GRP Flat Roof

A Complete Guide

The GRP or fibreglass flat roof is one of the most widely used systems in the UK and is found not only on large commercial buildings but smaller domestic properties as well. It is highly popular because it is easy to lay, requires no heat, comes at a competitive cost and lasts for a long time.

Whether you want to replace an existing flat roof or build an entirely new one, understanding how a GRP flat roof works is important.

Here we take a closer look at this roofing system, why it is better than other approaches such as felt and asphalt and we will explore how to find the right GRP flat roof installer for your property.

What is a GRP Flat Roof?

GRP stands for Glass Reinforced Polyester, more commonly known as fibreglass. The process of using this for flat roofing has been around for more than 60 years. It is a system that has developed quite a lot over the last 20 years and today’s cold-applied systems are durable and cost-effective.

Our Topseal GRP flat roof system is one of the best in the UK and is used on both domestic properties and large businesses across England, Wales, Scotland, and Northern Ireland.

Fibreglass roofing can be laid in a relatively short time and cover large areas such as warehouses and industrial complexes. The chances are that many of the flat roofs that you see on commercial premises from your office are created using fibreglass.

What Are The Benefits of a GRP Flat Roof?

There are several benefits of fibreglass flat roofing systems over other types of installation:

  • GRP flat roofs are safer to install: Other types of roofing require the application of high levels of heat which can be damaging and sometimes dangerous if not properly applied. GRP flat roofs are applied cold using a special resin that cures when a catalyst is added.
  • Fibreglass is suitable for any shape roof: The flexibility of GRP flat roofing means that it can easily be applied to both large areas and small as well as fit any design. Materials can be cut to the shape of the roof and the appropriate trims used to cover a surface effectively.
  • GRP flat roofs are strong and durable: If you spend money on putting down a new roof, you want it to last. Fibreglass is one of the most durable materials in construction today which is why these systems tend to come with lengthy warranties of more than 20 years. Well maintained, you can realistically expect a Topseal applied flat roof to last a lifetime.

Because there are no seams in the roof and an effective waterproof covering is used, there is little opportunity for cracks to develop causing leaks, even after many years. If repairs are needed at any point, the whole roof can remain intact and specific areas treated. That makes it cost-effective even in the long term.

Can You Walk on a Fibreglass Roof?

Yes, you can walk on a fibreglass roof. There are different grades of GRP flat roofing that are suitable for different circumstances. If you want to create a walkway or patio area for a bar or restaurant, GRP flat roofing systems are ideal.

Our Topseal HD GRP roof system, for example, provides extra durability and is completely waterproof and comes in a range of finishes. It’s also accompanied by a 30-year guarantee.

Can I Install a GRP Flat Roof on My Home?

Many homes have a balcony or flat roof area that can be replaced with a fibreglass system. You may just want to replace an old roof, or you might want to transform it into an area where you can sit and catch some sun on Summer days.

Another option is to transform a small area of flat roof into a garden which will improve biodiversity and benefit the local ecology.

How is a GRP Flat Roof Installed?

Compared to some other roofing systems, a GRP flat roof is relatively easy to install. It uses a cold application of resin that is layered between fibreglass matting to create a waterproof and durable covering.

The key to a successful GRP flat roof is in the preparation. The joists need to be in good condition with the OSB3 deck completely dry and clean. For small roofing areas, the preparation can often take longer than the laying of the fibreglass covering itself. Perimeter trims are added to the roof to provide a nice neat finish around the edges of the roof.

A catalysed resin layer is put down over the decking, using a roller to cover the deck. Fibreglass reinforcement matting which has been pre-cut and fitted to the area that needs to be covered is then rolled out over the surface.

A second layer of resin is put over this. The resin and matting is then consolidated by using a paddle roller which eliminates are bubbles and makes the laminate completely water tight. The resin is then left which takes between 60 – 90 minutes. Once the resin layer is cured, a topcoat is applied which protects the laminate from UV damage and provides fire protection.

Because the method is so quick, large areas such as warehouses and industrial buildings can be covered in a relatively short time. The fact that this is all cold applied means there are no health and safety issues.

How Much Does a Fibreglass Flat Roof Cost?

Several factors affect the final cost of a GRP flat roof. The first is whether you are building a new roof or replacing or repairing an old one. With a new roof, you will need to build the frame or decking on which the fibreglass will be placed.

The other factor is the size, complexity of the roof and location. Please contact Topseal to find your local Approved Topseal.

Should I Have a Fibreglass Roof Repair?

In the unlikelihood of a GRP roof needing a repair, the good news is that repairing them is relatively easy. Individual sections can be repaired without having to take up the whole roofing and replace it. If you have an existing fibreglass roof, then this is well worth considering if you are on a tight budget.

Is a GRP Flat Roof Better Than Other
Roofing Solutions?

There are other flat roofing systems such as reinforced bitumen, asphalt and EPDM. All of these have their good and bad points. Bitumen, for example, requires heat to apply and can be difficult to repair in patches but it is durable.

GRP flat roofs are easy to put down, durable and long-lasting which means that they have a big advantage over other systems. Because they can be laid in a relatively short time and have competitive costing attached to them, they are also the most popular kind of flat roofing seen in the UK.

How Long Does a GRP Flat Roof Last?

In the unlikelihood of a GRP roof needing a repair, the good news is that repairing them is relatively easy. Individual sections can be repaired without having to take up the whole roofing and replace it. If you have an existing fibreglass roof, then this is well worth considering if you are on a tight budget.

Should I Get a GRP Flat Roof Kit?

You can buy DIY GRP flat roof kits that are obviously cheaper than a professional installation, however this can often prove to be false economy. Being in the UK the weather usually isn’t on our side, particularly with the extreme Winter’s we have endured over recent years, everything from snow to gale force winds has hit us, and your roof needs to be durable enough to deal with these elements.

DIY roof kits do not usually come with any form of warranty. When it comes to your roof and keeping your property secure from the elements, a Topseal installation is the solution of choice for those wanting peace of mind.

What Types of GRP Flat Roof Are There?

There are several different GRP flat roof products available on the market today and a lot will depend on what you are going to use the surface for. At Topseal we provide a range of different systems for our installers.

  • The standard Topseal is ideal for areas of flat roofing in domestic properties and some commercial premises.
  • Topseal HD is a much more hard-wearing system and is designed for areas where you are likely to have a good deal of footfall.
  • Topseal PU is a polyurethane high-performance flat roofing system used on large commercial properties.
  • Topseal Greentop, on the other hand, is a flat roof system that has been specially designed for creating garden spaces or green roofs.

It is important to talk through what you want from your GRP flat roof system with your installer so that you get the durability you are looking for as well as value for money.

How Do I Find a Professional GRP Flat Roof Installer?

There are thousands of flat roofing specialists across the UK. At Topseal, we only allow our unique products to be installed by companies and individuals who have been through our extensive training course and met the high standards that we set. This is one way that we ensure each roof using our system is fit for purpose and built to last as well as looking aesthetically appealing.

How Do I Verify a Topseal GRP Flat Roof Installer?

If you are searching for a Topseal GRP flat roof installer or want to make sure they are registered with us, you can quickly visit our website and check their number against our verification database.



Every Topseal installer is allocated a unique verification number to prevent 3rd party misrepresentation. You should always ask any Topseal installer for their verification number.

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