Flat roofs are typically used on structures for non-standard parts of the living areas.
Popular examples include extensions, garages and outbuildings in gardens. They have a pitch of around 10°.
This article will cover the sorts of costs you can expect to pay for a flat roof as well as other factors which may affect the price of flat roofs.
Flat Roof Cost per m²
The roof cost minus the finishings is roughly £99/m², as broken down below. To get the total flat roof cost, you’ll need to add the base cost (£99/m²) plus the type of finishing, which are given in the second table.
Base Flat Roof Costs
|Item||Labour Cost per m²||Material Cost per m²||Total Cost per m²|
|Ceiling Joists - 150mm x 75mm||£17||£28||£45|
|Plywood - 18mm thick||£13||£14||£27|
|Vapour Control Layer||£1||£1||£2|
|Slab Insulation - 120mm thick Celotex||£6||£20||£26|
Total Flat Roof Costs Including Roof Finishing Layer
|Item||Cost per m²||Total Cost (Base + Roof Finishing) / m²|
|Fibreglass / GRP||£71||£170|
|PVC Gutters||£18 / m|
|Aluminium Gutters||£33 / m|
|Flashings||£35 / m|
|Aluminium Downpipes||£42 / m|
|Flashings||£20 - £35 / m|
Factors That Affect Flat Roof Costs
Flat Roof Specification
Jobs can vary considerably. For example, there may be more additional items needed such as guttering and flashing. Other items that can vary the cost include multiple or complicated trims, ventilation and insulation.
Larger roofs will cost less per m² than smaller ones. Generally over a 100m² would see a 5% reduction in cost.
Costs increase the higher the flat roof is, which is dependant on the storey it’s at. Flat roofs on a 3 storey building will be higher than one a few feet high for example. This is because scaffolding may be necessary at larger heights as well as less accessibility.
Every business has different overheads and expensive, and businesses will factor these into their price different. Skilled tradesmen are more likely to be busy and can charge higher prices.
Although prices above give a good indication of what to pay, it’s not a good idea to always go for the cheapest. Standards can drop considerably if you go for the cheapest price.
Areas in the south of England and London will be higher than in other parts of the country. The prices quoted in the table above apply for the South East or Outer London area. The adjustments below can be used to calculate costs in your area.
Region % Adjustment
South East (Southampton, Oxford, Kent, Outer London) 0
Inner London +4%
South West (Bristol, Exeter) -4%
West Midlands (Birmingham) -10%
East Midlands (Northampton, Nottingham, Leicester) -10%
East Anglia (Cambridge, Norwich, Ipswich) -5%
North West (Liverpool, Manchester) -12%
Yorkshire and Humberside (Leeds, Sheffield) -11%
North East (Newcastle, Sunderland) -10%
Scotland (Edinburgh, Glasgow) -6%
Wales (Cardiff, Swansea) -9%
Northern Ireland (Belfast) -12%
Benefits of a Flat Roof
Flat roofs are one of the most popular roofing systems in the UK. Benefits of installing a new flat roofing system or replacing an existing one include:
- Cost – A flat roof usually takes less time and materials than a pitched roof, making it immediately more cost-effective. In addition, this means that it will cost less to replace when the time comes. This is dependent on the size, materials used, installation technique and whether the roof is for commercial or domestic properties.
- Flexibility – Flat roofs are easy to install on most building types and sizes. Their flexibility helps them move with buildings as they expand and contract naturally without the risk of roof damage.
- Long Lasting – The right system and materials will provide you with a long-lasting, durable roof that will offer protection against extreme weather conditions and harmful UV sun rays.
- Low Maintenance – Once a flat roof is installed, they require very little maintenance. For example, they are less susceptible to storm damage than tile-covered pitched roofs.
- Increase Living Space – A flat roof can provide additional space to enjoy your house or commercial property. Eco-friendly garden roofs offer flexibility by providing a rooftop garden or patio with its own flora and fauna.
- Safety – If any work at height is required, flat roofs are significantly safer than pitched roofs due to their stable gradient. This means there is less risk of slipping and falling.
