How much does a fibreglass roof cost?
Published 3/26/2025
The average cost of a completed fibreglass roof in the UK is between £10,000 – 20,000.
If you are thinking of an extension, renovation or simply an upgrade to your existing home, you may be considering flat roof choices for your finished project.
In this guide, we will be looking at the factors that might impact the cost of your fibreglass roof and how much you might expect to pay using our helpful fibreglass roof calculator.
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Generally, fibreglass roof costs are calculated per m² in the UK and you will need to factor in labour costs as well as any materials needed.
Contents
- What is fibreglass?
- GRP fibreglass roof cost per m² calculator
- Why choose a fibreglass roof?
- What might impact the cost of my GRP roofing?
- How much does a fibreglass bay window roof cost?
- How much does a fibreglass conservatory roof cost?
- How can I reduce the cost of my fibreglass roof installation?
What is fibreglass?
Fibreglass is a widely used roofing material made from a mixture of fine glass fibres and strengthened plastic.
Also known as GRP (Glass Reinforced Plastic), it works well on buildings of all types due to its durable properties. It’s formed using a layer of polyester resin which is reinforced with glass fibres, creating a laminated layer.
Requiring minimal maintenance, it is one of the easiest roof materials to keep smart and clean.
GRP fibreglass roof cost per m² calculator
| Job description | Average cost per m² | Average job length |
| New roof with fibreglass finish | £180 – 230 | 3 – 5 days |
| Repair work on existing fibreglass | £50 – 90 | 1 – 2 days |
| GRP roof covering alone | £30 – 50 | 1 – 3 days |
| Fibreglass bay window roof | £90 – 120 | 1 – 2 days |
| Fibreglass conservatory roof | £30 – 40 | 1 day |
| Conservatory roof with additionally insulated panels | Additional £250 | 1 – 2 days |
| Get quotes | ||
Costs are based on averages and are variable depending on your location, specific job type and needs.
Why choose a fibreglass roof?
Value for money
Despite being recognised as one of the more expensive roofing choices, it offers arguably good long-term value for money.
It’s used reliably up and down the country in homes and commercial properties every day because it is strong and pleasing to the eye.
Protection from the elements
Fibreglass provides secure, long-lasting protection (typically up to 30 years).
Traditional felt roofing techniques are cheaper BUT offer only an average of 5 years before requiring maintenance or replacement.
Ease of installation
It is a common choice for roofers and consumers for both flat and inclined roofs as it can be applied directly as a covering to an existing roof deck.
Easy to work with due to its prefabricated nature and the fact that it requires no heat to install, it is also relatively straightforward to upkeep and complete simple maintenance on.
Long lifespan
When properly installed and well maintained, a fibreglass roof can be expected to last up to 30 years without replacement. It requires minimal maintenance and is very durable.
Protection from the elements
Fibreglass offers strong protection against water damage and is very water resistant by composition. It uses a seamless installation system so there is very little opportunity for water to penetrate.
It also provides the building with great UV, wind and snow protection, adding to longevity and structural integrity.
Insulation
Of course, a structurally sound roof alone will provide insulation to a building, but fibreglass roofs can be installed with added insulation.
This really bumps up that protection against heat escaping from your home and helps to make your property more energy efficient.
What might impact the cost of my GRP roofing?
You can expect a professional roofer to charge around £200 per m² on average for a fibreglass roof.
How much your GRP roof costs will depend on several factors.
Size of roof
The majority of roofers will work out the cost based on size.
Jobs are usually calculated on a cost per m² basis.
The larger the surface area, the more materials are needed and labour hours required, therefore the more you can expect to pay.
Type of job
Roof covering alone will cost around £35 per m².
GRP roof covering can be added to an existing roof to provide an extra layer of protection and longevity.
It is an ideal choice for installing over an existing roof surface. This will be a less expensive job than a full roof reconstruction.
The number of layers of fibreglass used will increase cost, as well as the differing material choices. Your roofer will be able to discuss options with you.
Location
As with any construction project, the cost of your fibreglass roof will be impacted by the area you live in. You can expect to pay more for your roof if you live in London or the south-east than you will for other regions of the country.
The complexity of your job
If your roof is an unusual shape or particularly hard to access then it may result in additional costs due to the increased length of the job resulting in added labour and material costs.
Existing roof quality
The average cost to install a deck can range from between £1,500 to 4,500 depending on size and materials chosen.
For a new roof to be constructed securely, the existing roof deck (the load-bearing foundation that the new fibreglass roof materials are added to) needs to be in a solid condition.
If this needs repairing or replacing as part of your job, it will cost significantly more than if your roofer can work with the existing roof deck.
Any additional factors such as asbestos removal will also incur costs.
Roof insulation
A fully insulated fibreglass roof will typically cost between £75 and £130 per m² and will take one to three days to install.
Installing or updating your roof insulation can save you up to £230 on your energy bills and 0.6 tonnes on carbon emissions.
A government grant may be available to support these costs.
Additional features
Higher-grade materials will be needed if the flat roof is going to be walked on regularly for safety. This would be particularly necessary for the additional footfall of balconies and roof gardens.
The thicker, more specialised coating will incur additional costs of around £8 – 15 per m².
Fibreglass guarantee
Longer guarantees will require additional layers of resin and will cost an additional £10- 15 per m².
Most roofers will offer a guarantee of varying lengths of time on your roof. The longer the guarantee you receive, the more protection from wear and tear you should receive, but this will also result in a higher cost.
Total insulated roof cost from joist to roof finish (without fascia, soffits, gutters) can be around £110 to £150 per m² for a 15 – 20 year guarantee. If you’d like to know how much fascias, soffits and guttering might cost for your project check out our cost guide.
How much does a fibreglass bay window roof cost?
You can expect to pay around £90 – 120 per m².
Fibreglass roofing is a common choice for bay windows. It can be moulded to any shape so provides a pleasing finish in relatively quick time.
How much does a fibreglass conservatory roof cost?
A fibreglass conservatory roof will cost around £30 – 40 per m², and up to £250 per m² for additionally insulated fibreglass panels.
A fibreglass conservatory roof offers increased energy efficiency, reduced maintenance costs and added value to the home if the job is done well.
Its lightweight material makes it perfect for this particular job. It helps to keep out pesky draughts and chills and keeps the space cool in those fleeting hot summer months.
How can I reduce the cost of my fibreglass roof installation?
- Make sure you use a trustworthy and experienced roofing company.
- Get a range of quotes and look at reviews before agreeing to anyone working on your project.
A badly installed fibreglass roof may result in rips, tears and degradation of the roof’s waterproof properties and lead to damp, leaks, mould and draughts.
It may seem like an expensive option, but fibreglass roofs are often more cost-effective when purchased with a guarantee as you are less likely to need to pay for future repairs or upgrades for a very long time, as much as 40 years potentially.
Post a job to talk to a local roofer and get a free quote today.
| Job description | Average cost per m² | Average job length |
| New roof with fibreglass finish | £180 – 230 | 3 – 5 days |
| Repair work on existing fibreglass | £50 – 90 | 1 – 2 days |
| GRP roof covering alone | £30 – 50 | 1 – 3 days |
| Fibreglass bay window roof | £90 – 120 | 1 – 2 days |
| Fibreglass conservatory roof | £30 – 40 | 1 day |
| Conservatory roof with additionally insulated panels | Additional £250 | 1 – 2 days |
| Get quotes | ||