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GRP Roofing (Fibreglass Roof)


We provide a full range of GRP roofing services. This includes GRP flat roofing and fibreglass roof repairs. Our highly-experienced team covers all of London and the South of England, and are fully accredited roofers.

If you would like a quotation or any information on GRP Roofing please get in touch with us or call us now on 01277 375 511.

What is a Fibreglass Roofing System?

A Fibreglass (GRP) Roofing system is a seamless flat roofing system which has been in use for over 30 years.

It can be applied to virtually any roof build up. This includes sloped roofs, dormers, parapet wall details and mansards. Some GRP systems can even be used as an overlay system with the correct primer.

A UV Protection coating can be applied to the system. Modern systems such as Polyroof now make GRP Roofing an even more attractive choice as a roofing system. These systems benefit from being self terminating, having built in UV protection and the ability to cope with complex detailing.

GRP Flat Roofing has become a very popular method of roofing in the UK of the past 20 years or so due to the slick, polished look it gives as well as the fact it is easy to maintain. It is a fully integrated continuous system where all the components are designed to work in unison.

GRP stands for Glass Reinforced Polyester which is a composite material that is made by using fine fibres of glass to strengthen plastic. The method and materials used in the making of this roof have led to it often being referred to as either ‘GRP Flat Roof’ or ‘Fibreglass Flat Roof'.

Below we explore Fibreglass roofing in detail; we will look at how it is laid, the different durability options available, how cost is calculated, how to maintain your GRP Flat Roof and the potential problems that occur with fibreglass roofing.

The Benefits of GRP (Fibreglass) Flat Roofing Systems

• Fibreglass flat roofing systems are BBA Certified. This means it is a roofing system which has passed a rigorous testing process.

• They are excellent waterproofing solutions for all types of domestic and commercial properties.

• GRP Roofing Systems come with product and workmanship guarantees of up to 40 years.

• Proven performance with over a million square metres fitted over the last 20 years.

• One of the most versatile flat roof materials which can be used in a range of situations including: new build, replacement roofs, listed or iconic buildings.

• Environmentally sustainable by design and safe to install.

• No heat required.

• Rated A/A+ in the generic BRE Green Guide1.

• Fire Retardant and completely UV resistant

• Over 1,000 different combinations of colours, and specialist finishes available.

• Highly Rigid Roofing System

• Systems such as Ultraflex can cope with Irregular Shapes and have Superior Flexibility compared to other GRP Roofing Systems.

• Ideal for Roof Gardens (Brown and Green Roofs) as are anti-root and all joints are seamless.

How Versatile is Fibreglass Flat Roofing?

GRP flat roofing is an extremely versatile roofing system that can be applied to almost any type of roof build up. They are also suitable for vertical detailing like attics, dormers, sloped roofs or parapet walls. Further to this, its robustness makes it suitable to be used for pavements and balconies. It is also a roofing system that comes with a BBA certification- to achieve this certificate roofs have to go through a rigorous testing process.

Fibreglass roofing can also be used to roof water contaminants that can sometimes be found on roof gardens. They are versatile enough to be used on mud roofs or grass roofs and give a completely seamless finish.

Fibreglass manufactures will have different specifications for their build up systems, with the right primer come can be used as an overlay system that can be put onto customers current roofing systems including mastic asphalt, RBA felt and concrete. In these circumstance with the added details of flashing and wall reinforcement the system looks very appealing.

GRP Flat Roofs are easy to maintain?

The best way to clean and maintain a GRP Flat roof is by using soap and water, alternatively you could use a brush to sweep it clean or a low-pressure jet wash.

What Is The Cost Of A GRP Roof

One of the reasons fibreglass roofing is so popular is because of it is both looks appealing and is also extremely durable. GRP Flat roof construction is an effective, simple and safe method of roofing that comes with a lengthy guarantee.

There are many factors influencing the cost of a fibre glass roof, for example the size of the roof, the roof specifications, the volume of build-up and whether the roof requires any finishing touches. The easiest way to understand how these factors affect pricing is my exploring how a fibreglass roof is constructed.

So how is a GRP Flat roof constructed?

The Process for a New Build Roof with a 15-20 Year Guarantee:

The first step is to install a 18mm OSB Board onto the rafters of the roof or to the current roof surface if re-roofing.

Once this is done trims and flashing will be installed and depending on whether the OSB board is T and G or not a strap will need to be secured over every other board joint.

Now the roofers will use a 2part resin/450g matting (CSM) with a topcoat UV to cover the roof. The costing for this would be about £65 to £90 per square meter depending on how large the area is being covered.

