Why you should consider GRP Fibreglass for your flat roof

GRP is considered to be the best material for flat roofing systems. It’s strong, it’s lightweight, it’s maintenance-free and it can be patched. It’s 100% waterproof with no seams or glued joints for water to penetrate over time. It’s also strong enough and safe to walk on if the supporting roof can take the weight.

With so much going for it, it makes no wonder GRP is the recommended material for flat roofing. Nothing else comes close to matching its feature set.

There is a price to pay, of course. GRP fibreglass roofing is more expensive than asphalt, single ply and reinforced bitumen. However, there are plenty of reasons why the extra cost is worth it, which we’ll cover below.

Here’s why you should consider GRP Fibreglass for your flat roof:


GRP fibreglass offers unbeatable waterproofing performance. When installed correctly, it creates an impenetrable waterproof barrier. So, the material is 100% waterproof, and importantly it’s weatherproof too. No amount of wind, rain, snow or ice will damage GRP on its own. The only way it can be damaged is by impact.

No seams, no fuss

Felt roofing systems and even the most modern membrane roofing systems are fundamentally flawed because they have welded or glued seams. These are the weak point in a flat roof. GRP fibreglass has no seams or joints. It has a smooth, flat surface that cannot be penetrated even under high pressure.


GRP fibreglass roofing shouldn’t ever need repairing under normal circumstances. However, should your GRP fibreglass be damaged, for example by impact, the repair process is relatively simple. You just cut out the damaged area, sand it down, and replace the GRP with a patching kit. This will be bonded in with no detriment to performance.

Strength (for walking on)

Fibreglass layers are typically laid out in 450g, 600g or 900g layers to suit the predicted footfall. If you’ll be walking on your flat roof often, a 600g or 900g fibreglass layer is relevant to you. You can also use two layers of 450g fiberglass. Once installed, the fibreglass will back up the roof’s strength. Feel free to walk on it.

Low maintenance

The best roofing systems do their job and don’t ask you to think about them. GRP fibreglass is one of the best at this. It requires no maintenance whatsoever, unless it becomes damaged, shifts (for example, due to an earthquake) or needs cleaning. Most people don’t touch their fibreglass roof ever. They just forget about it.

Perfect for rooftop gardens

Because GRP fibreglass is impenetrable, it’s the best flat roofing material for rooftop gardens. If you plan to throw topsoil on there, drainage points will need to be installed but other than that GRP fibreglass is great for a rooftop garden. It’s also strong enough to support the weight of chairs, tables and pots.


GRP has a lifespan in excess of 30 years. Most branded fibreglass products come with a minimum 25-year guarantee, some up to 50 years. The important thing to remember about GRP is that it’s inert. It gets the job done and doesn’t degrade over time. Because of this, the long-term cost of GRP fibreglass is low.

It outlasts cheaper materials

You might be tempted to go with a felt and resin or asphalt flat roofing system to save a few hundred pounds right now. However, the reality is you’ll have to pay twice because cheaper systems degrade and will need replacing in time. GRP outlasts asphalt and felt by as much as 5 to 1, making it the best choice to save money long-term.

GRP is environmentally-friendly

There is no risk to the local environment during GRP installation. There are no harmful emissions or toxins used. Furthermore, GRP is inert – it doesn’t rot or deteriorate over time, so it won’t seep into any local water supply. If the right boarding is used, GRP roofs are also a Forestry Stewardship Council approved product.

Suitable for period homes

GRP fibreglass is also suitable for period homes, including Listed Buildings. Local planning authorities approve 8 out of 10 applications for GRP flat roofing to replace ageing felt, resin systems. If you have living in a Listed Building with a leaky flat roof, replacing it with a higher performance material like GRP fibreglass is acceptable.

Talk with us about GRP fibreglass roofing

Interested in GRP fiberglass roofing? Speak to our roofing experts for advice and a friendly chat. Call us on 0113 293 4038.

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