Fibreglass roof vs Felt roof – which is best?

Neil Boylan

Contracts Director

Posted on November 6, 2023May 3, 2024

When looking to specify a weatherproofing system on your commercial flat roof project to protect it from the elements, there are several different membrane types available. Here we look at two popular choices – a more traditional felt based system, or a more durable fibreglass roof solution. It is worth noting that a fibreglass roof is more commonly known as a glass-reinforced plastic (GRP) roof and for the purposes of this blog we will refer to this type of roof this way.

Each of these has their own benefits and ultimately the system selected will be determined by the specific needs of the project. Installing a glass-reinforced plastic roof, however, generally offers more design freedom, is safer to install, with no requirements for hot works, and is more durable, offering increased longevity. Fibreglass also has increased resistance to fire spread which is an important consideration in any flat roof specification.

Felt covered commercial flat roofs

A traditional felt covered commercial roof uses a bituminous felt membrane which is hot applied using a flame – more commonly referred to as a torch-on application. The weatherproofing membrane is usually made up of three layers of material – one or two layers of bitumen felt – and a finishing layer of mineral felt.

A gas torch is passed over the underside of the bitumen layer, causing it to become an adhesive. A roller is then used to apply pressure to the layer so that it bonds to the roof surface. The felt is applied in sections leaving a seam where the sections meet. The seam is the weak point of the roof’s weatherproofing layer and tends to be where failure may occur first.

For many project types, particularly domestic and smaller commercial roofs, a traditional felt weatherproofing membrane is a popular choice and offers several benefits including:

Cost – Compared to a GRP roof, a felt weatherproofing membrane is usually cheaper, although in the long term, the increased lifespan of fibreglass can more than make up for this.
Lifespan – A properly installed felt roof covering can typically be expected to last for eight to ten years.
Ease of transport – Felt used for roofing is supplied as a roll which is compact and reasonably lightweight, allowing easy transport to site.
Flexibility – Roofing felt is a very flexible material and can be easily moulded and shaped to fit the roof structure it is being applied to.

GRP fibreglass architectural mouldings commercial clients

Glass-reinforced plastic (GRP) covered commercial flat roofs

Glass-reinforced plastic makes a great choice for use as a weatherproofing layer. The membrane is applied to the roof using a resin adhesive and bonded to the roof surface giving it a strong, protective layer with no seams which tends to be the first point of failure in more traditional weatherproofing membranes, including felt.

To install a GRP weatherproofing membrane, a layer of resin that has been mixed with a catalyst is applied to the roof deck, a sheet of fibreglass mat is then laid onto the resin followed by a finishing layer of resin. This forms a tight, weatherproof seal with high UV light resistance. A glass-reinforced plastic roof also has excellent resistance to fire, making it a safer alternative to traditional felt based systems. Pigment can be added to the final coat of resin meaning the roof can be finished in a colour to match any design requirements.

When considering GRP as the weatherproofing membrane for your roofing project, it can be useful to learn the benefits that this system can provide.

Safer to install – A glass-reinforced plastic roof is cold applied; therefore, no flame (hot works) is required for installation.
Longevity – Research shows that a properly maintained roof of this type can last for 30 years or more.
Maintenance – GRP roofs are easily maintained. Occasionally, leaves and debris should be removed, and the surface given a wash with a mop.
Visual appeal – The top layer of a GRP roof can be coloured to match any aesthetic requirements.
Durability – This type of roof has no seams which tend to be the weak points of a traditional felt based covering.
Fire resistance – Fire safety is of paramount importance in all construction and GRP benefits from increased resistance to fire spread.
Strength – A glass-reinforced plastic roof offers excellent resistance to the effects of foot traffic and impact from debris including tree branches, hail and dislodged masonry. Additionally, this type of roof is more tolerant to the effects of UV light.
Seamless finish – The surface of a GRP roof is a continuous layer with no seams or joints, this makes the roof much less susceptible to damage from water ingress and gives a more visually pleasing finish.

Is GRP the most suited weatherproof layer for commercial flat roofs?

Commercial building flat roofs tend to be large areas which, if finished using a traditional felt weatherproof membrane, will have multiple seams or joints where the layers meet, increasing the potential for water ingress and failure. GRP roofs are applied with no seams making them a much more durable solution.

Glass-reinforced plastic can be easily moulded to form complex shapes and the final layer of resin can have pigment added to create a coloured finish.

A traditional felt roof contains bitumen which is flammable whereas GRP has an increased resistance to fire making it a much safer product for use in roof weatherproofing. The installation process for a felt roof requires the use of a flame torch, some projects – notably schools and hospitals – may have restrictions on the use of torch-on systems and a cold-applied finish such as glass-reinforced plastic is usually the preferred solution.

