If you are a looking to replace your roof and you are aiming for a flat roof, you are certainly worried about how much it is going to cost you. Fortunately, we share your concerns and this is why we have created this detailed cost guide.
Flat roofs date back to 2000 BC, during the Minoan period. They were constructed of timber or thatching to block out bad weather in those days, but now things are a little more advanced than that! Before you decide on installing a flat roof, it is worth considering the cost vs. maintenance factor – whilst flat roofs generally cost less to install, they often cost more in maintenance costs over the years.
On this page
- How to use this guide
- What are the benefits of a flat roof?
- What are the disadvantages of a flat roof?
- What types of flat roofs are there?
- How much does a flat roof cost?
- Flat roof cost
- Flat roof cost per square meter
- Flat Roof Prices – Examples
- Flat roof insulation
- GRP flat roofing
- Flat roof repairs & maintenance
- Roof Inspection Checklist Before Repairs
- Flat roof inspection advice
- Roof Inspection Checklist
How to use this guide
Even though this article is well researched and tries to provide as much as possible accurate estimations, flat roof prices will always vary depending on the local roofer’s rates. Please try to read this article carefully and use it mostly as a guide.
What are the benefits of a flat roof?
Cost: Constructing a flat roof usually takes less time and uses fewer materials than a traditional roof, which means it costs less to install.
Warmth: Flat roofs can keep your home considerably warmer than their competitors, especially during the cold winter months. This is because the flat surface area attracts sunshine which then penetrates the home below.
Versatility: Versatile internal and external space. It can be used as a patio, garden, outdoor swimming pool, or a communal outside area.
Accessibility: Flat roofs are more accessible, making it easier for new installations and repairs.
What are the disadvantages of a flat roof?
Draining: The biggest disadvantage of installing a flat roof is the danger of water and other debris gatherings, which gradually can make the roofing material break down or crack.
Maintenance: This is a significant factor when considering installing a flat roof, as they require many.
Lifespan: The average lifespan of a flat roof is 20 years, and that’s only if it is properly maintained.
Materials: There is a lack of roofing materials available to use, and the vast majority of flat roofs use rubber, EPDM, TPO, or bitumen, which are relatively cheap and easy to install but have a short lifespan of 10 -15 years.
Styling: This is another limitation, mostly because of the lack of materials. However, who can now use rubber singles in conjunction with rolled-up roofing and several other materials such as polycarbonate roofing and PVC roofing that can improve the styling of the roof at a higher cost.
What types of flat roofs are there?
Any material used to construct a flat roof must be watertight because even though flat roofs are built on a slight incline, they are still very susceptible to leaks. That said, there are five main types of flat roofs: roll asphalt, single-ply, multiple-ply, modified ply, modified bitumen, and flat-seamed metal.
- Roll asphalt flat roof
Roll asphalt comprises layers of asphalt-coated fiberglass, tar, felt, and water-resistant materials, all of which are kept in place with nails or asphalt cement. The top layer is covered with gravel, which protects the roof from ultraviolet rays. This type of flat roof has been used for over 100 years and is generally the cheapest; however, it doesn’t usually last much longer than 10 years.
- Single-ply flat roof
Single-ply flat roofs are made from one layer of materials that are a bit like rubber. These materials cost less but are studied and more energy-efficient than roll asphalt roofs. Usually, single-ply roofs are made from EPDM, uPVC, ethylene, and TPO. These are all mold-resistant and low-maintenance. Single-ply roofs usually last for up to 12 years.
- Multi-ply flat roof
This type of flat roof comprises lots of layers of fiberglass, which is packed between layers of asphalt. The big benefit of multi-ply flat roofs is that they are reinforced, lasting longer, and are less damaged. They can last as long as 30 years.
- Modified Bitumen flat roof
Some multi-ply flat roofs use a modified bitumen membrane, which is made from a mixture of polymers and asphalt, making it flexible and water-resistant. The top layer is covered with gravel. These types of flat roofs could last up to 20 years.
- Flat-seamed metal flat roof
This is the most expensive type of flat roof, largely because it is made of metal such as copper and stainless steel. Metal flat roofs usually last between 20 and 50 years.
How much does a flat roof cost?
The price of flat roof replacement in the UK depends on factors like:
Flat roof specifications: Each job is different and presents different difficulties.
How accessible is the roof: The height of the roof and whether scaffolding is required or not.
The location: If the cost of living is significantly higher, you should expect the charges to be higher.
