How Does Project Solar Mount Panels on Flat Roofs?

Flat roofs use different mounting equipment for solar than pitched roofs do--there are a couple different options for mounting: Non-penetrating ballasted mounts (weighted), and penetrating/flush mounts. 

Project Solar supports installation on most flat roof types, including rolled composite, thermoplastic membrane, and BUR (Built Up Roofs). 

This article will discuss the following flat roof mounting options:

Non-Penetrating Ballasted Mounts

Illustration of a ballasted mount. With this mount, weights are placed to keep the panels secure on the roof without drilling any holes.

Whenever possible, Project Solar uses non-penetrating equipment to mount on flat roofs. Since flat roofs typically have more issues draining than pitched roofs, using a non-penetrating mount will prevent leaks and help the roof last longer.

These mounts use weights, or "ballast", to keep the equipment in place, and the panels are usually installed at an angle for improved production.

One downside to ballasted mounting is that each row of panels will need to be spaced 18 inches apart to leave space for the weights and mounting hardware.

This prevents the panels from shading each other, since they're elevated, but it can be inefficient for those with limited roof space: more space between rows means less space for panels. 

Tilt/Flush Mounting

Illustration of a tilt-mount. With this mount, panels are attached through sealed anchor screws that are affixed to support beams. 

Project Solar offers penetrating mount options for some flat roof types upon request. However, this option is not available for a few flat roof types, particularly roof types that cannot be easily breached (like sprayed polyurethane foam or built-up roofs).

Most customers who choose this option also choose to tilt the panels (usually towards the south) to gain better solar coverage through the day.

However, we can also install the panels flush with the roof, if desired. With this option, less space is required between the panels, and they can be installed directly adjacent to each other.

This can be beneficial for customers with limited roof space.

Tilt/flush mounts require additional equipment to install, as well as additional sealant. Since they penetrate the roof, measures need to be taken to ensure the mounting holes do not collect rainfall and cause leaks.



Mounts for flat roof projects will have an added cost of $0.24 per watt to account for additional labor and equipment. For more information on roof types, check out this article. 

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