Can Solar Panels Be Installed on a Flat Roof in the UK?

Written-by

Janet Richardson

Reviewed-by

Richard Burdett-Gardiner

Updated on

Sep 29, 2024

Can Solar Panels Be Installed on a Flat Roof in the UK?

Solar panels should be an option for everyone, regardless of the size and/or pitch of their roof. Many people with flat roofs decide against solar panels as they do not think they can be installed or will be more expensive. However, they would be wrong to think that. It is actually perfectly possible to install solar panels on a flat roof for around the same price, and this page takes you through how it can be done.

How do Solar Panel Systems Work on a Flat Roof?

Flat roof solar panels are most commonly found on commercial buildings, where the roof is typically large, flat, and weight-bearing. However, it is still common for them to be installed on domestic properties as well. The flat roof solar panel array that is installed uses the same type of solar panel as a traditional system, but certain considerations need to be made.

The array needs to be able to self-clean during rainy weather (pitched) and also avoid damage during strong winds. The installer will take the pitch and orientation of the system into account, making sure that it captures as much energy from the sun as possible. This is where thin film solar cells can come in really useful. They tend to be incredibly flexible and can also be turned into automatic panels.

These move with the sun as the day goes by, capturing as much sunlight as possible as it is always in direct light. While they are less efficient than crystalline-based solar panels, you will be able to generate more power throughout the day with an automatic system as opposed to a stationary one.

This said, automatic or solar tracking systems are fairly rare, and most flat roof solar panel systems are simply normal panels with a metal mounting system that gives the panels a good orientation to capture light from the sun. 

Flat Roof Solar Considerations

In the majority of cases, you can install solar PV panels on a flat roof without there being any problems. However, there are some differences between solar systems on flat roofs as opposed to sloped roofs that you need to consider.:

Suitability of your roof

Not all flat roofs are suitable for a solar panel system. It’s important to check whether you have any drainage, vents, outdoor units, or other structures that may block space or obstruct sunlight to your flat roof solar panel system. Solar panels for flats may also require planning permission. Always check with a qualified solar PV installer that your roof is suitable for solar panels.

More roof space required 

Solar panel systems on a flat roof take up more space. The solar panels need to be spaced out more, so they don’t overshadow each other which means they take up more space compared to a solar panel system on a sloped roof. The solar panels should be at least one metre from the edge as wind forces can be stronger at the edge which could affect the fastening of the panels. Sufficient spacing between the solar panel rows is essential for access as well as to prevent shading from one row onto the next. 
Due to the spacing required for solar panels on flat roofs, you won’t get the same power capacity from the same surface area as you would on a sloping roof. 

Orientation is Important

Because the sun doesn’t stay in the same place in the sky all day but moves from the east to the west, the direction your solar panels face will determine when they collect the most power. Your location in the world and the time of year will also affect the amount of energy your solar panels can harvest. To produce the most energy in the UK, your solar panels should be south facing. Panels facing east or west are thought to be around 20% less efficient. 

Pitch adjustments 

If solar panels were laid flat on the roof, they would be much less efficient than those installed on a sloping roof. This is where your solar installer’s expertise is required. They can solve this problem by mounting the solar panels on metal frames (known as solar panel mounting systems) at an angle. These metal frames can be adjusted to make your flat roof solar panels work effectively. 

As well as orientation, there is also an ideal pitch for solar panels. With a flat roof, solar mounting frames will be used to set up your panels at an angle that’s suitable for catching the daylight they need to generate energy. If you have an adjustable frame, you can alter the angle of your solar panels to make the most of solar energy throughout the year. If, however, you would prefer to set up your panels on the roof and leave them alone, then a 35-degree angle is considered to be the most efficient on average. 

There are now some advanced systems that can be self-tilting on an automated system to maximise their power generation throughout the day.

Water drainage

If a flat roof solar system does not involve a mount, rain can be a problem. Pitch is not only important for increasing efficiency but also for allowing water to slide off the panels. A solar panel system on a flat roof needs special consideration as water collecting on solar panels can cause irreparable damage. You may want to consider installing drainage devices though changing the angle of the solar panels also works. If the pitch is low and you don’t have a drainage solution you will need to check the panels in poor weather. 