Jones and Woolman are a UK company based in the West Midlands, since 1979, they have been providing roof penetrations, weathering and GRP Mouldings solutions. As approved expert installers of cold-applied liquid GRP roofs, Jones and Woolman UK can provide a complete roofing service from initial site surveys through to the design and installation of the roofing system.

To discuss using a GRP roof on your next project or any of our other solutions please get in touch here.

What are the benefits of fibreglass roofs?

by Neil Boylan

Neil Boylan

Contracts Director

Posted on May 26, 2023May 3, 2024

Fibreglass roofs (also referred to as GRP roofs) are a popular choice for commercial buildings. On a traditional flat roof build-up, a fibreglass weatherproof layer offers numerous benefits over alternative solutions, such as single ply and bitumen-based layers, to name a few. These benefits include:

Increased durability
Lower maintenance requirements
Easier to repair
A stronger weatherproofed seal
Increased energy efficiency
Broader aesthetic design

Fibreglass (GRP) is made from thin strands of glass woven into a mat. The fibres are combined with a resin and form a strong, flexible product which can be easily moulded into a variety of shapes. This makes Fibreglass (GRP) an excellent choice where complex detailing is required. Pigment can also be added to the resin to create a wide range of colours.

Compared to a traditional bitumen-based and single ply weatherproofing layer, fibreglass offers higher resistance to foot traffic and impact from objects including, but not limited to, hail, dislodged tiles from neighbouring buildings or tree branches. The ease of maintenance and life expectancy of over 30 years, with correct installation and maintenance, makes fibreglass flat roofs a very attractive specification option for commercial buildings.

What is the durability of a fibreglass roof?

Fibreglass is a durable and long-lasting material that can withstand harsh weather conditions such as extreme temperatures (both hot and cold), wind, rain and hail strikes. In addition, fibreglass has high resistance to the effects of UV light. A fibreglass flat roof is installed with no seams, creating a continuous surface which is highly resistant to water ingress. A properly installed fibreglass roof will have a long lifespan and require minimal maintenance.

Research shows that a properly maintained fibreglass roof can last for 30 years or more compared to around 20 years for a traditional bitumen felt based roof covering.

How much maintenance does a fibreglass roof need?

As with all roofing systems, to ensure that they perform as intended for the life of the building and look their best throughout the years, they should be regularly inspected. Reputable flat roof weatherproofing installers may offer warranties that cover their products and installation. These warranties can be very beneficial and long-term (up to 25 years in some cases), however, regular inspections, with around one a year, may be required to maintain this benefit.

Because of the durability and longevity of GRP fibreglass, however, the only expected maintenance typically required for fibreglass flat roofs is to keep them clean – this helps the surface maintain its striking finish. Cleaning fibreglass flat roofs simply involves removing debris, such as leaves, tree branches, moss, or other growth and giving the surface an occasional wash with a mop.

GRP fibreglass for curves installed on a building

Fibre Glass Flat Roof with a railed off window on the right-hand side

Are fibreglass roofs difficult to install?

Fibreglass is a lightweight material that is cold applied meaning no torch or flame is required to heat the membrane. This can reduce the installation time and avoids the need to use bottled gas and torches (hot works). The fibreglass layer is applied using a roller and a resin topcoat provides the tough, final finish. An easier installation saves considerably on time and costs.

Is a fibreglass roof more expensive than a traditional system?

The belief that fibreglass is a more expensive system is a misconception when looking at the overall long-term picture. The lifespan of a fibreglass membrane itself is typically longer than that of felt or single ply solutions. The higher initial cost of a fibreglass finish is offset by the longer lifespan of the roof. This means that overall, there is a long-term cost benefit to using fibreglass.

Fibreglass roofs and fire performance

Fibreglass has high resistance to the spread of fire which is an important consideration when specifying a roof. A roof must satisfy the requirements of the Building Regulations Approved Document Part B which applies to fire safety in construction. Section B4 covers the requirement of the external walls and roof of a building to adequately resist the spread of fire over the walls and roof of the construction, as well as from one building to another. The full document can be freely downloaded here for more information.

We provide a complete roofing service from initial site surveys, as well as design and installation of a roofing system, through to aftercare and are approved installers of cold-applied liquid fibreglass roofs.

To find out more, please visit the fibreglass roofs solutions page and contact us for any project requirements around fibreglass roofs.

How much maintenance do fibreglass roofs require?

by Matthew Jones

Matthew Jones

Commercial Director

Posted on May 26, 2023May 26, 2023

As with all roofing systems, fibreglass roofs should be regularly inspected to ensure that they perform as intended for the life of the building and look their best throughout the years. Reputable flat roof weatherproofing installers may offer warranties that cover their products and installation. As these warranties can be beneficial, and in some cases long-term (up to 25 years).

