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Last updated: 01 December 2021

Solar Panels on Flat Roof - Complete Guide!

Flat Roof Solar Panels

Is It Possible to Use Solar Panels on a Flat Roof?

There is an unprecedented trend towards using solar panels in the UK, and many families want to know how they can go solar.

One of the most common questions they ask is whether it’s possible to install solar panels on flat roofs. In fact, flat roofs have now become really common in modern British buildings, while the traditional roof pitch was around 40°-50° in the past.

If you're one of those families who live in a flat-roof building, our answer to your question is a big YES. In this article, we're going to let you know some details about installing solar panels on your roof, especially flat roofs.

Different Roof Pitches for Installing Solar Panels

First, it's good to look at the best roof pitches for installing solar panels to know the pros and cons of each one.

Flat Roofs

As said earlier, flat roofs are among the most common roof pitches in the UK. Installing solar panels on flat roofs has several pros and cons, and fortunately, the advantages outweigh the drawbacks.

Here is why:

Advantages of Flat Roofs for Installing Solar Panels

These are several advantages of installing solar panels on flat roofs:

  • Using less material per square foot and being more cost-effective
  • Simple and fast installation process
  • Less exposure from the street
  • Easier maintenance

Disadvantages of Flat Roofs for Installing Solar Panels

There are also some crucial matters that you need to consider when installing solar panels on your flat roof.

For example, standing water can be a threat and destroy your fixtures sooner, especially if you use poor drainage. Therefore, it's necessary to work with a seasoned technician to make sure you won’t face any issues in the future.

Low-Sloped Roofs

Low-sloped roofs are also common in the UK and can be used to install solar panels. Here are some advantages and disadvantages of these roofs.

Advantages of Low-Sloped Roofs

  • Less roofing materials per square feet
  • Easier and safer installation and repair processes
  • Better drainage

Disadvantages of Low-Sloped Roofs

  • Longer melting process in case you have heavy snow, and as a result, more pressure on fixtures.
  • Building codes of your region in the UK must be strictly followed.

Pitched Roofs

Pitched roofs still exist in the UK and have some pros and cons when it comes to installing solar panels.

Advantages of Pitched Roofs

The slope brings about better run-off for debris, water, and snow. Lower probability of water buildup, which can lead to leaks and mould damage.

Disadvantages of Pitched Roofs

Because of the slope, installing, maintenance, and repair are more challenging and may be less safe and more expensive.

What Roof Material Is Best for Solar Panels?

Solar panels may be installed on almost all types of roof, including:

Metal Roof

Metal roofs have several advantages. For example, they are both environmentally friendly and durable.

Also, the solar array is easily attached thanks to the standing seams, and as a result, the installation process is so easy. This way, the labour cost will be relatively lower and it's a good option for people with a limited budget.

Overall, standing seam metal roofs are the best type of roof for installing solar panels.

Tile Roof

Tiles are produced from a variety of materials such as metal, ceramic, concrete, bituminous, polymer-sand, composite, and stone.

Tar and Gravel

This option is one of the most traditional roof types out there. They are placed on the roof by alternating layers of asphalt or tar and certain supporting elements.
They increase the weight of your structures and make the maintenance process more difficult. Also, it might require more bracing and other materials for installing solar panels.

Other types of materials like Torch Down Roof, Foam, and Wood can also be used when installing solar panels.

Is Planning Permission Needed for Installing Flat-Roof Solar Panels?

Another question homeowners ask is if planning permission is required for installing solar panels on their roofs.

Fortunately, solar panels installation is usually categorized as "permitted development", which means planning permission is not mandatory for most buildings.

General Criteria for Installing Solar Panels

  • Minimal impact on the external appearance of the building and the amenity of the area.
  • Equipment should be immediately removed when you don't need them any longer.
  • You can't install solar panels higher than the highest part of your building's roof (excluding the chimney).
  • Solar panels shouldn't protrude more than 0.2 meters beyond your roof slope plane.