Higher costs

Installing solar panels on flat roofs can be more expensive as the solar PV system will need more mounting equipment to ensure the panels are at the required slope. The mounts, drainage solutions, and extra structural supports can add to the cost of your new solar system. But this will vary depending on your roof. The ballasts that secure the solar panels using a weight usually made of concrete, can increase costs. Ballasts can cost around £60 to £120 per kilowatt on average but prices will differ depending on sizes or whether they offer “universal” mounting or only mount certain panel systems.

Moreover, you might need to repair your roof so it can support the weight of the system incurring further costs. However, there may be lower labour costs as mounting brackets on a roof is less expensive and less time-consuming than attaching panels to a sloped roof. 
Ballasts can be around £60 to £120 per kilowatt on average but prices can vary based on sizes and whether they offer “universal” mounting or only mount certain panel systems. They can also be quicker to install making them cheaper in terms of the installation labour costs.

On a more positive note, it’s safer and simpler to install a flat roof solar panel system than solar panels on a sloped roof. No special equipment is required to install them. 

Aesthetics

A solar panel system on a flat roof is aesthetically more discreet. Some homeowners will be happier if their solar panels are not visible from the street which is possible with solar panels on flat roofs. 

Easier maintenance

Solar panel systems on flat roofs are easier to clean as they are not integrated into the structure of the roof, and you can get under and around them. Flat roofs are also easier to access and stand on which is useful for both cleaning and maintenance. However, you might find that your flat roof solar panels require more cleaning as there are more areas where debris, dust, and other environmental hazards can get trapped. If the pitch of the panels is low, it is more likely that you will need to clean them manually.

Take into account wind speed

Because solar panels aren’t lying close to the surface as is the case with solar panels on sloping roofs wind can be a problem for solar panels on flat roofs. It’s important to seek the advice of professional installers who can tell you about the right size of panel, tilt, and spacing to combat wind. Usually, it’s best to use weights to prevent panels from getting dislodged from the roof. Also, having a stable metal frame will help keep your solar panel system secure. 

Take into account the weight of your system

Although ballasts are vital for adding to the balance and stability of your solar system on a flat roof, they are very heavy. They counter the weight of the angled panels and for this reason, are very important. On the plus side, sand, gravel, or cement can be used to steady your panels without making any roof penetrations. Metal frames are also good for a more robust mounting system. 

Unfortunately, there can be a downside to using ballasts and metal frames as your roof has a weight limit. It’s possible that your roof may not have the capability to support excess weight. You should check your roof is suitable before installing a flat roof solar system and also ensure that you have a suitable roof warranty to cover your new heavy installation if you go ahead. 

Easier to remove and upgrade

Because a flat roof is more easily accessed it is easier and cheaper to remove and replace the solar panel system when the system needs upgrading or your system fails. 

What are the Disadvantages of Flat Roof Solar PV Systems?

• The extra stands and ballasts that you may need to secure your flat roof solar panel system can add a considerable amount to the installation expenses.
• Flat roof solar panel systems take up more space as the panels need to be spaced out in order not to overshadow each other. This means that each row takes up more space than a solar panel system on a sloped roof. 
• Not all flat roofs are suitable for solar panel systems. The ballasts and mounting system can be too heavy for the structure of your roof. You also need to take into consideration whether you have any drainage, vents, outdoor units, or other structures blocking the space required or the sunlight required to generate energy. Planning permission can often be required for apartments wanting to install solar panels. 
• Your flat roof solar panel system may need more cleaning as there are more areas where debris, dust, and other environmental hazards can get trapped.

Do you Need Planning Permission for Flat Roof Solar Panels?

In 2023 the government extended permitted development rights for solar panels to allow homeowners with flat roofs to install solar panels without having to obtain planning permission. Now, solar panel installation on flat roofs in the UK generally falls within permitted development rights.

When it comes to getting planning permission for flat roof-mounted systems, the process and terms are actually very similar to those for pitch roofs. Generally speaking, you don’t need to obtain planning permission, provided your installer follows a specific set of guidelines as laid out by your local council. However, before you start any kind of work, it is strongly recommended that you first contact your area’s Local Planning Authority to make sure you are doing everything correctly.

