Our Fibreglass Flat Roof Price Guide

Updated Fibreglass Roof Prices For 2021

Quotes From Dozens of Flat Roof Specialists

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Welcome to Quotation Check

How Much Does a Fibreglass Roof Cost?

Fibreglass is a tough, durable and long-lasting material that can be found on kayaks, ship hulls, surfboards, pond liners and hundreds of other waterproofed items.

It’s also one of three roof coverings that we recommend for flat roofs.

The other two are:

Rubber flat roof membranes; rubber is popular flat roof material and lasts for decades, explore our guide to rubber flat roof prices here.

Traditional bitumen roofing felts are still popular and often work our cheaper than rubber or fibreglass. See how much a bitumen flat roof costs here.

Keep reading to see how much a replacement fibreglass flat roof will cost you.

On this page we’ll cover:

  • An updated price guide for 2020/21.
  • How long the works take to complete.
  • A typical project schedule.
  • A loof at the materials needed to complete the project.
  • The best place online to compare prices from local installers.

We Asked 34 Flat Roofing Installers How Much They Charge

See how much we think a new fibreglass flat roof should cost

Here’s a Typical Project Schedule For a Fibreglass Flat Roof

This list describes the project:

  • Erect access equipment to the desired work height.
  • Remove the existing flat roof material.
  • Inspect the existing timber decking boards.
  • If the decking is sound, overlay new OSB decking, so there’s a new, clean surface for the fibreglass to adhere to.
  • If the timber decking is in poor condition, sagged or rotten etc. then it should be replaced with new OSB decking boards.
  • Install edging trims and upstands as required.
  • Install the fibreglass matt and coating layers to the decking.
  • Lower access equipment and remove all waste material.
Fibreglass roof kits

Photo shows all the items needed for a fibreglass installation except for decking boards, drip edges and upstands. Image source.

Our Fibreglass Flat Roof Price Guide

The prices below are an average of the figures given to us by roofing firms for several fibreglass flat roof projects:

Flat Roof Project 1 – Single Garage

We asked the 34 flat roofing firms for a price to replace a roof over a single garage.

The figures below are an average of the price given to us; they include the cost of new 18mm decking and also VAT when it was charged.

Not every project is the same so do check out our guide further down this page.

London Area£1600£1800
South, SW and Midlands£1500£1700
Outer Region and North£1200£1400
All prices inc standard decking. See notesAll prices inc standard decking. See notes.
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Fibreglass Flat Roof Price 2 – A Double Garage

The prices below are for a double garage, and as with the first price example, they include the cost of replacement 18mm OSB decking which is essential for the fibreglass to adhere to.

This is how much we think a flat roof project like this will cost, based on an average of the figures given to us.

London Area£2700£2900
South, SW and Midlands£2600£2800
Outer Region and North£2100£2300
All prices inc standard decking. See notesAll prices inc standard decking. See notes.
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Flat Roof Cost Guide 3 – A Small Porch

Fibreglass is often found on small porches and canopies.

The prices below are an average of the figures given to us, use this as a guide to fibreglass roof prices but do remember that every project is different and our guide further down the page lists some extra costs to consider.

London Area£800£950
South, SW and Midlands£750£950
Outer Region and North£600£750
All prices inc standard decking. See notesAll prices inc standard decking. See notes.
Need a Custom Price?Get a Quote

A Guide to Extra Costs

Timber Decking: Fibreglass can’t be laid onto old timber so new OSB 18mm decking boards should be installed first. This provides a suitable surface for the fibreglass to adhere to and a strong base that should prevent movement and cracks once the fibreglass has dried.

We’ve included the cost of OSB 18mm decking in our price guides:

OSB decking for rubber roofs

OSB Decking is extremely strong and durable and is perfect for fibreglass roofs.  Layers of wood slivers are held together with resin, creating a tough, water-resistant decking sheet.

Insulation and Insulated Decking: If your flat roof is above a heated part of the property, your installer will need to make sure there is enough insulation to meet the Building Regulations (Part L). That could mean paying for extra insulation or fitting an insulation-backed decking board (see image below).

We haven’t included the cost of flat roof insulation because most flat roofs are above porches, garages and sheds; none of these are heated so they don’t need insulation.

If you’re not sure if your current insulation will meet the Building Regulations, you can contact a flat roofing specialist to discuss your options or check out our quick guide to flat roof insulation.

Insulated decking

Insulated decking – perfect for roofs above heated parts of the property and meets Building Regulations Part L but costs more than standard decking.


Access Equipment: Our prices are for porches and garages, which are easy to access with basic access equipment. If your flat roof is difficult to reach, perhaps on top of a roof, or three-storeys high etc, then other more expensive access equipment such as scaffolding or access towers might be needed.

Optional Gravel/Stone Finish: Beauty is in the eye of the beholder and we like the smooth neat finish of fibreglass. However, some people choose to lay gravel over the fibreglass for aesthetic reasons. We haven’t included this in our cost guide and how much extra it costs will depend on how much gravel is needed.

