If you’ve been researching modern flat roof solutions, you’ve probably noticed one material being mentioned again and again: GRP roofing.
Over the past decade, we’ve seen a significant rise in customers choosing GRP roofing for extensions, garages and commercial buildings. But what’s behind this growth? Is it just a trend, or does it genuinely outperform other systems?
At AL King Roofing Ltd, we believe in giving you honest, practical advice. In this guide, we’ll explain:
- What GRP roofing actually is
- The pros and cons you should consider
- How it compares to other flat roof solutions
- Where it can be installed
- How to maintain it properly
- And whether it’s right for your property
If you’d like tailored advice at any point, please contact us; we’re always happy to help.
What Is GRP Roofing?
GRP stands for Glass Reinforced Plastic. You may also hear it referred to as glass reinforced roofing or fibreglass roofing.
It’s a system that combines polyester resin with glass fibres to create a strong, fully bonded, seamless surface. GRP is a composite material, often called glass reinforced polyester, made by embedding glass fibre strands within the resin. Once cured, it forms a hard, durable shell over your roof deck. The GRP laminate is created by building up multiple layers of fibreglass mat and resin, which are then cured to form a seamless, waterproof surface.
Unlike traditional felt systems, GRP roofing creates a single-piece, waterproof GRP membrane with no joins across the main surface, which significantly reduces the risk of leaks.
That seamless finish is one of the key reasons GRP roofing continues to grow in popularity.
If you’re considering a flat roof installation, get in touch, and we’ll explain whether GRP is the right option for you.
Why Is GRP Roofing Becoming So Popular?
There are several reasons homeowners and commercial property owners are moving towards GRP roofing.
Seamless Waterproof Protection
One of the biggest causes of flat roof failure is seam breakdown. Traditional felt systems rely on overlaps, which can weaken over time.
GRP roofing eliminates this problem by forming a continuous waterproof GRP membrane across the surface. This creates a joint free surface, further reducing the risk of water ingress.
Fewer seams = fewer potential leaks.
Long Lifespan
When installed professionally, GRP roofing can last 25–40 years or more. GRP systems are long-lasting and offer a long life due to their resistance to corrosion and UV-resistant top coats, which protect against sun damage. Compared to older felt systems (which may last 10–20 years), that’s a significant improvement.
Longevity is one of the key reasons customers choose GRP as part of their long-term flat roof solutions. GRP roofing also requires minimal upkeep compared to traditional felt systems, further contributing to its long life.
Strength & Durability
Glass reinforced roofing is extremely tough once cured. It resists:
- Impact damage
- It is extremely strong and can be specified with two layers of fibreglass matting for areas subject to heavy foot traffic, such as walkways and balconies.
- UV exposure
- Weathering
- Foot traffic (when finished appropriately)
It creates a rigid surface that holds up well in British weather conditions.
Modern Appearance
GRP provides a smooth, clean finish that suits contemporary properties. It can also be finished in various colours to complement your home.
For many customers, aesthetics matter just as much as performance.
If you’re planning a modern extension, reach out to your team, and we’ll show you examples of recent GRP projects.
Where Can GRP Roofing Be Installed?
One of the reasons GRP roofing keeps growing in popularity is its versatility. It’s not just for flat garages; it can be used in a wide range of applications. Proper installation of GRP roofing requires a well-prepared decking, typically OSB3, to ensure durability and strong adhesion of the fibreglass laminate.
Here’s where GRP performs particularly well:
Flat & Low-Slope Roofs
This is its primary use. GRP roofing is also highly suitable for low-pitched roofs, such as those found on garages, extensions, and outbuildings.
Flat roofs are vulnerable to standing water, but the seamless nature of a waterproof GRP membrane prevents the pooling issues often seen with older systems.
Because the membrane is fully bonded, water cannot track beneath it easily, making it ideal for:
- Extensions
- Garages
- Garden rooms
- Commercial flat roofs
If you’re upgrading a flat roof, contact us to discuss whether GRP is the best fit.
Pitched Roofs
GRP isn’t limited to flat surfaces.
It can also be used on pitched roofs as a modern, lightweight alternative to tiles or slate. This is particularly popular for:
- Contemporary architectural designs
- Minimalist builds
- Outbuildings
It provides a sleek, clean finish that differs from traditional tiled roofs.
Complex Detailing
This is where GRP truly excels.
Because it’s applied as a liquid resin before curing, it can adapt to:
- Dormer windows
- Parapet walls
- Curved or barrel-vaulted roofs
- Unusual architectural features
Because the material can be moulded to fit complex shapes, it ensures a precise, watertight seal even on intricate roof designs.
GRP can be easily moulded around complex shapes and architectural details, providing a watertight and seamless finish.
Tiles and some membranes struggle with complex detailing, but glass reinforced roofing can mould seamlessly around these areas.
Walkways & Balconies
Thanks to its high strength-to-weight ratio, GRP roofing is suitable for areas with foot traffic.
With a non-slip finish applied, it’s often used for:
- Roof terraces (GRP roofing can be laid with thicker fibreglass mats to create a durable, waterproof surface suitable for a terrace that is regularly walked on)
- Balconies
- Walkways
- Access areas
If you need a durable walking surface, give us a call today, and we’ll advise on suitable finishes.
The Pros of GRP Roofing
Let’s break down the advantages clearly.
GRP systems are recognised for their durability, seamless waterproofing, and versatility across a range of flat roofing applications.