Tradesman Mark-Up: Each business needs to make a profit. Also, if a tradesperson has an excellent reputation and is very busy, the prices are usually higher as they can choose the jobs to a certain extent.
The size of the project: For small projects, the cost is usually higher per square meter due to time-saving and workforce considerations.
Flat roof cost
According to our research, the cost of building a flat roof in the UK ranges from £1,700 to £4,500, depending on the number of rooms and the type of property you own. Flat roof extensions cost £700 (lowest possible) and can reach up to £3,000. For bay windows, roofs expect to pay from £350 – £900 and for dormer window roofs between £700 – £1,300. More details can be seen in the table below:
Cost of a new flat roof
|1 Bed House||2 Bed House||3 Bed House||4 Bed House|
|Main Roof (Cost of a flat roof)|
|£1,700 – £3,000||£2,000 – £4,000||£2,500 – £4,500||£3,300 – £4,500|
|£700 – £1,700||£1,000 – £2,500||£1,300 – £2,700||£1,500 – £3,000|
|£350 – £650||£400 – £700||£450 – £750||£500 – £900|
|£700 – £1,100||£750 – £1,200||£800 – £1,200||£800 – £1,300|
|£300 – £500||£400 – £600||£450 – £600||£500 – £600|
Flat roof cost per square meter
Flat roof prices start from £40 per m2 for felt roofs. Rubber roofs costs start from £80 per m2. For fiberglass, expect to pay from £90 per m2 and for fire glass bay roof from £250 per square meter. Lead bay roofs are even more expensive, starting from £300 per m2.
|Flat Roof Prices Per Square Metre
|Job Type||Cost Per Square Meter||Specifications|
|Felt Roof||£40 – £50 + £40 if the boards are damaged||This is a modern felt roof or built-up felt roof. It is also known as a Torch-on flat roof.|
|Rubber Roof||£80 + additional cost if the boards are damaged||A Modern Flat Roof similar to Firestone that is also known as E.P.D.M.|
|Fire Glass||£90 (trims and lead flashing included)||A modern fiberglass GRP flat roof system with specialized roofing grade resins. Price does not include over-boarding with OSB, which is necessary to adhere to a new fiberglass roof.|
|Fire Glass Bay Roof||£250 – £490 + 50 (stripping and insulating)||Even though the size is tiny, the cost increases due to trim and time spent fitting. For approximately an additional £50, the window can also be stripped and insulated|
|Lead Bay Roof||£300 + lead costs||Prices can vary significantly due to different project specifications and the many different options of lead code, and the cost of raw material.|
Flat Roof Prices – Examples
Flat roof insulation
Heat rises and will escape quickly through an un-insulated roof. Installing insulation on your flat roof will help to prevent this from happening, keeping your home warm and saving you money on your fuel bills. Flat roofs are made up of several layers: the roof deck, a vapor control layer, a thermal layer, a waterproofing layer, and a surface layer.
The layers that make up a flat roof
The roof deck can be made of metal, timber, concrete, composite, or plywood and will support your flat roof. “According to cutmyplastic.co.uk, the plywood roof deck provides significant protection and is the most affordable.” The vapor control layer can be polymeric foil, a bitumen sheet, polyethylene membrane, or a self-adhesive sheet. The thermal layer of the flat roof is used for insulation and is made of materials that trap air bubbles and air pockets to insulate the flat roof. Common materials used for insulation are mineral wool, fiberglass, or polystyrene.
The waterproofing layer of the flat roof is commonly made up of single-ply membranes such as thermoplastic or elastomeric; uPVC or resin surfaces are also an option. A surface layer of stone chippings, hard resin, or mineral finish is often applied to protect the waterproofing layer. It can be difficult to know which is right for your roof, but your roofing contractor will advise you on what is needed.
Wood fiber roof insulation
Wood fiber insulation is an organic board made of wood, cane, or vegetable fibers mixed with various binders and fillers. It can be asphalt impregnated or coated to improve its water resistance. It has a thermal resistance value per inch of 2.78, making it fairly mediocre as insulation for a flat roof but good value for money.
Perlite roof insulation
Perlite insulation is composed of perlite combined with organic fibers and binders. Air cells are trapped within the perlite, which provides the insulation for your flat roof. The insulation board is treated with an asphalt coating to limit asphalt absorption into the insulation. Like wood fiber, it has a thermal resistance value of 2.78.