Disadvantages of a Flat Roof
Flat roofs have some disadvantages, depending on the aesthetic you’re looking to achieve and what type of building the roof is for. They include:
- Aesthetic – While this is purely objective, some do not find flat roofs appealing. In the mid-20th Century, many townhouses, in particular, were built with flat top roofs that some feel lacks the character of pitched roofs.
- Drainage – Flat roofs have a tendency not to drain as well as pitched roofs. The greater the slope on a roof, the faster rainwater runs off it into the gutter. Water congregates in puddles on flat roofs, breaking down the roofing material. Caution should be taken to ensure that all piping and flashing are well sealed to prevent leakage.
- Stability – Depending on the size of the property, flat roofs can be less stable than pitched roofs. Commercial properties, in particular, may require additional structural stability to be built into the building if the roof is to cover a large area.
- Less Scope for Extension – Pitched roofs provide homeowners with attic space, which is not possible with a flat roof. If required, there is no scope for a loft conversion to provide additional living space.
- Less Insulation -The attic space also provides insulation in houses that have sloped roofs. The lack of this space in places with flat roofs means less insulation. This can impact your home’s energy efficiency and expose you to fluctuations in temperatures.
How To Check your Flat Roof for Problems
If you can get onto your flat roof yourself, it’s pretty easy to perform a Do-It-Yourself assessment of whether or not you need to call a roofing contractor in.
Call a contractor immediately if you experience water leaks, internal damage or damp patches, rotting wooding timbers, or any other visible signs of wear.
Leaving a flat roof with one or more of these signs for a significant length of time will increase the damage and the cost to repair the roof. In some cases, the damage may lead to a complete roof replacement being required and impact the house’s structural integrity.
Things to look out for when conducting a visual inspection of a flat roof yourself include:
- Signs of punctures, such as a rusty nail or tree branch.
- Rips and cracks, usually brought about by severe weather conditions, harmful UV sunlight rays and building movements over time.
- Missing or damaged flashing, which is the material that waterproofs roofs at their edges.
- Water forming in puddles can be a signifier of poor drainage
- Water leaks suggest a fault in the roof materials
- Faulty gutters and downpipes could cause water to back up on the roof and cause damage
- No sealing between layers can lead to water seeping through and causing damage
When Does Your Roof Need Repairing or Replacing?
The above checklist will help you understand whether or not you should call a contractor out to repair or replace your roof. However, there are other ways to work out whether you should be budgeting for a repair bill or the cost of a full roof replacement.
Flat Roof Leak
If your flat roof is leaking, the strong likelihood is that the entire roof will need to be replaced. Although it might be possible to patch a leak, this will only be a short-term and very temporary solution.
Your contractor will have to remove material, such as felt, from the surface to check roof timbers and other sources of internal water damage.
In addition, they will need to inspect the overall structure of the building to ensure it has enough stability to hold the replacement. If there is rot in the roof timbers and significant dampness levels or mould are found, additional structural work may be required.
Flooding or Puddles
If you find water congregating in puddles or floods on your flat roof, you must immediately call a contractor. The good news is that this doesn’t necessarily mean your roof needs to be replaced, but it does require immediate attention.
The best-case scenario is that the pitch of your roof requires slight alteration to aid with drainage, which is a relatively simple fix. However, this is dependent on how long the water has been pooling on the roof.
If it has been gathering consistently over a relatively long period, leaking can occur, leading to rotting. This would necessitate a roof replacement and potential structural work.
If you use a flat roof as a roof garden, you’ll want to enjoy some greenery. However, there are some types of vegetation that, if found, will require the services of a roofing contractor.
Plants such as moss, algae, lichen, fungus, mould, and other weeds are often a sign of the water build-up upon which this vegetation thrives. As with water congregation, if caught early enough, you may be able to save yourself the cost of an entire replacement.
Sometimes, however, the vegetation can root itself deeply into the roof. In these cases, a replacement roof would prove more cost-effective as it would prevent the foliage from returning and necessitating another potentially costly contractor call-out.
Cracking and Blistering
All roofs are exposed to extreme weather conditions, from UV rays from sunlight to frost, from rain and hailstones to high winds. Flat roofs will inevitably wear and tear after some time, no matter how durable the materials are.
It will need replacing when cracks, blisters, and stretching become visible on a flat roof. These are commonly seen on rubber-topped flat roofs.
Buildings naturally move, another source of stretching or cracking on a flat roof, particularly on older properties.
