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GRP Roofing: What Is A Fibreglass Roof System?


GRP roofing refers to a roofing system where a liquid thermosetting polyester resin, reinforced with layers of glass fiber mats, is applied in its liquid state to create a seamless and waterproof roofing membrane. The resin cures and hardens after application, forming a durable, watertight, and weather-resistant roofing surface that provides protection against water infiltration and environmental elements. This system is often used for flat or low-slope roofs and is known for its longevity and performance in cold-applied roofing applications.


What is a Fibreglass Flat Roof System?

A fibreglass (GRP) flat roof 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 the benefits of a GRP flat roofing system, how it is laid, the different durability options available, how cost is calculated, how to maintain your GRP Flat Roof and the potential problems which occur with fibreglass roofing.

The Benefits of GRP (Fibreglass) Flat Roofing Systems

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

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

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

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

5. 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.

6. Environmentally sustainable by design and safe to install. Rated A/A+ in the generic BRE Green Guide.

7. No heat is required to install a fibreglass system.

8. Fire Retardant and completely UV resistant

9. A Complete Range Of Over 1,000 colours, and specialist finishes are available (dark grey is the most common GRP roof colour). 

10. Highly Rigid Roofing System

11. Hybrid GRP products can cope with Irregular Shapes and have Superior Flexibility compared to other systems.

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

These benefits show how fibreglass flat roofing is not only an excellent choice of roof but also one which provides a lot of versatility.

How Versatile is Fibreglass Flat Roofing?

Fibreglass flat roofing is extremely versatile and hard wearing. It can be used on a new roof, an old roof and 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 which 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 which 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 water tight 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.

No matter which system you choose for your GRP roofing system, it is important the correct maintenance is followed throughout the lifespan of the roof.

How Do You Mantain A GRP Fibreglass Roofing System

Maintaining a GRP (Glass Reinforced Polyester) liquid roofing system is essential for ensuring its longevity and effectiveness. Here are the key steps to maintain such a system:

1. Regular Inspections: Conduct routine inspections to check for any signs of damage, wear, or deterioration. Look for cracks, blisters, or areas where the membrane may have separated from the substrate.

2. Clean the Surface: Keep the roofing surface clean by removing dirt, debris, and standing water. Use a gentle detergent and a soft brush or mop to clean the surface without damaging the GRP membrane.

3. Address Repairs Promptly: If any damage or defects are identified during inspections, address them promptly. Small issues, such as cracks or punctures, can be repaired using compatible GRP roofing materials.

4. Periodic Re-Coating: Depending on the manufacturer's recommendations and the age of the roofing system, consider periodic re-coating to renew the protective layer and extend the system's lifespan.

By following these maintenance practices, property owners can ensure their GRP liquid roofing system remains in good condition, providing reliable waterproofing and protection against the elements. Doing this also greatly increase the return of investment you get from your GRP roof. It is important to note the cost of a GRP roof can play a significant part in your roofs longevity.

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.

GRP Flat Roof Construction Details

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 GRP edge  trims and flashing will be installed. 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 fibreglass 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 which is embedded into the resin, to allow for the foot fall this part of the roof will endure.

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 and £20 per square metre added to the cost for a 20-25-year GRP flat roofing system price.

Further Additional Costs For GRP Flat Roofs With a Longer Guarantee

Further additional costs which 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 waterproof layer. 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.

Should you want to investigate fibreglass roofing costs further on a per square meter basis please do have a look at our GRP Roofing Cost Calculator. This can give you a good guide on to what the cost of your roof would cost, should you choose GRP.

Key Factors Which 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:

1. The size of your roof

2. The specification you are going for.

3. The level of build-up you require.

4. The complexity of your installation.

5. The length of guarantee you require.

Get In Touch With RJ Evans Today

If you would like a quotation or any information on a fibreglass flat roof system 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 give you everything you need in order to make the correct decision for your project..

How Does GRP Compare To Other Flat Roofing Systems?

GRP (Glass Reinforced Plastic) roofing systems offer several advantages when compared to several other flat roofing systems:

1. Durability and Longevity: GRP roofing is known for its exceptional durability and longevity. It can withstand the test of time and is highly resistant to environmental factors, including UV rays, temperature fluctuations, and moisture. This durability ensures that GRP roofs often outlast many other roofing materials, making them a cost-effective choice in the long run.

2. Water Resistance: GRP roofs provide outstanding waterproofing properties. They create a seamless, impermeable membrane that effectively prevents water infiltration, minimizing the risk of leaks and water damage. This characteristic is particularly valuable for flat or low-slope roofs, where ponding water can be a common issue with other roofing materials.

3. Ease of Installation: While GRP roofing systems may require some skill and familiarity with the application process, they are moderately user-friendly, especially for individuals with experience in roofing installations. The availability of comprehensive GRP roofing kits, often accompanied by detailed instructions, can simplify the installation process and make it accessible to DIY enthusiasts and professionals alike.

4. Resistance to Environmental Factors: GRP roofing materials are highly resistant to various environmental factors that can compromise the integrity of other roofing systems. They do not deteriorate when exposed to sunlight, and they maintain their structural integrity in harsh weather conditions.

However, it's essential to acknowledge potential challenges associated with GRP roofing, such as its rigidity and the risk of problems arising from poor installation. Improper installation can lead to issues like ponding, flaking, cracking, alligatoring, guttering problems, pinholes, and surface holes or splits. Therefore, it is crucial to ensure that GRP roofing is installed correctly by qualified professionals to maximize its benefits and longevity. When properly applied, GRP roofing stands out as a reliable and long-lasting choice for flat roof applications.

What Are GRP Roofing Kits?

GRP (Glass Reinforced Plastic) roofing kits are comprehensive packages that contain all the necessary roofing supplies for the installation of a GRP roofing system. These kits typically include items such as liquid resin, catalyst, glass fiber mats, tools, safety equipment, and instructions to ensure a complete and successful roofing application.

Are GRP Roofing Kits Recommended?

GRP roofing kits are highly recommended for roofing professionals and experienced DIY enthusiasts who are well-versed in the installation process. They provide a convenient and efficient way to access all the essential materials and tools required for GRP roofing, ensuring that the installation is done correctly and efficiently. However, it's important to note that in most situations, for optimal results and to guarantee the longevity and performance of the roofing system, it is advisable to enlist the services of a qualified roofing professional. Their expertise and experience can ensure the proper application and reliability of the GRP roofing system.

What Are GRP Roofing Trims?

GRP roofing trims are specialised components used in GRP roofing systems to provide finishing touches and edge protection. These trims are typically made of the same GRP material as the roofing membrane and are designed to be used at roof edges, corners, and other vulnerable areas to provide a neat and watertight finish.

What Is The Benefit Of Using GRP Roofing Trims?

The benefit of using GRP roofing trims is that they enhance the aesthetics of the roofing system while also providing essential edge protection and waterproofing. They help create clean and professional-looking roof edges, ensuring that water cannot penetrate vulnerable areas.