Another fact to consider whilst calculating the cost of a fibreglass roof is whether the roof has any insulation. If your roof doesn’t have any insulation the roofs build up changes. It will need to have a 9mm sub-deck followed by a VCL (vapour control check layer), depending on the specification the roof will need counter battens to aid air flow and then a 120mm insulation rigid. The overall cost for a roof build-up is between £45- £60 per square metre.

Looking at the cost from beam to roof finish (minus any soffits, fascia or gutters) the typical cost of for fibreglass flat roofs is between £110 - £150 per square metre.

It is worth noting that if you choose a more complex detailing or add specialist finishes on certain areas, for example a balcony, the cost will increase.

A Longer Guarantee Will Increase The Price Of The Roof

If you decide to opt for a longer life guarantee for roof this will in turn increase the price. For example, if you decide to choose a 30-year roof guarantee this will mean the roofers will apply an extra coat of resin over the three part build up. The price of this additional coating will cost between £10 to £15 per square metre.

As mentioned above you may want extra detailing or specialist finishes on areas of your roof, which again will affect the pricing. If you wanted to add balcony detailing roofers will need to use a higher-grade chop stranded matting that is embedded into the resin, to allow for the foot fall this part of the roof will endure.

What is chop stranded matting (CSM)?

It is a traction coating that is typically 650g thicker than standard CSM2. It has to be thicker as more resin is need to be soaked in by the matting. The higher grade CSM is then left to cure before a UV protection layer is added and finally traction chippings are spread over the wet area.

Sometimes once the roofing area has dried it may be that it needs an additional UV protection layer added, this would be an additional cost of £8-15 per square meter.

How is the process different with a 40-year guarantee?

If you are looking for a 40-year guarantee on your Fibreglass roof the process explored above will require an extra three layers. These layers consist of a further layer of resin followed by a CSM layer in the middle and a final layer of resin.

The cost of these extra layers is between £12- £20 per square metre added to the cost for a 20-25-year GRP flat roofing system price.

Other additional costs for GRP Flat Roofing on Roofs with a Longer Guarantee:

Other additional cost that come with longer guarantees is the cost for cleaning or stripping of any pre-existing waterproof coverings. The cost of cleaning and stripping is normally around £7 to £15 per square meter for each water proof later. Of course, other things will factor in such as the access to the roof when any debris is removed from area.

Looking at the costing for a GRP Flat Roof in comparison to other roofing systems, and from the point of view of cost per year guarantee, I feel it proves itself to be a very competitive roof installation within the roofing market.

Further costing help:

Should you want to investigate fibreglass roofing costs further on a square meter basis please do have a look at our GRP Roofing Cost Calculator as this can really help you with working out a price for your roof.

Summary of key factors that influence the pricing of a Fibreglass Flat Roof:

So, to summarise the key elements that will impact the price of a Fibreglass Flat Roof are:

• The size of your roof

• The specification you are going for.

• The level of build-up you require.

• The complexity of your installation.

• The length of guarantee you require.

Potential Fibreglass Roofing Problems

Whilst fibreglass roofing is a fantastic option at times it can face some issues. Our blog post on fibreglass roofing problems looks at this in detail. These include roof cracking, alligatoring, pin holes, leaking, guttering and noise issues. So, let’s identify what these issues look like, why these problems occur and how they can be dealt with.

GRP Roof Cracking

Unfortunately, cracking is often caused by poor roof installation. Cracking is easy to identify and looks like flaking and peeling of the roof’s top surface.

But What Causes Fibreglass roofs to crack?

In warmer months the heat of the sun causes the GRP roof to heat and expand, then as the sun sets and the temperature drops the roof contracts back to its original size. The repetition of these movement of the roofs surface causes the Fibreglass roofing to crack over time. The term given to this process is thermal expansion.

How can cracking on a GRP Roof be rectified?

Once the damaged area of the roof has been identified the best solution is to replace this area. Roofers do this by cutting out the area affected by the cracking and then replace it with new fibreglass, resin and the protective top coat. It is, of course, essential that it is correctly installed this time so that the problem doesn’t reoccur. The best way to ensure it is done properly is by using an accredited GRP roofing company.

Fibreglass Surface Alligatoring

Once A GRP roofing system reaches the end of its lifetime it begins to lose its elasticity, this makes its appearance change and look cracked and wrinkled just like the skin of an alligator, which is where the term ‘alligatoring’ comes from. Sadly, if your roof has reached this stage there is no available solution and it will have to be completely replaced.

