top of page

Are GRP Roofs a Good Idea

Updated: Aug 14, 2023

Glass-reinforced plastic (GRP) roofing is the best option for flat roofs (also known as fiberglass roofs).

No repairs have ever been needed on these roofs that we've installed over the last 45 years. These roofs come with a 20-year guarantee, but if correctly built, they may endure up to 40-50 years.

We believe Cureit GRP products are the best on the market.

We have been authorized installers of the Cure It GRP waterproofing system for many years.

Please contact us today to get a free estimate for all your flat-roofing requirements.

GRP (Glass-Reinforced Plastic) flat roofs can be a good option for certain situations, but whether they are a good idea or not depends on various factors. Here are some considerations:

1. Durability: GRP roofs are known for their durability and longevity. They have good resistance to weathering, UV radiation, and general wear and tear. This can make them a suitable choice for flat roofs that are exposed to harsh environmental conditions.

2. Waterproofing: GRP roofs are seamless, meaning they have no joints or seams where water can penetrate. This can provide excellent waterproofing properties and help prevent leaks. However, proper installation is crucial to ensure a watertight seal.

3. Maintenance: GRP roofs require minimal maintenance. They are relatively easy to clean and can withstand foot traffic without being damaged. Regular inspections and occasional cleaning are usually sufficient to keep them in good condition.

4. Installation: Proper installation is essential for the performance and longevity of a GRP roof. It typically involves laying multiple layers of resin and fiberglass matting onto a prepared surface. If not installed correctly, issues such as delamination or inadequate adhesion may occur.

5. Cost: The cost of GRP flat roofs can vary depending on factors such as roof size, complexity, and location. While the initial installation cost may be higher compared to some other roofing materials, the long-term durability and low maintenance requirements can make them cost-effective over time.

6. Expertise: Installing a GRP roof requires specific knowledge and skills. It's recommended to hire a professional roofing contractor experienced in working with GRP systems to ensure proper installation and avoid potential issues.

Ultimately, whether a GRP flat roof is a good idea depends on your specific needs, budget, and the expertise available for installation. It's advisable to consult with a roofing professional who can assess your requirements and provide personalized recommendations.

Are GRP Roofs Expensive

When fitting a grp roof in Leeds, grp is one of the most expensive products on the market for flat roofs. But I would always recommend a grp flat roof to our customers as flat roofs can be problematic, and a GRP Roof, it will solve all your flat roof issues. A bonus to fitting a grp roof to your home is the finish looks fantastic, and out of all the flat roof products, grp has the best finish.

What is the average price for a GRP Roof

Grp roof - £135.00 SQM

Felt roof - £100.00 SQM

EPDM Roof - £110.00 SQM

The prices quoted above are for entirely stripping off your old roof and disposing of the waste, adding new OSB-3 tung and groove boards, and then whichever surface you want to apply.

What are the benefits of a GRP Roof?

The remarkable strength-to-weight ratio of GRP roofing is only one of its many advantages.

This implies that less material is needed to provide the same level of strength. On the other hand, GRP has several unique qualities that allow it to be molded to practically any form, including odd roof shapes and uneven buildings.

Can I add a window for light to my flat roof?

Yes there is a number of roof windows that can be added to your flat roof

  • Velux window

  • Roof window

  • Roof lantern

Velux windows

Over the years, we've seen a lot of low-pitched roofs where the incorrect tile was used on the extension roof, causing major leaks.

It's usually a good idea to add a grp roof to your house expansion if you plan on installing Velux windows and end up with a roof pitch of 12 to 15 degrees.

It has been my experience that whatever tile you lay on a low-pitched roof will begin to leak within ten years. In the event of a severe downpour, Velux windows on a low pitch roof may inform. You may only utilize a Velux flashing kit with a 15-degree slope if you have a tiled roof. For many years, our firm is the only one that can successfully install and maintain Velux windows on a low-pitched roof.

Roof Lantern

It is possible to install roof lanterns on any flat roof and reap the benefits.

Lighting at the rear of a room is diminished when a new extension is built.

To maximize the amount of natural light entering the new addition, consider installing a roof lantern on the flat roof.

There is a cost difference between roof lanterns and Velux windows, but they are an excellent solution for a flat roof.

Flat Roof Window

The added benefit to a flat roof window is these windows can open. Velux do a solar and electric flat roof window, which can add extra ventilation to your home. Out of all these windows, these are the most expensive, but when adding a window to your flat roof, the number one thing you should consider is which window you will get the most benefit from.

When it comes to flat roofing, one of the most common options in the UK is a GRP flat roof, commonly known as a fiberglass roof.

Glass Reinforced Polyester (GRP) is a composite material manufactured by combining plastic and glass fibers. While this single-ply laminate has been used to cover and waterproof roofs for over 60 years, its popularity has recently skyrocketed because of the introduction of innovative solutions like Cureit.

GRP has been utilized for anything from boats and trucks to water tanks and ponds, and commercial and residential structures. The GRP roofing system is admired for its longevity and durability, and its installation is praised for its ease and safety.