Because of the durability and longevity of GRP fibreglass the only expected maintenance typically required for fibreglass flat roofs is to keep them clean – this helps the surface maintain its striking finish. Cleaning fibreglass flat roofs simply involves removing debris, such as leaves, tree branches, moss, or other growth, and giving the surface an occasional wash with a mop and soapy warm water.

How often should a fibreglass roof be checked?

It’s a good idea to carry out a visual check on a fibreglass roof at least once a year and after any severe weather, particularly hail and high winds. This check can be carried out by the building owner/inspector or a professional roof covering installer for greater peace of mind. Any damage that has occurred can therefore be addressed before it becomes a bigger problem. If there are trees located close to the building, these can cause issues with cleanliness and should be trimmed regularly. Additionally, any blocked drains and gutters should also be regularly checked and cleaned out.

Fibre-Glass-Flat-Roofs with obstructions

How frequently should a fibreglass roof be cleaned?

Cleaning a fibreglass roof should be carried out at least once a year and can be part of a standard maintenance regime, without the need for specialist help. However, depending on the roof structure, building height and access requirements, maintenance may require an expert. This is particularly true for commercial and industrial applications. Drainage points and gutters should be cleared of any material such as leaves and debris to ensure water is able to freely flow from the surface and avoid build-up.

Fibreglass roof maintenance and safety

When working at height, such as on a roof, it’s important to ensure safe practice, and working at height precautions must be taken. Guidance regarding working safely on roofs is provided in the Health & Safety Executive document HSG33 which can be found here.

Jones and Woolman UK, established in 1979 and based in the West Midlands, provides roof and vertical penetrations, access hatches, upstands, weatherproofing and GRP moulding solutions. Jones and Woolman UK provide a complete roofing service from initial site surveys, as well as design and installation of a roofing system, through to aftercare and are approved installers of cold-applied liquid fibreglass roofs.

To find out more, please visit the fibreglass roofs solutions page and contact us for any project requirements around fibreglass roofs.

GRP flat roof repairs and installations

by Matthew Jones

Matthew Jones

Commercial Director

Posted on June 12, 2019May 26, 2023

The traditional method for finishing a flat roof is with a combination of felt and bitumen. Although this option does provide an attractive and durable result, it’s not particularly reliable over the long term. That’s why GRP roof repairs and roof installations are becoming increasingly popular.

GRP (also known as glass-reinforced plastic or fibreglass) is an extremely strong yet lightweight material that can be quickly and easily applied to flat roofs, providing a robust and weathertight finish that should last for many years. It is suitable for a wide range of projects, from domestic applications like small garden sheds, garages and house extensions, all the way through to massive commercial buildings like sports stadia and shopping centres.

The benefits of GRP roofing

GRP offers a number of benefits over traditional felt roofs – from its lifespan to its resistance to weather impact, mould, rot and fire. It is cold-applied, simplifying the installation process, and it can even be applied over existing roofing solutions, so you don’t need to worry about removing the old roofing materials before carrying out flat roof repairs.

Flat roofing: GRP vs felt
	GRP	Felt
Expected lifespan	25+ years	5-10 years
Can be installed over an existing solution	✓	X
Resistant to fire	✓	X
Capable of withstanding regular foot traffic	✓	X
Mould and rot resistant	✓	X
Weather resistant	✓	X
Cold applied	✓	X
Quick installation	✓	X

When a flat roof needs to be repaired, a quick solution is essential. After all, water and wind can cause a lot of damage in very little time. One of the main benefits of GRP – both for flat roof installations and repairs – is that it’s a cold-applied liquid, meaning that it is quick and easy to install. This is also advantageous for new roof projects, as it means you won’t have to wait long for the roof to be completed.

GRP is also a versatile material, and that’s why we also use it to construct other elements of a roof – such as architectural mouldings and upstands for roof windows and ventilation units, and it can be used to provide reliable weatherproofing around building penetrations.

GRP roof repairs and flat roof installations from Jones and Woolman UK

Here at Jones and Woolman UK, our team has extensive experience in both installing GRP flat roofs and carrying out flat roof repairs.

We work with a wide range of customers, from homeowners wishing to carry out improvements or repairs, through specifiers responsible for large commercial buildings. No job is too big or too small, and we are committed to providing a high level of service to every one of our customers.

Every month we buy in around two metric tonnes of GRP, and buying in bulk like this saves us around 40% on materials – savings that we pass on to you.

Whether you’re looking to repair a flat roof or install a new one, and whether it’s a garden shed or an international airport terminal, Jones and Woolman UK can help. To find out more or to discuss your project in more detail, please don’t hesitate to get in touch.

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