flat Roofing Need Planning Permission?

Replacing an existing flat roof may not always require planning permission, but extensions, major alterations and work on certain properties can be subject to additional rules.

Building Regulations may also apply, particularly where insulation or structural work is involved.

If you are unsure, check the requirements before work begins.

Should You Repair or Replace a Flat Roof?

A small localised leak does not always mean the entire roof needs replacing.

Minor splits, damaged sections or small areas of blistering may be repairable if the rest of the roof is sound.

Replacement may make more sense when the roofing system is old, repeatedly leaking or showing widespread deterioration.

What Are the Signs a Flat Roof Needs Replacing?

Common warning signs include leaks, cracks, blistering, pooling water, a damaged membrane, poor drainage, damp patches and a rotten roof deck.

Repeated repairs are another sign that the roof may be reaching the end of its useful life.

How Can You Maintain a Flat Roof?

Inspect the roof regularly and keep drainage clear.

Remove leaves and debris, look for damaged areas and check around edges and outlets.

Small problems are usually easier and cheaper to deal with before they develop into larger leaks.

How to Choose a Flat Roofing Contractor

Look for a contractor with experience installing the roofing system you are considering.

Ask for a clear written quotation that explains materials, preparation work, insulation, waste removal and guarantees.

Northern Heritage Roofing can assess the condition of your roof and explain whether repair or replacement is the more practical option.

Frequently Asked Questions

Is EPDM better than GRP?

Not always. EPDM is flexible and long lasting, while GRP provides a strong, seamless finish. The right choice depends on the property and roof design.

What is the longest lasting flat roof material?

EPDM is often among the longer lasting common flat roof systems and may provide 25 to 30 years of service when properly installed and maintained.

How much does a new flat roof cost?

Prices vary by material, size, access and roof condition. Typical costs may start around £45 per square metre for felt and rise above £100 per square metre for some GRP projects.

Can you repair a leaking flat roof?

Yes. Small leaks can often be repaired if the surrounding roofing material and roof deck remain in good condition.

How often should a flat roof be inspected?

It is sensible to check a flat roof at least once or twice a year and after severe weather.

Can water sit on a flat roof?

Small amounts may remain briefly after heavy rain, but persistent pooling can indicate poor drainage or an incorrect roof fall.

Does a flat roof need insulation?

A flat roof covering a heated room will normally require appropriate insulation to improve energy efficiency and reduce condensation risk.

How long does flat roof installation take?

A small straightforward flat roof may be completed relatively quickly, while larger or more complex projects can take several days. Weather, access and roof deck repairs can all affect the timescale.

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