A fibreglass roofing system (also known as glass fibre or a GRP roofing system) is a composite made out of resin with glass fibre strands, which makes it strong, lightweight, waterproof and durable. It doesn’t have seams, so leaks are less common, and repairs are simple. GRP roofing offers excellent value and is an easy-to-lay flat roof option, as it doesn’t need additional heat to set, making it safer to install too.

What is GRP roofing?

GRP stands for ‘glass reinforced plastic’, and is sometimes called ‘glass reinforced polymer’, ‘glass reinforced polyester’ or FRP (‘fibre reinforced plastic’). GRP roofing meaning is the same as a fibreglass roof, as it combines thermosetting polyester resin with glass fibres. A GRP flat roof is the ideal choice for domestic and commercial projects as it is reliable and long lasting, whilst offering excellent insulation. Although it can be more expensive than felt roofing, it lasts longer and is more resistant to damage over time.

Advantages of GRP and fibreglass roofing

A fibreglass roof (or GRP flat roof) is an ideal way to achieve a versatile and secure flat roof which avoids leaks and cracking. The main advantages of a GRP roof system are:

Strong and durable: fibreglass is known to offer strength and durability, as it is impact resistant, and it can even be walked on after being installed. It’s fast drying too
Long lasting: with no joins, GRP flat roofs are a high-performance solution which can last over twice as long as felt roofs, often in excess of 30 years
Waterproof: fibreglass roofing systems are seamless and resin bonded, making them completely waterproof, reducing the risk of water damage over time
Versatile: lightweight and flexible, GRP roofing systems can be moulded to a variety of shapes and sizes, including pitched roofs. It can be finished to a specific colour, and offers less wastage than felt roofs
Safe: as well as offering structural safety due to being both lightweight and strong, fibreglass roof materials are safer to install as they don’t require high heat but a cold resin and catalyst to cure them
Convenient and easy to maintain: the seamless structure reduces the likelihood of cracking and damage. When damage does occur, it’s often a simple repair job rather than needing to replace the whole roof
Value for money: although fibreglass roofs are more expensive than felt roofs, they last a lot longer, representing excellent value for money over the roof’s lifetime. In the UK on average, a fibreglass roof can cost anywhere from £75 to £200 per m2. The price can vary depending on some factors like roof specifications, build-up, and finishes.

Applications and suitability

As well as looking good and lasting a long time, fibreglass and GRP roofing can be made to fit pretty much any size area. Because of its versatility and durability, it’s frequently used for smaller domestic properties as well as large industrial and commercial buildings.

Waterproof fibreglass roofing systems are perfect for flat roof areas, from buildings to out houses, and because they last so long and have a sleek appearance they are a good choice for extensions and refurbishments. As they can usually be finished to a specific colour, they can be used for character properties through to ultra modern architecture.

GRP roofing systems are also ideal for creating balcony areas, walkways, or even feature garden and outdoor areas on flat roof areas. The strong and waterproof properties make it a good alternative to asphalt flat roofs or tiles when creating raised areas with low or even high footfall.

Installation and maintenance considerations

It’s important to have a fibreglass roof installed by a professional contractor, to ensure it is laid correctly and lasts as long as possible.

The installation process is fairly simple, which is why it’s a popular roofing option for all sorts of projects.

Before installing, the roof deck must be prepared and any previous roofing materials removed. It’s vital at this stage that the decking underneath is dry. A professional contractor will likely make sure a drainage system is in place, to prevent water from pooling on the new roof
The boards are then laid and securely attached to the roof joists
The fixing trims are installed all around the roof
The resin is then mixed ready for laminating the roof, and the catalyst is added to cure it
The chopped strand mat is laid, followed by the main fibreglass laminate
Finally, the premixed resin top coat is applied to seal the roof

Before installing, it’s important to consider:

Fibreglass roofing systems mustn’t be installed when it’s raining, as too much moisture can interfere with the resin when it’s hardening
Ideally, it shouldn't be too hot or too cold. If the temperature is above 30 degrees C, it can melt the roofing materials and prevent the catalyst from working. It’s also best to work out of the direct sun if possible for the same reason. At freezing or below, the resin also won’t cure
The laminate should be applied in short runs, and only a small amount of resin mixed at once, to prevent the roof from hardening too quickly
Cured resin stays in place. Make sure it’s not too windy, remove nearby vehicles and equipment, and mask off any areas - such as skylight windows - in case of splashing

One of the main benefits of GRP roof systems is their low-maintenance upkeep. It’s important to note:

Although more expensive than asphalt, the long life of a GRP roof makes it a cost-effective alternative
If leaks or cracks occur, they are usually simple to fix without replacing the whole roof
After installation, homeowners are recommended to have their roof guttering cleared regularly, to avoid debris building up and allowing excess water to build up

Fibreglass & GRP roofing: FAQs

Is fibreglass and GRP the same?

GRP roofing is another term for fibreglass roofing, or fibre reinforced plastic roofing. It’s a flat roof composite which is made from resin with glass or fibre strands to make it strong, waterproof, versatile, long lasting and easy to lay.

How long does a GRP roof last?

A professionally-laid fibreglass roof can last between 25 and 30 years, but if it’s well looked after it can last much longer. Its strength, impact resistance and easy-to-repair structure make it a popular choice for homeowners. Maintenance of your flat roof could help it last up to 50 years, by avoiding fading and cracks appearing from extreme weathering.

How often do you need to replace a fibreglass roof?

Fibreglass roofing systems are usually chosen for their ability to last upwards of 25 years without needing to be replaced. Most manufacturers guarantee at least 20 years before needing a replacement, but many last a lot longer. GRP flat roof details are easy to repair, and sometimes a new fibreglass layer can be added to avoid needing to replace the whole roof.

Can you walk on GRP roofing?

Yes, you can walk on a professionally installed GRP roof system. How frequently the roof will be walked on will dictate the GRP grade for the project. If you’re creating a walkway or balcony designed to be regularly walked on, you may need up to two layers of matting for your roof.

How long does fibreglass roof take to dry?

Depending on the outside temperature, a GRP roof should be cured to the touch in around an hour. However, it can take up to three days for the roof to be fully hardened. It is recommended to only install a fibreglass roof in dry weather, and when the temperature is above 5°C and below 30°C, as very hot or cold temperatures mean it will not cure.

GRP roof systems (otherwise known as fibreglass roofing systems) offer a durable, easy to lay and reliable alternative to felt roofing for projects requiring a flat roof. Not all repairs to flat roofs need Building Regulations approval, but it’s best to check with your local Building Control office before starting work. Don’t forget, our Travis Perkins Trade News and Advice centre has information on the latest Building Regulations, as well as handy guides for any construction project.

Disclaimer: The information contained on this page is intended as an overall introduction and is not intended as specific advice from a qualified professional. Travis Perkins aims to avoid, but accepts no liability, in the case that any information stated is out of date.

Always refer to the manufacturer's guidance for installation instructions and product maintenance.

Fibreglass and GRP Roofing

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What is fibreglass roofing?