If you’re researching flat roof options, you’ve probably come across the term GRP roofing. It’s one of the most popular systems in the UK for garages, extensions, and even balconies.
A fibreglass roof, also known as GRP, is renowned for its aesthetic appeal, durability, and longevity. Available in different colours, it offers a seamless, waterproof finish that is both impact-resistant and easy to maintain. A properly installed fibreglass roof can outperform traditional roofing options in both lifespan and efficiency.
But what is GRP roofing—and is it a good choice for your home or business?
At Roofing Newcastle, we’ve installed GRP systems across hundreds of properties throughout the North East. In this guide, we’ll break it all down clearly so you know what you’re getting.
Introduction to GRP Roofing
GRP (Glass Reinforced Plastic) roofing is a popular choice for flat roofs due to its durability, waterproofing properties, and ease of installation. GRP roofing systems are made from a composite material consisting of polyester resin and glass fibre strands, which provide exceptional strength and resistance to weathering and corrosion. This combination results in a robust and resilient roofing solution that can withstand the elements and maintain its integrity over time.
One of the standout features of GRP roofing is its impressive lifespan. With proper installation and minimal maintenance, a GRP roof can last up to 30 years, making it an excellent investment for homeowners and businesses alike. The seamless, watertight finish of GRP roofing ensures that water cannot penetrate the surface, preventing leaks and water damage. This makes GRP roofing an ideal choice for those looking for a reliable and long-lasting roofing solution for their flat roofs.
What Does GRP (Glass Reinforced Plastic) Stand For?
GRP stands for Glass Reinforced Plastic—also known as fibreglass roofing. GRP stands for glass-reinforced plastic, a composite material known for its strength and durability.
It’s a cold-applied flat roofing system made by layering resin and fibreglass matting over a roof deck, then finishing it with a topcoat to form a seamless, waterproof surface.
The result is a hard, durable, and fully bonded roof with no joints, seams, or weak spots where water could get in.
How Does Fibreglass Roofing Work?
Here’s how a GRP flat roof is typically installed:
- A plywood or OSB roof deck is laid down on the roof structure. It is crucial to securely attach the roofing boards to the roof joists before applying the laminating materials.
- A layer of fibreglass matting is placed over the deck
- Liquid resin is applied and brushed into bond the layers
- Once dry, a coloured topcoat is added for UV protection and a smooth finish
The installation process creates a single, continuous waterproof membrane that’s incredibly tough and long-lasting.
At Roofing Newcastle, we install GRP using BBA-approved systems to ensure every roof meets the highest standards.
GRP Roofing Materials and Construction
GRP roofing materials are designed to provide a seamless, watertight finish that is built to last. The construction of a GRP roof typically involves the following components:
- Polyester resin: This liquid material cures into a solid with the help of a catalyst, forming the base of the GRP roofing system. The polyester resin is essential for creating a strong and durable bond between the layers of the roof.
- Glass fibre strands: These are used in the form of chopped strand mat (CSM) or woven roving, which provide reinforcement and strength to the roofing material. The glass fibre strands are embedded in the resin, creating a composite material that is both lightweight and incredibly strong.
- Topcoat: A premixed resin topcoat is applied to seal the roof and provide additional protection. The topcoat not only enhances the roof’s appearance but also offers UV resistance and weatherproofing, ensuring the roof remains in excellent condition for years to come.
- Trims: Preformed trims are installed around the edges of the roof to provide a secure fit and prevent water ingress. These trims are essential for maintaining the integrity of the roof and ensuring a neat, professional finish.
GRP roofing systems can be installed on various substrates, including OSB (oriented strand board) with tongue and groove edge, and can be used on flat roofs, pitched roofs, and even curved roofs. This versatility makes GRP roofing an attractive option for a wide range of applications, from residential extensions to commercial buildings. The seamless, watertight finish and exceptional durability of GRP roofing materials make them a reliable and long-lasting choice for any roofing project.
Where Is GRP Roofing Used on Flat Roofs?
GRP roofing is commonly used on:
- Garages
- Extensions
- Dormer roofs
- Porches
- Bay windows
- Balconies and terraces (with anti-slip finish)
- Commercial flat roofs
Because of its durability and modern appearance, GRP is often chosen for visible flat roof areas where aesthetics matter too. GRP flat roofing is suitable for various types of projects, from residential to commercial.
Benefits of GRP Roofing
1. Fully Waterproof
Once cured, GRP forms a seamless membrane that water simply can’t get through. No joints = no leaks. Glass fibres are an integral component in the manufacturing of GRP laminates, enhancing the material’s durability and ensuring watertight performance.
2. Long Lifespan
A well-installed GRP roof can last 20–30 years or more with minimal maintenance.
3. Low Maintenance
No loose tiles, no joints, and no seams mean fewer problems over time.
4. Attractive Finish
GRP roofs are neat, modern, and available in various colours. Ideal for visible roofs on extensions or porches.
5. UV and Weather Resistant
The topcoat protects against sunlight, rain, frost, and temperature changes—keeping the roof looking fresh.
6. Safe to Install
Because it’s a cold-applied system, there’s no need for heat or torches during installation. That makes it safer for your home and surrounding property.
7. Can Be Walked On
With the right finish, GRP can be used for balconies or terraces. Anti-slip topcoats are available for extra safety.
Are There Any Downsides?
While GRP has plenty of advantages, it’s not perfect for every roof. A few things to consider:
- Only suitable for flat or low-pitch roofs (below 10 degrees)
- Must be installed in dry conditions—rain can ruin the curing process
- Not ideal for very large roofs unless expansion joints are added
- Needs professional installation—DIY attempts often fail due to incorrect resin ratios or poor layering
At Roofing Newcastle, we make sure every GRP roof is applied with care, precision, and in the right weather conditions.
How Much Does GRP Roofing Cost?
In the UK, GRP roofing typically costs between £70 and £90 per square metre, fully installed.
So for a standard single garage (around 15m²), you’re looking at:
- £1,050 to £1,350 in total
Costs can vary depending on:
- Roof size and access
- Condition of the existing deck
- Optional extras (e.g. trims, anti-slip coating)
- Waste removal or edge detail requirements
We provide free site visits and quotes across Newcastle and surrounding areas.
How Long Does GRP Roofing Take to Install?
Most small to mid-sized GRP roofs can be completed in 1 to 2 days—weather permitting.
Larger or more complex roofs may take longer, especially if the deck needs repairs or replacement. We always aim to minimise disruption and get the job done right the first time.
Is GRP Roofing Better Than Felt?
GRP is more durable, longer-lasting, and has a neater finish than traditional felt. It also doesn’t rely on heat during installation.
However, felt is cheaper upfront and may still be suitable for low-budget projects or outbuildings.
We often recommend GRP to homeowners looking for a longer-term investment, especially for visible flat roofs where aesthetics matter.
Final Thoughts
So—what is GRP roofing?
It’s a high-performance, fibreglass-based flat roofing system that’s fully waterproof, long-lasting, and low maintenance. Ideal for garages, extensions, and balconies, it offers great value for money and a clean, modern look.
At Roofing Newcastle, we’ve been installing GRP roofs across the North East for years. If you’re considering a flat roof replacement or new installation, we’ll help you decide whether GRP is the right fit for your home or business.
Contact us today for a free quote, friendly advice, and professional installation you can count on.
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