Fully Seamless System
Reduces leak risk.
Lightweight Yet Strong
Less structural stress compared to some materials.
Long Lifespan
Outperforms traditional felt systems.
Low Maintenance
Requires minimal ongoing upkeep.
UV & Weather Resistant
Performs well in UK conditions.
Suitable for Complex Roof Shapes
Excellent for detailed work.
When installed properly, GRP roofing provides a highly reliable flat roof solution.
The Cons of GRP Roofing
No roofing system is perfect. Transparency matters, so here are some considerations: While the initial cost of GRP roofing may be higher than some alternatives, its long-term durability and low maintenance can make it more cost-effective over time.
GRP must be installed in dry conditions. Installation should be avoided during periods of frost, high heat, or cold, as these conditions can negatively affect the curing process and the final quality of the roof. Moisture or unsuitable temperatures can lead to improper curing, which may compromise the roof’s weather resistance and longevity.
Repairs to GRP roofing are generally straightforward, as the material allows for easy patching and maintenance without extensive removal or structural work. However, repairs must be carried out in dry weather and mild temperatures to ensure proper adhesion and curing.
Installation Conditions
GRP must be installed in dry conditions. Rain or excessive moisture during installation can affect curing.
Skilled Installation Required
Poor workmanship can result in cracking or bubbling. Professional expertise is essential.
Surface Rigidity
Because GRP forms a rigid shell, it may not be as flexible as rubber systems if structural movement occurs.
This is why professional assessment is vital before choosing your flat roof solution.
If you’re unsure whether GRP suits your building, get in touch, and we’ll assess your structure properly.
GRP Roofing vs Other Flat Roof Solutions
When comparing GRP to other flat roof solutions like EPDM or PVC, GRP roofing provides a robust cover that shields the underlying structure from water ingress and weather damage.
GRP vs EPDM (Rubber Roofing)
- GRP is rigid and seamless.
- EPDM is flexible and elastic.
- GRP often offers a harder finish suitable for foot traffic.
- EPDM may perform better on buildings prone to movement.
GRP vs Felt
- GRP lasts longer.
- GRP has fewer seams.
- GRP requires less maintenance over time.
Each system has strengths, and we’ll always recommend what’s right for your property, not just what’s popular.
Maintenance: How to Look After GRP Roofing
One of the biggest advantages of GRP roofing is its low maintenance requirement.
However, like any roofing system, it benefits from periodic care.
Annual Visual Inspection
Check for cracks, surface damage or debris build-up.
Keep It Clean
Remove leaves, moss and dirt to prevent blocked outlets.
Check Drainage
Ensure water drains freely. Even the best waterproof GRP membrane performs better with proper drainage.
Professional Inspections
We recommend a professional roof check every few years to ensure optimal performance.
If you’d like us to inspect your GRP roof, reach out to your team, and we’ll arrange a convenient visit.
Does GRP Handle UK Weather Well?
Yes, and this is one of the key reasons it keeps growing in popularity.
GRP roofing resists:
- Heavy rain
- UV damage
- Temperature fluctuations
- Wind uplift (when correctly fixed)
The fully bonded system helps prevent water ingress, making it a strong contender among modern flat roof solutions. The watertight nature of GRP roofing ensures long-term protection against leaks, even in challenging UK weather conditions.
Is GRP Roofing Right for You?
GRP is an excellent option if you:
- Want a seamless waterproof system
- Prefer a modern appearance
- Need durability for balconies or walkways
- Are replacing ageing felt roofing
- Have complex roof detailing
It may be less suitable if your building experiences significant structural movement, in which case, we may recommend alternative flat roof solutions.
At AL King Roofing Ltd, we always carry out a full assessment before recommending any system.
Why Choose AL King Roofing Ltd for GRP Roofing?
Choosing the right material is important, but choosing the right installer is critical. AL King Roofing Ltd offers complete, engineered GRP roofing kits designed for both contractors and DIY installers, ensuring a straightforward and reliable installation process.
Our team ensures:
- Proper roof deck preparation
- Supply of high-quality roofing kits with all necessary components for a complete installation.
- Correct resin application
- Accurate curing times
- Secure edge detailing
- Thorough quality checks
Professional installation is what ensures your GRP roofing delivers long-term performance.
If you’re planning a flat roof project, contact us for expert advice and a no-obligation quotation.
Is GRP Roofing Worth It?
GRP roofing continues to grow because it delivers:
- Strong, seamless waterproofing
- Long lifespan
- Modern aesthetics
- Versatility across roof types
- Low maintenance requirements
GRP’s durability and waterproofing have been proven in the marine industry, where it is widely used for boat and yacht construction.
Like all roofing systems, it must be installed correctly and maintained sensibly. But when done properly, it offers one of the most reliable flat roof solutions available today.
If you’re considering upgrading your roof, call our team or get in touch to discuss your project with our experienced team.
FAQs About GRP Roofing
How long does GRP roofing last?
Typically, 25–40 years or more when professionally installed and maintained.
Is GRP roofing fully waterproof?
Yes. A properly installed waterproof GRP membrane creates a seamless barrier against water ingress.
Can GRP roofing be walked on?
Yes, with a suitable non-slip finish, it’s ideal for balconies and walkways.
Is glass reinforced roofing better than felt?
GRP generally offers greater durability, fewer seams and longer lifespan than traditional felt systems.
Does GRP require much maintenance?
No. Occasional inspections and clearing of debris are usually sufficient.