When Is Planning Permission Needed?

There are some situations in which you need planning permission.

Flat Roofs

You'll need planning permission if you want to put solar panels on a flat roof. As you know, solar panels on a flat roof are put in frames to provide an angle towards the sun. This usually necessitates a protrusion of more than 0.2 meters above the roof slope, which is against the "permitted development" rules.

Listed Buildings

Solar panels can be installed on listed buildings, although permission is necessary for any change that might impact the building characteristics as an important historical site.

Conservation Areas

If you're living in a conservation area, you need to become familiar with certain restrictions. Solar PV installation is permitted if only it's not visible from any public roadways. To know more details about solar panel planning permission, you can go through the website of Planning Portal.

Tips for Installing Solar Panels on a Flat Roof

Now that you know the possibility of installing solar PV systems on your roof, it's time to learn some more details about the installation. Remember that the more accurate plan you choose and implement, the more comfortable you'll be in the future.

Here are several tips in this regard:

Consider the Cost of Installing Solar Panels on a Flat Roof

Putting solar panels on a flat roof in different regions of the UK typically costs between £750 and £900 per kW. This is significantly less than the £1,250 per kW cost of installing PV panels of the same size on a sloped roof.

Moreover, the cost of installing solar panels might be different based on a variety of factors, such as the number of PV panels and the mounting method you choose. The point is that the labour cost in flat roof solar panels is considerably low when compared with other types of roofs. Overall, the labour cost will not exceed 10% of the total price of a solar panel system. Look out for solar panel grants in your area as they can help reduce the cost.

Find the Best Angle for Flat Roof Solar Panels

According to a study by Stanford University, a 34° roof tilt angle is the best angle for solar panels in the UK. 

The typical solar panel flat roof angle is between 30 and 40 degrees, in which solar panels have a higher chance of absorbing the sunlight. Also, at this angle, solar panels can be clean easier because rain will wash away debris and grime that may reduce the panel's effectiveness.

Professional installers frequently utilize specialized equipment to mount panels at the proper angle, so make sure you choose a skilled worker to do the job.

Pay Attention to the Way Solar Panels Are Fixed on Your Flat Roof

As mentioned earlier, you need to be careful about the way installers fix PV panels on your flat roof.

On steep rooftops, solar panels are generally installed using a "penetration mount," which involves drilling several holes in the roof to secure the racking that supports the solar panels.

But flat roof solar panel mounting systems are a bit different. On flat roofs, weighted mounting systems or "ballast systems" are common. In such systems, the installation process is done without the need for any holes.

In fact, a flat roof solar panel mounting system sits above your roof using gravity, and this makes the installer's job really straightforward. You can also go for the Bauder roof system, also known as BauderSOLAR, which is a great solution for flat roofs.

It combines the solar PV module and the substructure into a single unit that is fastened to the roof without needing to penetrate the waterproofing of the roof deck.

This guarantees that the roof's integrity is maintained in the installation process. Moreover, it’s extremely light, weighing between 9 and 12.5 kilograms per square meter, depending on the module you’re using.

How to Find the Best Solar Panels in the UK (Cost & Efficiency Guide 2021)

We know that finding the right solar panel supplier might mean investing a lot of time to do research. We want to make this process simpler for you, by providing you with up to 4 quotes from different suppliers in your area. This service is completely free for you and is non-binding. All you need to do is fill in the contact form at the top of the page. We will then get back to you as soon as possible to ask you some further questions, and will then connect you with the most suitable installers. You can rest assured that you get the best quotes on solar panels!

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Hossein Karami Lakeh
Written by Hossein Karami Lakeh, Guest Contributor

Hossein Karami Lakeh is an engineer interested in different aspects of energy, especially renewable energy technologies. He holds a master's degree in mechanical engineering, focusing on thermo-photovoltaic systems. He has written several articles for valid ISI journals, international conferences, and high-authority websites to share his ideas on how to make the world a better place to live.