Calculate the optimal solar system size for a flat roof

Calculate the optimal solar system size for a flat roof

Can you install solar panels on a flat roof? How much is output and cost affected?

Written by Andrew Sendy

Updated August 12, 2021

5 minutes read

Categories: Solar 101, Solar efficiency, Solar financing, Solar incentives, Solar panels, Solar power

House with flat roof

Is solar panel installation possible on a flat roof?

You've been thinking about getting a solar system for your home. You've heard about all the ways it can save you energy, and it sounds like a great opportunity. There's only one problem: you've always heard that solar panels need to be placed at an angle, to catch the sun's rays. And your roof is completely flat. Are you still able to install solar panels on your home?

The short answer is YES…...but there are choices and issues to be considered that aren't necessary for solar panel installation on a pitched roof. 

Can solar panels be installed on a flat roof?


If your roof is in good repair and doesn't have large obstructions around, such as trees, which can block the sun and diminish your energy output, you can certainly install solar panels on a flat roof.

In fact, in some ways, a flat roof can be preferable to a slanted one when it comes to solar installation.

For one thing, the panels are harder to see from the street, preserving your home's overall aesthetic value. There are other benefits too.

When planning solar panel installation on a flat roof, one of the decisions you have to make is whether to mount the panels flat or to use tilt-up mounting equipment to raise the panels to a more normal 25°.

What are the disadvantages of mounting solar panels flat against a flat roof?

There are three disadvantages of laying solar panels flat against a flat roof:

  • They get far dirtier over time, and dirt reduces production;
  • In the Northern Hemisphere, as the position of the sun moves from east to west each day - the path is always across the southern part of the sky. Therefore, panels laid flat are not facing the sun as much as panels are tilted towards the south.
  • Laying solar panels flat can sometimes lead to a voiding of the manufacturer's warranty on the solar panels. The reason for this is that when panels are flat, water sits in the lip between the frame and the glass coating of the module. Given these are only sealed by silicon, similar to what you use in a bathroom to seal out water, this adds to the risk that over 10 to 20 years water may breach the barrier and damage the solar panel.

Is different equipment required to install solar panels on a flat roof?

While you can just lay solar panels down flat against a slanted roof, there is some specialized equipment required to mount solar panels on a flat roof. Angled mounts help with sun exposure and energy output.

When I first started in solar installation ten years ago, I would often lay solar panels flat on flat roofs, something I am reluctant to do now.

There are now a lot of engineered tilt-up racking and mounting systems that can be used to tilt up the panels to an optimal level that cost little more than standard mountings used on a pitched roof.

Is it more expensive to install solar panels on a flat roof?

It can be a little more expensive. The angled mounts that your installer uses adds a small amount to the total cost of the system. However, other factors mitigate that price difference.

For most solar systems, the cost of installation and labor make up around 10% of the total price tag.

But on a flat roof, those costs are reduced because working on a flat roof is inherently more accessible and safer than on a slanted one.

On an angled roof, workers need special safety equipment to do their work without falling off. Plus, roofing materials, such as shingles are likely to come loose during the process.

Neither of these is an issue on a flat roof. Installers can walk around freely, and the materials on flat roofs aren't as likely to sustain damage during installation.

In the end, the price difference between installing on a flat roof using tilt-up mountings or installing on a pitched roof is usually only about $800 for a standard 7 kW residential solar power system.

Calculate the total cost of solar installation for your home!

Is output impacted with a flat roof?

On a typical slanted roof, the angle of the solar panels depends on the angle of the roof and the direction the roof faces.

On a flat roof, you can face your solar panels in any direction and tilt them to any angle you want. This freedom means you can optimize your energy output. By facing your solar panels south and adjusting them to an angle equal to your home's latitude, you can maximize their sun exposure and produce more energy.

Do flat roofs require specialized installers?

Not every company is equipped to install solar panels on a flat roof.

However, if that style of roof is prevalent in your area, then it's likely that many of your local solar installation companies will be prepared to accommodate you. And even if it's not, there are undoubtedly some installers in your area who can help. Find a solar company near you that can accommodate your needs!

Are there risks involved in installing a solar system on a flat roof?

As we've already discussed, installing solar panels on a flat roof is safer than on a slanted one.

But once you have them installed, there are a couple of issues that can arise. One is the issue of dirt. Tilted solar panels are self-cleaning: water runs off, taking most dirt and debris with it. Horizontal panels don't offer this benefit.

The main problem that comes from installing solar panels on a flat roof is leakage. If your panels are installed flat, water can pool on and around them when it rains, causing damage to your roof.

Fortunately, there are plenty of ways to avoid water pooling.

The best solution is to tilt your panels at an angle. Even a tilt of just 3 or 4 degrees can help prevent pooling and keep your system clean.

There are also steps you can take during installation to combat pooling.

By drilling the panels directly into your roof, you can anchor the system into place, which reduces the pooling risk.

You can also use a ballasted system, which anchors the panels using weights instead of drilling.

And there are hybrid systems, which incorporate both methods. Learn what kind of solar installation is best for your roof.

Do panels always need to be tilted on a flat roof?

They don't necessarily have to be. However,  you'll get more energy flowing out of them  if you tilt the panels to the optimum angle. Additionally, due to the damage from leaking that we discussed above, it can be tough to get a warranty for panels with a tilt of less than 2 degrees.

In the end, it's preferable to have your panels installed at an angle. You can even change the degree of incline after installation is complete if you like, to suit your energy output needs. Find out how much energy solar panels could produce for your home.


Having a flat roof doesn't preclude you from having a fully functional solar system in your home.

It can even provide better energy output than a slanted roof (because you can control the tilt) for roughly the same price. Find out more about installing solar panels on your flat roof today.

Author: Andrew Sendy Andrew Sendy LinkedIn

As chairman of Solar Investments Inc and chairman of the largest solar panel installation company in South Australia, Andy is passionate about solar power. With his unique working background he writes on the residential solar industry in America from a unique perspective.