Leeds & District Roofing Blog

Are Grp Roofs a good idea

Updated: Jul 30

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

It's our view that Cureit GRP products are the best on the market.

For many years, we have been authorised installers of the Cure It GRP waterproofing system.

To get a free estimate for all of your flat-roofing requirements, please contact us today

Are grp roofs expensive

When fitting a grp roof in Leeds, grp is one of the most expensive product on the market for flat roofs. But i would always recommend a grp flat roof to our customers as flat roofs can be problimatic and with 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 amazing 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 Rpoof - £110.00 SQM

The prices quoted above are for fully stripping off your old roof and disposing of the waste, adding new osb-3 tung and groove boards and then which ever surface you want applying.

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 a less amount of material is needed to provide the same level of strength. GRP, on the other hand, has a number of unique qualities that allow it to be moulded 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 leak. If you have a tiled roof, you may only utilise a velux flashing kit with a 15-degree slope. 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 maximise 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 benifit to a flat roof window is these windows can open. Velux do a solar and electric flat roof window, which can add extra venilation 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 which window will you get the most benifit 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 fibreglass roof.

Glass Reinforced Polyester (GRP) is a composite material manufactured by combining plastic and glass fibres.

While this single ply laminate has been used to cover and waterproof roofs for over 60 years, its popularity has recently skyrocketed because to the introduction of innovative solutions like Cureit.

GRP has been utilised for anything from boats and trucks to water tanks and ponds, as well as 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 catalysed 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. With all new roofs you have got to upgrade the thermal value of the roof so an inspection of the insulation is needed. We find iko enertherm to be the best insulation on the market to use, but you can choose which ever insulation you like using.

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

Replacing a grp roof
Poor Insulation
Good insulation

What boards do you use on grp roofs

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

Almost little delamination will occur because to the board's rough texture, which provides a good grip for the resin and helps it 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 galvanised 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 centre, 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 leant 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 bandage for sealing all trims to new roof deck.

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

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

6. Prepare tools, i.e. application rollers (3” + 7”) metal laminating rollers (3” + 7”) laminating brushes, 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 litres) 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 shorter working time (more catalyst)

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


Beginning at the highest edge of the roof, apply the catalysed resin to 1m2 of roof. (To achieve the correct ratio of resin to CSM, approximately 1⁄3 needs to be applied to the deck and 2⁄3 on to the mat). Lay the leading edge of one of the strips of mat you cut earlier into the resin and unroll the first square metre. Impregnate the mat you have unrolled before continuing to repeat the process along the length of the strip of mat. When laminating the main roof area, never mix more than 10litre 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 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 catalysed resin to the affected areas. To make overlapped areas less prominent tear matting, this 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 catalyst to resin, always mix well to ensure even distribution. One minutes 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 topcoated. 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 fibres 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 topcoating the main area and after you have cut in with topcoat, sealing in place using cromar trim adhesive. Remember to include a bead of PU adhesive between the angle fillet and 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 1minute. 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 fibre 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 a grit or slate chip pings can be sprinkled onto the topcoat. This needs to be added by hand or a dispensing applicator as the roof is topcoated. It can be left uncoated to give a ‘mineral’ finish or re-coated with 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, 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 application of ProGRP of 35degrees centigrade, to reduce this problem, cover the roof as 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.

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