Catalyzed resin is first put on high-quality, totally dry roof decking, preferably OSB3 wood, to begin the process of installing a GRP flat roof. To finish the system, a coating of fibreglass mating is applied, followed by a layer of catalyzed resin. The roof is then weatherproofed and given a more aesthetically pleasing finish by applying a fire-retardant top coat resin after it has hardened.

How are GRP Roofs fitted?


With all new flat roofs, we always start off by removing the old flat roof. However, with all new ceilings you have got to upgrade the roof's thermal value, so an insulation inspection is needed. We find Northern to be the best insulation on the market, but you can choose whichever insulation you like.

If the insulation is up to standard, you can move on to the next step, but if there is no insulation or the insulation is not up to regulation, you will need to upgrade it. To prevent condensation from forming when the insulation is placed at ceiling level, a minimum of 50mm gap is provided for ventilation above the insulation.

What boards do you use on grp roofs?

A new fiberglass roof is best installed on a roof deck made of oriented strand board, namely OSB3 Tongue & Groove.

Little delamination will occur because of the board's rough texture, which provides a good grip for the resin and helps its key into the board. We have tried other boards, but for the best finish, these sterling boards should be used.

How do I add the GRP trims

Use 15mm galvanized clout nails to secure the trims to the decking board.

While holding the trim in place and checking that the face is level, you may begin fastening the ends, the center, and the remaining 200mm.

To attach the trims, just apply a bead of PU glue to one surface and allow the pieces to overlap by at least 50 mm.

If a ladder will be regularly leaned against the trim for roof access or window cleaning, it is recommended to either double up by slotting in an additional piece of trim where the ladder would go or reinforcing with an extra layer of GRP laminate and then surface tissue to retain the smooth finish.

How do I apply the GRP resin?

1. Ensure all debris, tools, etc. are removed from the roof and the roof is swept clean and obviously is completely dry.

2. Cut the matting mat for detailing work.

3. Prepare a bandage for sealing all trims to the new roof deck.

4. Roll out and cut the mat for the whole roof surface (remembering 50mm overlap)

5. Roll up strips of the mat and place them together. Lay out the first strip of the mat along the highest point and continue overlapping each strip by 50 mm

6. Prepare tools, i.e. application rollers (3” + 7”) metal laminating rollers (3” + 7”) laminating brushes, and mixing buckets.

7. Select an area on the ground, adjacent to the ladder for mixing. Protect the mixing area from spills or splashes using either an off-cut of decking or a plastic sheet.

8. Mix a small batch (1-2 liters) for detailing and bandaging. This is an ideal opportunity for assessing the quantity of catalyst you are using and whether you need a longer working time (less catalyst) or a shorter working time (more catalyst)

9. Mix and apply resin and chop strand mat for the roof area to be laminated


Beginning at the highest edge of the roof, apply the catalyzed resin to 1m2 of the roof. (To achieve the correct ratio of resin to CSM, approximately 1⁄3 needs to be applied to the deck and 2⁄3 onto the mat). Lay the leading edge of one of the strips of mat you cut earlier into the resin and unroll the first square meter. Impregnate the mat you have unrolled before continuing to repeat the process along the length of the strip of the mat. When laminating the main roof area, never mix more than 10 liters at a time, even less in warm weather. This will ensure that you DO NOT risk the basecoat resin going ‘off’ in the bucket and becoming unusable.


After the first 2m of the mat has been laid and impregnated, the laminating roller (bubble buster)is used to evenly distribute the resin across the mat and help move any air pockets. Using the laminating roller, apply light pressure to the wetted mat using long even strokes, making sure that the whole area of the mat is worked until transparent. Any area that is white or opaque will require more resin applied. Continue until the whole flat area of the roof is laminated and consolidated. The mat is properly ‘wetted out’ when it appears almost transparent i.e. you can clearly see the decking below. Remember to work towards an area where you can get off the roof. Repeat this process until the whole roof is laminated

When laminate is complete and cured, inspect for ‘pinholes’, If found, apply a further light coat of catalyzed resin to the affected areas. To make overlapped areas less prominent tear matting produces a feathered edge which softens the joins. Always mix the resins on a clean area, a sheet, or a board adjacent to the ladder. When leaving the roof always inspect the soles of your boots To avoid resin being ‘walked’ onto your customers’ property. When adding a catalyst to resin, always mix well to ensure even distribution. One minute of stirring is recommended. Never mix too large a quantity. You can always mix more – you can never put it back if you have mixed too much.