Pinholes on the Surface Of The Flat Roof

What is a Pinhole?

It can be difficult to identify pinholes on a GRP roof without getting up on your roof and inspecting it closely. Pinholes are literally tiny holes across the surface of the roof, which is were the terminology ‘pinholes’ comes from.

What Causes Pinholes?

Unfortunately, pinholes most commonly occur when not enough top coat is applied to the roofs surface during installation.

Why are pinholes a Problem?

On first inspection these pinholes may appear harmless because of how small they are, however they tend to lead to water ingress following heavy rain and high winds. The pooling of this water can then lead to water leaking through the pinholes on a GRP roof and damage the contents below.

Can they be fixed?

Yes, there is an effective way to solve the issue of pin-holing on a GRP flat roof. A fresh coat of resin can be applied to the area suffering from pinholes, this will then seal the tiny holes and prevent any of the issues discussed above from occurring.

Ponding on a Fibreglass Roof

What is Ponding?

As the name suggest ponging is when large pools of water congregate on a flat roof. If ponding occurs it places the roof at risk of leaking. Whilst it can be hard to spot whether there have been large pools of water on your flat roof there are other tell-tale signs you can lookout for, such as lighter or darker patches on your roof compared to the roofs original colour or what looks like rings wait a dirt stain around them.

Can Ponding be rectified?

Should you notice ponding on your roof it is best to contact a Fibreglass roof specialist immediately. The only way to rectify this issue is to board the roof with firings as at this point applying another layer of GRP coating is not an option.

Fibreglass Roof Suffering From Leaks

What causes a roof to leak?

When a roof cracks water begins to pool in these areas making water ingresses. Unfortunately, cracks appear when a roof has not properly been installed. Cracks in the surface of the roof will lead to water ingress, these cracks are created if the roof has not been installed properly.

Can leaks be fixed?

Firstly, you need to identify where your leak is and the best way to do this is by going up onto the roof. You need to look for any cracks or pinholes, described above, as this will confirm where the leak is. After identifying your leak, the surveyor will follow a three-step plan of action; they will sand down the area, add a resin coat and final apply the topcoat (which will be a colour match to your roof’s original colour).

Damaged Or Blocked Guttering

It is important to maintain your GRP Flat roof and give special attention to your guttering as they are known to become blocked so need to be checked regularly and cleaned. The risk of blockages in the gutter can be reduced by sweeping your roof clear of any leaves, dirt or debris that may have built up as this will prevent the rubble from any rainfall to pool and create water ingresses - which could then lead to leaking.

If your find that even with regularly clearing your gutters and sweeping your roof you are struggling for your own peace of mind it is worth contacting a roofing professional to come and evaluate whether you need a new guttering system fitted to your fibreglass roof.

Noise Problems with a GRP Flat Roof

Sometimes customers can report that they can hear creaking or cracking come from their fibreglass roof.

What causes these sounds?

These sounds could be caused by the change in temperature in the warmer months- as explored above thermal expansion can cause problems for GRP Flat roof systems, as when the roof heats and expands on a warm day and then cools in the evening the roof creaks as it contracts back to its original shape.

How to rectify this issue:

This is a normal process that is expected and steps can be take to reduce the negative side effects the expanding and contracting of the roof can cause. Roofers can use special expansion joints when installing a roof which help the flexibility of the fibreglass and reduce any noises the expanding and contracting process makes.

The Key Ways To Prevent GRP Flat Roofing Issues

GRP roofing is an excellent flat roofing system and the issues we have discussed above will only happen for the following reasons:

• The GRP roof has reached the end of its life span.

• It hasn’t been properly maintained.

• The roof was not correctly fitted.

The best way to reduce the chances of these problems occurring is by ensuring you use a reputable Fibreglass specialist to install your roof.  In addition to this it is important to regularly maintain your roof, e.g. cleaning the gutter, sweeping the roof cleaning and carrying out regular inspections to evaluate your roof’s health.

Why Choose RJ Evans For GRP Roofing

• Experienced team of fully accredited GRP Roofing Specialists. We have operatives with more than 40 years’ experience.

• We provide a range of FREE quotations and solutions for all projects.

• Insurance Backed Guarantees.

• Excellent Customer Support throughout project.

• Rated 5 out of 5 by our previous customers.

Get In Touch With RJ Evans Today

If you would like a quotation or any information on a fibreglass flat roof installation, survey or repair please get in touch with us through our contact form or call us now on 01277 375 511. One of our friendly team will be delighted to help you.