A GRP flat roof, or fiberglass roof as it’s also known, is one of the most popular flat roofing solutions in the UK. GRP stands for Glass Reinforced Polyester, a composite material formed by strengthening plastic with fine fibres made of glass.
This single ply laminate has been used as a reliable means of covering and waterproofing roofs for over 60 years, although it's popularity has soared in recent years thanks to new systems such as Cromar PROGRP. As well as commercial and domestic buildings, GRP has been used on a wide array of other applications, from boats and lorries to water tanks and ponds.
The installation of a GRP roofing system is highly regarded for its simplicity and safety, while the finished product it produces is recognised as having a lifespan that easily betters that of a felt roof.
GRP flat roofs begin with a layer of catalysed resin being applied to good quality, completely dry roof decking, ideally OSB3 wood. A layer of fibreglass mating is then laid on top followed by another layer of catalysed resin to complete the system. Once cured, a fire retardant top coat resin is then applied to completely weatherproof the roof and give it a more attractive finish.
Specially made edge trims and drip trims are fitted to the edges of the roof and abutments before any GRP is laid down
If installed correctly and sensibly looked after, there is no reason a GRP flat roof can not last for at least 30 years without any measurable deterioration.
See our PROGRP installation guide for in-depth instruction. The guide covers GRP installation on both cold roofs and warm roofs.
How Much Does a Fibreglass Roof Cost?
Needless to say, the overall cost of any GRP roofing system will depend on whether a new roof is being constructed or an existing roof is being repaired/altered. The latter will of course be vastly cheaper.
Naturally, the surface area of the roof and whether you need to bring in the professionals for installation, will need to be considered when budgeting for your GRP roof.
You’ll also need to think about if any structural repairs need to be carried out on the roof and if alterations are required to the guttering or downpipes.
Given the greatly superior durability of GRP roofing to felt systems, you might think that a GRP flat roof would cost a great deal more. This is not the case.
Although GRP is pricier than felt or EPDM rubber roofing systems, when you factor in this impressive longevity, along with the lack of maintenance needed, resistance to all weather and attractive laminated finish, fibreglass roofs can be worth every penny.
You can expect to pay between £70-£90 per square metre for a GRP roof, although this price can go up or down depending on location. The majority of roofers and roofing firms will include reboarding in their fee. A DIY installation will of course be substantially cheaper, however should this go wrong your guarantee will be voided with many manufacturers.
What About a Fibreglass Roof Repair?
Repairs are not something you’d associate with a GRP flat roof. As long as the original job was carried out correctly on suitable decking with properly installed trims and flashing, your GRP roofing system need little cause for concern.
Although impact resistant, should your fibreglass roof somehow develop a split or hole, there is nothing to stop another round of GRP being laid on top as long as the roof is still structurally sound.
Fibreglass roofs are unaffected by UV but fading can occur over the years. This will only affect the aesthetical quality of the roof, nothing internally. Should you want, any loss of colour can be combated by applying another layer of top coat to restore your GRP roof to its original glory.
If your GRP roof is leaking, a problem not normally linked to GRP, it may well be as a result of poor workmanship. Check that the flashings are installed properly and all trims are fitted correctly as this could be the likely cause of the leak.
What GRP Roofing Supplies are Needed?
GRP resin, catalyst/hardener, fibreglass mating and a top coat resin are the essentials of a GRP roofing system, along with the fibreglass roof trims and flashing.
In addition to these materials, a GRP shopping list also needs to include sealants and adhesives to bond trims and flashings, along with rollers, brushes and buckets.
With the exception of the trims and flashing, everything needed for a perfect GRP flat roof installation can be purchased as part of the all-in-one GRP kit from Cromar.
Your PROGRP roofing kit can be purchased at Roofinglines for delivery in one working day to help keep overall costs down or purchased as individual items should you only need to restock on a particular material.
Other inexpensive materials to consider include corners, to enhance the look around the roof, and an anti-slip feature such as Cromar Scangrit or slate chippings.
How Does GRP Compare to Other Flat Roof Coverings?
Although pricier on average, GRP roofs come with a number of advantages on a level that few other flat roofing solutions can offer.
As well as being more durable than traditional felt systems like pour-on or torch-on, GRP fibreglass is also a lot safer a solution. The chances of an on-site injury occuring are significantly less with fibreglass flat roof systems as it does not require any open flame or any other complicated or hazardous tools.
Other practical features of fibreglass flat roofs include there being no joints or seams on the main part of the roof. This means no taping and less chance of water creeping through gaps and into the decking. GRP offers the complete waterproof solution, the reason it's commonly used on boats and yachts.
The top coat finish in a GRP roofing system makes the roof resistant to pretty much all that nature can throw at it. Fibreglass roofs are built to retain their form and function in the face of storms, snow and frost and long periods of excess sunshine. GRP is also resistant to fire and can cope with footfall, making it suitable for a roof terrace.
Another edge GRP flat roofs have over bitumen roofs is the ease of maintenance that’s involved. Simply give the roof a brush and hose down every so often to keep it looking in top condition and protecting your home as it should.
A flexibility to be easily shaped to fit the design of any roof design is another string to the GRP bow and a reason why it is viewed by so many as the ideal flat roof covering and slightly more expensive than alternative options.
Although EPDM is another outstanding roof covering system, some people do not like the rubber roof look that comes with it. The finish which the top coat resin gives GRP roofs is generally considered far more pleasing on the eye. The top coat can be purchased in a variety of different colours to give the roof some added personality, although a traditional dark grey finish is still most popular.
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