VAT: The 34 roofing firms that gave us prices were both VAT registered and non-VAT registered businesses. We’ve included the cost of VAT in our guide when it was charged. You may find that businesses operating below the VAT registration threshold offer cheaper quotes than the prices we’ve suggested.

Extras: Most flat roofs will have guttering, fascias and sometimes soffits at the edges. We haven’t included a cost to replace these with Upvc plastic or to paint them. You may want to consider this extra work to finish off the flat roof neatly.

Compare Flat Roof Prices Online

We hope you found our guide to fibreglass roof prices insightful.

To get a custom price for your replacement flat roof project, tap the button below and fill in the contact form:

  • Get a custom flat roof price online.
  • Check vetted reviews and ratings.
  • Compare prices from local tradespeople and specialist firms.

Fibreglass Flat Roof Replacement

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Flat Roof Replacement FAQs

What is The Best Material For Covering a Flat Roof?

Rubber, also known as EPDM, has become popular over the last decade or so, and it’s easy to see why. This material lasts for decades, is easy to install as it doesn’t require the use of a naked flame. It often comes with long warranties and can be patch repaired should it get damaged in the future.

Fibreglass is a hard, tough material that lasts for decades but is prone to cracking if laid on weak, substandard decking that’s prone to movement. Hence why it’s vital the installer uses solid decking and not inferior, thin products.

Bitumen-based felts have been used on flat roofs for decades and are still one of the most popular products in use today. It’s also cheaper than rubber EPDM but doesn’t last as long and is more easily damaged by weathering and sunlight. Also, bitumen must be heated with a flame torch during the installation process, which introduces a fire risk.

When Were These Fibreglass Roof Prices Published?

We gathered these prices in 2020 and published this price guide in late 2020. We don’t expect the prices to change much over the next year or so except for inflation which is currently negligible.

How Long Will a Fibreglass Roof Last?

Most manufacturers offer warranties of between 10 and 15 years, but we’ve seen fibreglass roofs installed 25 years ago that are still watertight now. In our opinion, a fibreglass roof should last for 25+ years.

Of course, the life expectancy of the roof will depend on the workmanship and the condition of the timber decking underneath it.

One problem with fibreglass roofs is the potential for cracking. This usually only occurs on extensive roofs and when the decking and timbers underneath move as fibreglass is very rigid.

Do I Really Need New Decking?

Yes. Fibreglass should be laid over clean decking that’s strong enough to support the roof without too much flex. 18mm OSB decking boards are perfect for this type of roof.

There are only two occasions when we think you can leave the original decking boards in place:

  1. If they are in excellent, “as new” condition.
  2. They are in good condition, and new decking can be secured over the top of them.
My Existing Flat Roof is Pooling Water, Is This a problem?

Modern flat roof materials are designed to last years, even with water pooling on them.

However, in our opinion, your roof will last longer if most of the rainwater flows off of it rather than pooling on it. A few millimetres is fine, but any more than this could be a problem if you get a leak.

If your existing flat roof is holding water in a few areas that have sagged between the joists, then new decking should resolve the problem.

Some roofs are so badly built that rainwater flows in the wrong direction and pools, sometimes several centimetres high. The solution is for the installer to fit firrings under the new decking to raise one end of the roof.

If your existing flat roof is pooling water, contact a roofing specialist, make them aware of the issue and request a fibreglass flat roof price that includes the cost for new firrings.

How Long Does it Take to Install a Fibreglass Flat Roof?

It will take a team of two about a day to replace the decking and install the edgings and fibreglass finish to a single garage. A double garage will take between one and two days while a small porch will take ~half a day.  

Are There Any Associations Where I Can Find Vetted Roofers?

Several roofing associations in the UK hold databases of approved flat roofers.

The National Federation of Roofing Contractors and the Confederation of Roofing Contractors are good places to start.

You can also use our network of tradespeople, and of course, there’s also Checkatrade, Which?, Trustmark and other general associations.

Discover More Price Guides:

By Quotation Check

Bitumen Flat Roofs

An alternative to fibreglass is traditional bitumen-based torch-on felts. They don’t last as long but are often cheaper and have been used successfully for decades.

Rubber Roofs

Rubber roofing materials are extremely long-lasting, easy to install, and there’s no need for the installer to use a naked flame, so there’s no fire risk. They also look better than bitumen roofs, in our opinion.


Let us show you how much guttering and roofing projects cost in the UK. From repairs to maintenance to complete overhauls and replacements, check out our cost guides.

Their prices for roofline installations were correct; we were given quotes from several firms, all were similar to [Quotaton Check’s]

Quotation Check’s guides to flat roof prices are very accurate, they include all the extras many other price guides conveniently exclude.

Why only rely on three or four quotes for comparison? This website called Quotation Check gathered prices from hundreds of firms for various home improvement tasks and published their findings online.

Roofing firms often charge more than they should because they think consumers have no idea about how much the parts and labour should cost. Quotation Check’s guides are easy to read and they explain in detail about the materials needed and how long the work will take.

Go see the prices on the Quotation Checker website; they’re suggesting a price for a new roof that’s much lower than that.