Before applying ProGRP Topcoat it will be necessary to lightly sand the whole of the roof surface, corners, and details. A smooth, unblemished surface will produce a high-quality finish when top-coated. After the roof has been sanded an Acetone wipe will greatly aid the adhesion of the final topcoat. Using a sanding pad or sandpaper (40-60 grit) lightly sand the corners, taking care not to create ‘holes’. Any unsightly fibers can be trimmed off using a safety knife. If a hole in the laminate is found this should be filled with catalysed resin before proceeding. If the roof requires the use of C100 cover flashing trims, these should be fitted prior to top coating the main area and after you have cut in with topcoat, sealing in place using Cromer trim adhesive. Remember to include a bead of PU adhesive between the angle fillet and the inside of the flashing trim


Calculate the amount of topcoat required, measure out into a bucket, and add Catalyst to each batch of topcoat as you need it. Stir well for at least 1 minute. To calculate the amount of topcoat required see the ready reckoner supplied by Cromar. Apply to the roof surface starting at the furthest point from the exit point on the roof and using the relevant sized soft application roller. The coat applied should allow the fiber pattern of the laminate to still be visible after application. If applied too thickly, the topcoat may crack over a period of time. Using long smooth strokes, apply the topcoat to the laminated roof surface, finishing at the point of exit. If a non-slip finish is requested grit or slate chippings can be sprinkled onto the topcoat. This needs to be added by hand or a dispensing applicator as the roof is top-coated. It can be left uncoated to give a ‘mineral’ finish or re-coated with a topcoat to give a textured finish. For a neat finish use masking tape or batons to define the edges of the aggregated areas. When the topcoat has fully cured “grabbing” the aggregate, sweep off any excess. Mixing buckets can be re-used. To clean tools, use acetone in a re-sealable container. It is advisable to use paintbrushes with unpainted handles as the paint will contaminate the resin. Always use disposable latex gloves when handling resins and topcoat, and use hand cleaner or wipes to clean off resin or topcoat.


On a hot sunny day, the roof deck can reach very high temperatures before you even begin laminating. This in turn means the decking can exceed the recommended upper temperature limit for the application of ProGRP of 35degrees centigrade, to reduce this problem, cover the roof as the decking progresses, removing the covers only at the last minute.


Always check the local weather forecast. DO NOT apply resins to wet or frozen boards, if you ignore this advice the ProGRP will de-laminate. DO NOT apply below minimum temperatures i.e. 5o C Keep a waterproof sheet handy to cover the roof in case of rain.

Ask your question

  • What is the best flat roof product

  • Grp

  • Epdm

  • Single ply

Should I get a Fiberglass roof

GRP (Glass Reinforced Plastic) flat roofs can be a good option for certain situations. Here are some factors to consider when evaluating whether a GRP flat roof is a good idea: 1. Durability: GRP roofs are known for their durability and resistance to weathering, UV radiation, and temperature fluctuations. They have a long lifespan and require minimal maintenance. 2. Waterproofing: GRP roofs provide excellent waterproofing when properly installed. They consist of multiple layers of resin and fiberglass, forming a seamless and watertight surface. 3. Versatility: GRP roofs can be applied to various types of flat roofs, including extensions, garages, balconies, and commercial buildings. They can be customized to fit any shape or size, making them versatile in terms of design options. 4. Installation: GRP roofs are lightweight, which makes them relatively easy to install. They can be installed with minimal disruption, and the installation process is usually quicker compared to other flat roofing systems. 5. Aesthetics: GRP roofs offer a smooth, seamless finish that can enhance the appearance of a building. They can be finished in different colors and can incorporate non-slip coatings if required. 6. Cost: The cost of a GRP flat roof can vary depending on factors such as size, complexity, and location. While the initial installation cost may be higher than some other roofing options, the long-term durability and low maintenance requirements can make it a cost-effective choice over the lifespan of the roof. It's important to note that proper installation is crucial for the success of any roofing system, including GRP roofs. It's recommended to hire a professional roofing contractor experienced in installing GRP roofs to ensure the best results. Ultimately, whether a GRP flat roof is a good idea depends on your specific needs, budget, and the advice of a qualified professional who can assess your situation and recommend the most suitable roofing solution for you.

How long do Fiberglass roofs last?

GRP flat roofs have a reputation for being long-lasting and durable. When properly installed and maintained, a GRP flat roof can have a lifespan of 25 to 30 years or more. However, it's important to note that the actual lifespan can vary depending on several factors: 1. Installation quality: Proper installation is crucial for the longevity of a GRP flat roof. It should be installed by experienced professionals who follow manufacturer guidelines and best practices. 2. Maintenance: Regular maintenance, such as cleaning the surface and inspecting for any damage or wear, can help extend the lifespan of a GRP roof. Small issues can be addressed early on, preventing them from developing into major problems. 3. Environmental factors: The lifespan of a GRP flat roof can be influenced by environmental factors like exposure to sunlight, extreme temperatures, and severe weather conditions. UV radiation, in particular, can cause degradation over time. Applying UV-resistant topcoats can help mitigate this. 4. Foot traffic: If the roof is frequently accessed or subjected to heavy foot traffic, it can lead to premature wear and tear. Taking precautions, such as installing walkways or using protective mats, can help minimize damage. 5. Design and quality of materials: The quality of the GRP materials used in the roof's construction can affect its lifespan. Higher-quality materials and proper layering techniques can contribute to a longer-lasting roof. It's worth noting that regular inspections by a professional roofing contractor can help identify any issues or signs of deterioration early on, allowing for timely repairs or maintenance. This proactive approach can help maximize the lifespan of a GRP flat roof.

Recent Posts

See All


bottom of page