Expanded and extruded polystyrene roof insulation
Polystyrene insulation for your flat roof comes in two forms – expanded and extruded. Expanded polystyrene is made up of polystyrene mixed with a foaming agent. When exposed to heat, the material expands and traps warmth. It has a thermal resistance value of 3.80. Extruded polystyrene is made of polystyrene that is heated, exposed to atmospheric conditions, and then expanded. Its thermal resistance value is 5, making it a good choice for your flat roof insulation.
Polyisocyanurate roof insulation
Polyisocyanurate insulation is sandwiched between organic and non-organic felt within your flat roof. A blowing agent such as pentane is used to expand the foam material, which gives it its high thermal resistance of 6.0.
Cellular glass roof insulation
Cellular glass insulation for your flat roof is composed of crushed glass placed in a mold and heated to a high temperature. It is available in flat or tapered blocks and provides a thermal resistance of 4.69.
Living, green roofs
“Cool” flat roof: Although you may not have considered it before, a flat roof covered in grass and plants is a quirky and very efficient way of insulating and protecting your home. Green flat roofs have increased insulation because of their thickness and also keep your home cool in summer. Although they reduce your energy costs and being environmental, they can be expensive to install as the roof may require fortifying to deal with the extra weight. However, they soak up water better and reduce runoff by 50%, reducing the chances of leaking from your flat roof. Green roofs are said to last twice as long as a normal roof because of this.
You may want to consider a “cool” flat roof if you live in a hot area. The dark, heat-absorbing materials such as tar and asphalt usually used in constructing a flat roof can soak up the heat from the sun and transfer it down to your home. A cool roof is made by applying a reflective coating and can reduce the summer cooling costs of your home by 70%. You will also get a tax break if your cool roof meets Energy Star standards.
Flat roofs are sensitive to human traffic and can split or crack if they are trodden on, leading to leaks. When having a flat roof installed, it is highly recommended that you hire a certified professional to ensure your roof is safe and efficient.
GRP flat roofing
GRP is a popular flat roofing material, and it is commonly used to ensure flat roofs remain leak-free and up to scratch.
What is the difference between GRP and fiberglass?
GRP (Glass Reinforced Plastic) is the technical name for what is more often known as fiberglass. It was originally developed back in 1938 for use in insulation. However, it is now used for a variety of purposes in many different industries. Also sometimes referred to as FRP (Fibre Reinforced Polymer), GRP is extremely versatile, hard-wearing, and waterproof. These qualities make GRP perfect for use as a roofing material. If you are concerned about GRP’s appearance, then rest assured: it can be made in a range of different color options. It can also have special finishes applied, such as a non-slip surface. This all means that GRP is now a feasible alternative to more conventional roofing materials.
How long will a GRP flat roof last?
Many tests and research have been carried out regarding the life expectancy of a GRP roof, and studies have estimated that they can last somewhere more than 50 years. This is proven because many glass fiber laminates, which were manufactured back in the 1940s, are still used today. Research has shown that GRP doesn’t really deteriorate; in fact, it has remained in the same condition throughout the testing periods that have been trialed. Some experts would even argue that GRP products applied by a specialist company could potentially last a lifetime.
What colors does GRP come in?
Thanks to advances in recent technology, GRP can be manufactured in different colors, with something to suit every need.
What are the benefits of GRP for flat roofing?
Whilst GRP is a useful material for all roofs; it is particularly beneficial to flat roofs because:
Easy installation: GRP products are cold-laid (this means that they do not require any type of heat treatment and can just be laid as they are). This eliminates a certain level of risk to both the GRP roofing installers and anybody else on the site.
Low insurance: because GRP roofing systems are cold-applied, they do not attract the high levels of insurance premiums that other roofing materials which require hot installation do.
Durable & waterproof: GRP flat roofs are not only very durable, but they are also 100% waterproof; this gives them the edge over other materials that may have traditionally been used for flat roofing.
Low maintenance: Due to the nature of GRP, the entire GRP area of the roof is one huge GRP membrane; this eliminates the need for seam joints or welds, along with the consequential maintenance.
UV resistant: GRP roofing is entirely UV resistant.
Adaptable: GRP forms a very adaptable roofing system, which easily allows for new features such as balconies or a walkway on the roof area. You could also easily add extras such as roof lighting.
Leak-free: The overall and largest benefit of having a GRP roof installed, however, is that as long as it is correctly fitted, it should remain leak-free for life. A particular advantage to those with flat roofs, who may encounter leaks more frequently.
