Our Guide to Flat Roof Repairs and Replacement

Updated For 2021

Cost to Repair or Replace Flat Roofs

A Look at Environmentally-Friendly Options

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Part of Our Roofing Series

Flat Roof Options

Flat roofs can be constructed from a variety of materials, but most of will them have timber decking underneath a covering of either fibreglass, rubber, bitumen felt or something similar.

In general, flat roofs require more frequent attention than pitched roofs made from concrete or slate tiles. A flat roof that’s installed to a high standard and using modern materials should still last well over 25 years with some materials such as rubber keeping water out for over 30 years.

On this page, you’ll find links to:

  • Price guides for replacement fibreglass, rubber and bitumen flat roofs.
  • Decking; how, when and why it sometimes needs to be replaced. Also, a look at decking prices.
  • Insulation, when you need to install it to meet the Building Regulations and how much it costs.
  • How to create a “green” environmentally-friendly roof + a look at prices.
  • A look at flat roof repairs, their cost and feasibility.

1) Fibreglass Flat Roof Price

Fibreglass is a tough, durable material that’s constructed in layers to create a waterproof barrier.

Often found on ship hulls, kayaks, pond liners and thousands of other items, it’s also perfect as a flat roof covering.

Fibreglass isn’t the cheapest option, you’ll need to install new costly timber decking for the materials to adhere to, but it does last for decades.

Tap the button below to see our price guide for fibreglass flat roofs; you can also get a custom quote from one of our partners.

Fibreglass Roof

2) Rubber Flat Roof Cost Guide

Rubber is a modern flat roof material that has proven itself to be waterproof, easy to install and repairable over the last 20 years.

We recommend installing rubber roof membranes over new decking, so that does at to the cost of the project.

One advantage of rubber over bitumen is that a naked flame isn’t needed during the installation, so there’s no fire risk whatsoever.

Tap the button below to see our updated rubber flat roof price guide:

Roll of rubber membrane

3) Bitumen Flat Roof Guide

Bitumen felts have been used successfully for decades on flat roofs, they are one of the cheaper options and can be installed over existing decking boards, provided they are in good condition with no signs of rot or sag.

The rolls of felt are lined with a tar-like substance called bitumen which is heated with a naked flame to weld the layers together.

Bitumen felt flat roofs don’t last quite as long as rubber or fibreglass and are prone to weathering, especially from sunlight. However, with proper installation, you should still expect a lifespan of between 15 and 20 years.

Tap the button below to see how much a bitumen flat roof costs.

Flat roof bitumen felt system

4) Flat Roof Decking

Decking is the material sandwiched between the roof joists and the felt or covering. It provides support and helps to keep the flat roof rigid.

Without adequate timber decking, the roof covering may sag, crack, split and fail, which can lead to leaks.

When a flat roof is renewed, the decking may or may not need to be replaced, it all depends on the condition of the decking and the type of flat roof covering you want to be installed.

For example, fibreglass should be laid onto new, clean decking boards and never onto older boards.

You have several options and our guide, which includes prices, can help you:

OSB decking for rubber roofs

5) Insulation: The Regulations and Your Options

The Building Regulations were updated in 2010 and since then, some flat roof refurbishment projects can only be completed if adequate insulation is present.

There are several options, some that cost more than others and to muddy the waters, some flat roof projects won’t need any insulation at all.

Our guide makes sense of the regulations, suggests prices for insulation and provides links to official resources.

Tap the button below to find out more about flat roof insulation.

Insulated decking

6) Green Environmentally Friendly Flat Roofs

Bitumen felts have been used successfully for decades on flat roofs, they are one of the cheaper options and can be installed over existing decking boards, provided they are in good condition with no signs of rot or sag.

The rolls of felt are lined with a tar-like substance called bitumen which is heated with a naked flame to weld the layers together.

Bitumen felt flat roofs don’t last quite as long as rubber or fibreglass and are prone to weathering, especially from sunlight. However, with proper installation, you should still expect a lifespan of between 15 and 20 years.

Tap the button below to see how much a bitumen flat roof costs.

Green roofs

7) Flat Roof Repairs: A Look at Prices and Feasibility

Bitumen felts have been used successfully for decades on flat roofs, they are one of the cheaper options and can be installed over existing decking boards, provided they are in good condition with no signs of rot or sag.

The rolls of felt are lined with a tar-like substance called bitumen which is heated with a naked flame to weld the layers together.

Bitumen felt flat roofs don’t last quite as long as rubber or fibreglass and are prone to weathering, especially from sunlight. However, with proper installation, you should still expect a lifespan of between 15 and 20 years.

Tap the button below to see how much a bitumen flat roof costs.

Flat roof repairs

Compare Flat Roof Prices Online

We hope you found our guides to repairs, replacements, prices and other information useful.

If you want independent advice or a quote for any flat roofing project, just tap the button below.

  • Post details of your project to the job board for free.
  • Interested specialist will contact you.
  • Compare prices and advice from several local firms and specialists.

Flat Roof 

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Flat Roof FAQs

What is The Best Flat Roof Covering?

Each material has its own pros and cons but here are the three options:

EPDM, also known as rubber, has become increasingly popular over the last decade or so. The material has longevity as it lasts for decades and is easy repair should it become damaged. Most installers and manufacturers offer longer guarantee periods too.

Fibreglass is a material that’s been used on ship hulls, kayaks, pond liners and other products for years. It’s tough, durable and can be patch repaired easily. It should be installed over new decking otherwise it may not adhere correctly.

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 Flat Roof Prices Published?

We published prices for fibreglass, bitumen and rubber flat roofs in early 2021.

Which Type of Covering Lasts the Longest?

Rubber lasts the longest and is resistant to sunlight and weathering, it’s also very flexible so won’t crack if the roof underneath suffers any movement.

Fibreglass is also a long-lasting material but due to its rigidity, may suffer from cracks if the roof underneath experiences movement.

Bitumen felts are the cheapest option and last the least amount of time, but you can still expect a lifespan of around 15-25 years if installed correctly. They are affected by sunlight and general weathering but extra layers can increase the life expectancy.

 

Do I Really Need New Decking With My New Flat Roof?

Fibreglass and most rubber membranes should be installed over new timber decking boards while bitumen felts can be laid over old decking provided it hasn’t sagged or is rotten.

In some cases, new decking boards can be installed over the old boards instead of replacing them, thus reducing the cost somewhat.

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 roof 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 Flat Roof?
It will take a team of two no more than a day to replace the decking and install the covering of a typical single garage roof. A double garage will take between one and two days while a small porch will take around half a day. If you want a green roof installed, new guttering, new roofline boards or any other extras such as insulation, the project will take longer.
Are There Any Associations Where I Can Find Vetted Roofers?

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

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 Roof 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.

Fibreglass Roofs

While fibreglass is the toughest flat material, it’s also one of the most expensive to install. See our guide to fibreglass flat roof replacement prices for more information.

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.