Failure to call a contractor when tears, cracks and blisters appear can lead to internal water damage and potentially weaken the building’s overall structure.
Out of Date Roofing Systems
Every technology used in the construction industry advances over time as new materials, techniques, and eco-friendly solutions become available.
The flat-roofing world is no different, with older rubber-style solutions being replaced by more durable, flexible and eco-friendly solutions that are most cost-effective and last longer.
Types of Flat Roofing
Most contractors these days will use one of four flat roofing solutions. Single Ply, High-Performance Felt, Liquid and Green.
Single Ply Flat Roof
Single Ply flat roofs are the most common type of flat roof system used today. They are popular choices for almost any kind of building, including:
- New Builds
- Garage Roofs
- Loft Extensions
It comprises flexible PVC sheets that are completely waterproof thanks to the seamless synthetic polymer welding. They are solid, durable, move with the building and provide good insulation levels.
Single Ply roofing’s popularity stems from low purchase and installation costs, particularly on roofs that will not experience foot traffic, such as roof gardens or terraces.
There are two methods of application, Warm Applied and Cold Applied. The Warm Applied method is the more costly of the two methods.
Felt Flat Roofing
Felt roofs have been a popular choice as a flat roofing system for many years and are used on several types of buildings, which include:
- Loft Extensions
This method consists of multiple layers of the felt sheet being layered to form a thick and waterproof barrier which is then covered with materials to ensure it is fully waterproof.
Felt roofing is a durable solution that offers excellent water and wind resistance and can be applied to flat, pitched or curved roofing.
Small surfaces, such as shed roofs, can be attached to roofs by heavy-duty nails and are simple to apply yourself. Larger surfaces, however, require an expert application and will be installed using the Hot Works method or Cold Works method.
Liquid Flat Roofing
Liquid flat roofing is a highly versatile flat roofing system which is becoming increasingly popular as a solution for high traffic areas, including:
- Roof Terraces
- Extension Roofs
Liquid roofs are applied by a hot-melt or cold-applied method. The hot-melt application creates a single seamless layer that is highly durable and long-lasting. However, it is often used for concrete structures and comes with safety considerations required due to the heat involved. This should only ever be performed by a certified installer.
Cold-applied liquids are much easier to apply due and can be used directly on existing roofing as part of a repair job, making it excellent value for money.
Many new builds now specify cold-applied liquid roofs, and they are very popular in hard-to-access spaces or areas with restricted working, such as on balconies, because of the ease with which they can be installed.
Eco-friendly green roofing is becoming a more popular solution for refurbishments and new builds, particularly in cities where green space can be restricted. These include:
- Pubs and bars
- Apartment buildings
- New builds
As well as providing an eco-system that encourages nature to bloom and that can blend into beautiful natural surroundings in more rural settings, there are several other benefits to be enjoyed from a flat green roof.
A flat green roof improves the aesthetic of the building and also improves the thermal performance of the building. In addition, flat green roofing has improved noise insulation, which benefits the local environment.
What to Look for in a Flat Roofing Contractor
It can be tempting to go with the lowest quote you receive when looking into quotes for repairing or replacing your flat roof. However, it pays to do additional research before signing off on a contractor.
Take time to ask each contractor the following questions to assure yourself that you will receive quality workmanship.
- How much experience do you have in replacing and repairing flat roofs?
- What’s the average cost of a flat roof repair or replacement in your experience?
- Will the old material be removed before the new layer?
- Are there any potential costs not included in the quote?
There are further steps you can take to ensure the quality of your tradesman. Find out what qualifications and accreditations they hold and ask for proof.
Certifications to look out for include:
- City & Guilds
- SMAS Worksafe Contractor
Don’t be afraid to ask if they have customer testimonials that they can share and, if possible, contact previous customers to verify the reviews. Finally, ask for photos or videos of previous jobs they’ve undertaken.
Reputable contractors will be more than happy to share all of these details with you; they want to win your business. If a contractor fails to provide adequate reassurance on any of these points, we suggest you look elsewhere.
While this may result in increased costs in the short term, it will provide you with long-term peace of mind and assurance that you will receive excellent customer service and quality workmanship.
Get Prices On Flat Roofs Near You
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