Can GRP be fire retardant?
If fire safety is a must in your household, then you can use GRP, which is formulated with special fire-retardant resins and topcoats.
What does the result look like?
The result can look however you choose, as the surface and color of a GRP laminate can be altered to suit your requirements. You could opt for a smooth or textured finish, as well as choosing from a wide array of different colors.
Is GRP ok in serious weather conditions?
GRP is perfect for those who frequently encounter adverse weather conditions and temperature extremes alike. GRP is often used on boats, which shows that it performs well when put in cold climates and/or rain.
Flat roof repairs & maintenance
If your flat roof needs repair, you will first need to locate the problem. Usually, the first signs of a problem in a flat roof can be found in the room directly below; either damp patches or water dripping from the ceiling will be visible. Before climbing up to have a look, though, think about the strength of your flat roof; it is old and has been damp for a while. It could be rotten in areas and very dangerous. You should always hire a professional roofer to inspect and repair your flat roof safely.
A roofer will inspect the condition of the surface of your flat roof, looking for tears, puddles of water (referred to as ponding), holes, or bare patches. The leak could also be coming from blocked drainage around the edges of the roof. If your flat roof is in a deplorable state, your roofer may recommend replacing the roof entirely.
Hire a professional to repair your flat roof, which can be dangerous and cause structural problems if not carried out correctly. Before any repairs are carried out, a professional roofer will make sure the area is clean, remove any chippings, and use a fungicide to get rid of any mold growth. It’s best to carry out repairs after a long dry spell of weather, meaning there is less moisture in the roof. Below is a guide to how a professional will repair a few basics in your flat roof:
Blisters in the felt
A roofer will clean the surface over and around the blister, ensuring there are no chippings there and ensuring all mold and dirt are removed. They will use a knife to make a cross-cut through the top layer, ensuring not to press down too hard. Peeling back the segments created will allow the roofer to dry the area inside, perhaps using a heat gun. Once that is down, they will apply some bitumen adhesive to the surface and then put the segments back and press down to ensure it stays. The roofer is then ready to apply new pieces of felt, ensuring there’s sufficient overlap to cover the repaired blister.
Splits and tears
If the roofer can lift the split or tear without damaging the felt, they might do that, cleaning the space underneath it. They will then fill the space under the lifted split or tear with adhesive and press it down. Who can fill any larger spaces with bitumen compounds?
You will find the sealing flashing (usually a zinc or substitute strip) where the flat roof touches the wall. The best way to repair this is to use one of the self-adhesive repair tapes. A roofer can do this by cleaning the surface, cutting the tape to length, and then applying it to the area, making sure that the overlaps are well sealed at either end.
Roof Inspection Checklist Before Repairs
A roof inspection works in a preventive way, allowing you to protect your roof from deteriorating while saving you money from expensive future repairs. Adding at least one yearly reminder in your calendar to identify and fix any problems will save you a lot of trouble.
It’s not always easy to tell if your roof needs a complete replacement or just some minor repairs done. Remember, re-roofing is much more expensive than a simple repair. If your roof looks bad, don’t jump into re-roofing planning just yet. Take a look at the chances of possible repairs to put it back in good condition. If you’re not sure whether your roof needs total replacement or just several repairs, you should contact a trusted local roofer about it. This will save you time, money, and effort in the long run.
Flat roof inspection advice
A flat roof needs regular inspection. Good water flows when it rains means that your roof is still most likely in top condition. The usual signs that a roof needs repairing are cracks on the surface and edges. You’ll often be able to tell if your roof needs a total replacement if you’re experiencing any leakage. If you notice this, get help from an experienced roofing company.
Roofing experts can visit your home and help assess the damage to help find the best solution for your home. Another tip for your roof is always to get rid of leaves and random items from piling up at the gutters to avoid uneven weight, as this can distort your roof and lead to unnecessary damage. It’s also a good way to get rid of mosquitoes from setting up an environment there.
Roof Inspection Checklist
The following home roof inspection checklist is not a complete residential roof inspection checklist, but it provides only roofing recommendations to consider.
- Missing roofing caulk used to seal flashing
- Rusty or corroded metal flashing
- Damaged or missing flashing
- Sagging ridges
- Chimney cracks
- Rubber boots at the top of pipes
- Leaking or separated gutter downspouts
- Damaged or rotten fascia board
- Siding above the roof
- Well maintained and working gutters and eaves
Flat Roof Cost