Flat Roof Prices and Costs

Welcome to Roofer’s Rates – A website created by roofing contractors for homeowners. Find out how much you should expect to pay for roof repair work. What are the typical flat roof costs you can be expected to pay for repairs/replacement to your flat roof covering?

This page was last updated on the .

Don’t forget; this is just one several cost guides. See our full price list here.

Our Flat Roof Guide

Our price guide below is for a flat roof located in the south of the UK but outside of London. Our research shows that you should add 10-20% to the price if you live in London. If you are located in the north or far south west, you may find that this type of work is slightly cheaper than the figures we have displayed below.

Flat roof felt costs

Mineral felt being torched to mid-layer

Replacement Flat Roof Felt to Single and Double Garage

The price below is the cost you can expect to pay for replacing the roof covering on a single garage with a two layered torch-on system:

Single Garage Flat Roof Cost - £550+Vat

Below is our guide price for a typical felted double garage, this is again for a two layer system:

Double Garage Flat Roof Cost - £900+Vat

To upgrade to a three layer flat roof system, add £150+vat to the cost of a single garage and £250+vat to the cost of a double garage.

You do not need to lay stones on the flat roof to protect the felt from UV light as the felt already has a mineral finish that protects it. Stone chippings are optional and for the most part they’re decorative. Expect to pay around £80-100 for your roofing contractor to purchase and lay stone chippings on top of the flat roof felt.

Roof Decking

The timber decking located underneath the felt is designed to keep the felt flat and prevent water ponding. If the decking is wet, rotten or in a poor state it will need to be replaced. There is little point in laying felt to a flat roof that is unsound.

Cost to Replace Decking - £40-50+VAT (per sheet)

A typical single garage has between 5-6 decking boards.

You may only need to replace a small number of boards. Perhaps if your roof had a leak in one area but the remaining boards are in good condition.

EPDM Flat Roof Price

These roof coverings are an alternative to traditional torch-on roof felt. They have been in use for over a decade and are now as popular as traditional torch-on felts. Often called “rubber roofs” the material can be laid without the use of a gas torch so there is no naked flame, hence why they are popular on public buildings where health and safety requirements are more stringent.

Epdm is more expensive than torched flat roof felt and it’s important that the decking underneath is in excellent condition.

The guide price below is for a single garage flat roof:

Cost to Install Rubber Roof Covering - £900+VAT

Fibreglass Flat Roof Costs

Fibreglass is tough and durable and lasts for many years. It is made from a resin that contains small amounts of glass fibres. Fibreglass doesn’t bend or flex so much so it’s important the decking underneath is sound.

The figures below include overboarding. This is where the existing boards are left in place but new OSB boards are fitted above them. The fibreglass is then installed to the new boards.

The guide price below is for fibreglass to a single garage flat roof, including new decking overboards:

Fibreglass to Single Garage - £1450+VAT

Expect to Pay More if…

If your flat roof is located 3 storeys up or located in a rear garden with serious access issues then it will cost more to have the work done.

If you want insulation, ventilation or if the roof is unusual in anyway then expect to pay more.

Location – as stated earlier location will affect the cost of a flat roof replacement. London is the most expensive area but the south east is also a pricey area.

You Can Save Money if…

If your flat roof area is very large or you you are having more than one flat roof replaced at the same time.

Can you dispose of the waste material yourself? Perhaps you have a skip on site for another project and there is enough space for the old felt? Commercial waste disposal yards charge upwards of £80+vat per tonne, many have a minimum charge of around £100.

Waste Disposal

The removal and disposal of the waste material is included in the figures above. Your contractor should take all the rubbish to a waste recycling and disposal yard.

It’s unlikely that a skip would be used as that would add considerable cost, is unlikely to be fully filled and would most likely block the driveway that the roofers need to park their van on to unload the decking sheets, felt and other materials.

Pro Tip:

This part of our page is where we share some top tips and advice that can either save you a packet or ensure your new flat roof lasts as long as possible.

  1. We suggest you avoid having torch-on bitumen based felts laid down in temperatures exceeding 30degrees – it will likely shrink during the cold winter months and may compromise the seal.
  2. While it’s cheaper to leave any old felt in place and lay the new materials on top of them,  this approach will shorten the life expectancy of the new felt. Most manufacturers offer ten or even twelve year guarantees on their products, but only of the substructure is sound, having old rotten felt underneath your new felt covering is therefore not recommended.
  3. If your existing flat roof is holding water, ask your chosen roofing company for a price to ensure that the new roof is constructed in such a way that all the rainwater flows freely to the guttering. This might be as simple as changing a few decking boards that have bowed/sagged or it could involve some extra work. If it’s not too expensive then it’s worth doing as excessive amounts of water ponding on the roof can reduce its life expectancy.
  4. If your flat roof is shared with a neighbour, perhaps a shared double garage then try to get both roofs done at the same time, it should work cheaper for you both and there won’t be an unsightly join halfway across the roof.
  5. For garages and other storage areas use a two-layer torch-on felt system, for roofs over habitable parts of the property use a 3 layer torch-on felt system. Rubber roof coverings and fibreglass are the same thickness regardless of where on the house they are located.

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