There are some general conditions that your solar panel system must comply with:

• Your solar panel system should be installed in a way that has the least effect on the external appearance of the building and the amenities of the area. 
• Your solar panel system should not protrude more than 0.2 metres beyond the plane of the roof.
• Your solar panel system should not be higher than the highest part of the roof excluding the chimney. 
• If the solar panel system is no longer needed it should be removed as soon as is practical to do so. 

The general rule for solar panels in conservation areas is that they can't be facing the road. If you live in a conservation area, it may be possible to install a solar PV system but there are specific limitations to take into consideration. For example, some planning authorities may permit a solar PV system as long as it is not visible from any public highways. Saying that some councils are more relaxed on this than others. If your property is listed or within the curtilage of a listed property, you will need planning permission and your solar panel system may be declined. 

If you think that you might need planning permission, it’s advisable to contact the National Planning Portal.

Often in the case of a flat roof solar panel system, you will also need to arrange a survey by a structural engineer to make sure that your roof is suitable for solar panels which will incur more cost. It’s worth having a chat with your installer who can explain more about this. 

How much does it Cost to Install Solar Panels on a Flat Roof?

Flat-roof solar panel costs range between £4,420 and £6,340 for a 3-kW system, £6,100 and £8,200 for a 4-kW system, and £7,720 and £9,440 for a 5-kW system. The average home in the UK is usually a 2 or 3-bedroom house with an annual electric consumption of 2,700 kWh according to Ofgem. A 4kW solar panel system can cover 50-74% of the your electricity demands. There are many variables here though, please check out our page on 'How much space do I need for solar panels?'

 

Household Size	System Size	Roof Space	System Cost	Ballast Costs	Total Costs
1 - 2 Bedroom	3kW	20 sq m	£4,000 - £5,500	£420 - £840	£4,420 - £6,340
3 Bedroom	4kW	27 sq m	£5,500 - £7,000	£600 - £1,200	£6,100 - £8,200
4 - 5 Bedroom	5kW	30 sq m	£7,000 - £8,500	£720 - £1,440	£7,720 - £9,940

The estimated prices above are based on 400W to 450W panels per ballast.

You should bear in mind that the prices above do not include any additional components such as a solar battery storage system. 

Solar systems in the UK usually start around the £3500 mark but often reach as much as £20,000. Here’s a case study of a typical house:

What Angle or Pitch do Flat Roof Solar Panels need to be?

Solar panels that have been mounted on flat roofs should usually be titled upwards to ensure that they capture as much sunlight as possible throughout the day. This also helps to keep each of the panels clean, as the rain will wash away dirt and debris from the surface – keeping efficiency levels up.
For this self-cleaning to be possible, panels should be mounted at an angle of at least 10 degrees. Installers will commonly use a device, such as an A-frame, to mount panels at an angle that varies between 20 and 50 degrees. A qualified and professional installer will be able to determine the best pitch for installation on your roof.

Although solar panels in the UK generate the most power when mounted at an angle of between 30 and 40 degrees, facing due south it is not necessarily the best angle to tilt them at for flat roof installations. This is because other factors have to be considered with flat roof mounting. 
The more the panels are tilted, the higher off the roof they will stand. In order to deal with increased wind loads more ballast and stronger frames and fixings will be required which makes installing panels at steeper inclines more expensive. Often the ballast required for panels mounted at 30 degrees is prohibitive. Your roof structure may not be strong enough to take the additional load. 

Another factor to consider is row separation. The greater the mounting angle, the more the space between rows will need to increase to prevent shading. This means that systems with steeper mounting angles will take up more space. If the panels are mounted below 30 degrees, you will not only minimise wind uplift and roof loading but also maximise the number of panels for your roof space. The best compromise is a mounting angle of 10 degrees when taking into account performance, ballast requirement, the area required, and installation cost. 

What Considerations need to be made for the Wind with Flat Roof Solar Panels?

High winds can pose a potential risk to flat roof-mounted solar systems. However, there are a number of options you can use to counter this. There are two methods that are most frequently used to protect a solar system. These are fixing panels to the structure or adding weight to them.
The latter involves fitting ballast frames and heavy slabs to the roof before attaching the solar panels to them. The former, fixing the panels to the structure, involves penetrating the actual roof and securing a support structure and brackets, to which the solar panels are attached. This is a more intrusive method, but some feel that it keeps the array more secure.

At the end of 2023, the UK Government extended the permitted development rights for solar panels on flat roofs. The change now allows UK homeowners to install solar panels on flat roofs without gaining planning permission. The changes, which have been labelled a no-brainer by industry professionals will allow thousands of homeowners the opportunity to install solar panels without the time-consuming process of applying for planning permission. 

Installation Walk-Through for Solar Panels on Flat Roofs

Pre-installation Preparation and Planning 
Firstly, the site needs to be assessed. Your installer will evaluate the roof’s condition and structural integrity to ensure it can support the weight of the solar panels and any stands and ballasts required. A structural engineer may be required to survey the site.
Your installer will check that there are no potential shading issues from nearby buildings, trees, or other obstructions.
They will also calculate your energy consumption to determine the number and size of solar panels required. 

Obtain Any Necessary Permits
Your installer will obtain any necessary permits from local authorities and utility companies. Your installer can advise you on any local rules and regulations.

Design the System
Your installer will calculate how many panels you need based on your energy requirements and the available roof space. Decisions will be made on the best layout considering the optimal tilt and orientation of the solar panel system to maximise solar exposure. The installer will also consider and decide on the type of system required, whether grid-tied, off-grid, or hybrid.

Select Components
The next step will involve purchasing the various components required for your system starting with the solar panels. The solar panels should be chosen based on the system design and your energy needs. Next, an inverter that suits the system needs to be selected. The options include string inverters, microinverters, or power optimisers. If you can it’s always best to Invest in high-quality components to ensure the longevity and performance of your solar power system. Your installer will purchase the appropriate mounting brackets, rails, and other hardware as well as consider using ballast mounts. Ballast mounts are suitable for flat roofs as they avoid penetrating the roof surface. Lastly, your installer will purchase the necessary electrical cables, connectors, and conduit.

Prepare the Roof
Your installer will remove any debris, dirt, or obstructions from the roof surface. Inspect the roof for any damage and repair it if necessary. 

Layout the Mounting System
Your installer is responsible for ensuring proper safety equipment is available and used (harnesses, helmets, etc.). They should always prioritise safety by wearing appropriate protective gear and following electrical safety protocols. They will mark out where the mounting racks will be installed making sure there is even spacing and alignment. The ballast trays or mounting racks will then be placed according to the design layout. Ballast blocks or weights are used to secure the mounting system without penetrating the roof surface. 

Attach Rails to Mounts
The mounting rails are secured to the ballast trays or mounting racks. Your installer will ensure the rails are level and properly aligned. 

Install the Solar Panels
The solar panels are attached to the mounting rails using clamps or brackets. A small gap is left between the panels for thermal expansion and proper ventilation. The electrical components are now connected. The solar panels are connected in series or parallel depending on the system design. The wiring is run from the panels to the inverter, following the manufacturer’s instructions. 

Inverter and Electrical Setup
The inverter is mounted close to the main electrical panel for easier wiring. The solar panel array is connected to the inverter. The wiring is run from the inverter to the main electrical panel, installing a solar breaker in the panel. The entire system is grounded according to local electrical codes and safety standards. 

Testing and Commissioning
A thorough inspection is conducted to ensure all connections are secure and the system is correctly installed. Your installer will test the system to make sure it is generating electricity as expected. They will set up a monitoring system to track the performance of the solar panels and check for any issues or irregularities in the system’s output. 

Maintenance of System
The panels and mounting system will need to be inspected periodically for any signs of wear and tear. The panels will also need to be cleaned from time to time to maintain optimal efficiency. It’s best to schedule an annual check with your installer to ensure the system is working efficiently.

Can you also have Flat Roof Mounted Solar Thermal Systems?

Solar thermal systems can be attached in the same way as a PV system for a flat roof. They will also operate in the same way that any other traditional solar thermal system would, generating heated water for your home. The Renewable Energy Hub has a directory of installation companies that you can use to find a reputable company for your installation, just select solar thermal or solar PV and enter your postcode. 

 

Have you found yourself interested in solar panels? You can search our directory of accredited solar panel installation companies using the form below. Or simply give us a ring using the number at the top of this page, and have a chat.