Block ip Trap

The Unknown Perils of Ballasted Solar Systems

15 Jul 2020

By Kevin Kervick

Most commercial solar rack systems are designed around ballast as the preferred method for securing a commercial rooftop solar array.  While ballasted systems offer many benefits, solar installers and designers should carefully review all the variables before specifying the securement method. This includes knowing what type of commercial roof is installed, as well as how that system was installed.

Most companies and installers will tell you that they prefer ballast over a mechanical anchor to preserve the roof warranty.  However, many industry veterans do not realize that ballasted systems can easily void roof warranties, do not eliminate rooftop rack movement, and can create more problems than they solve.

Factory Mutual and Solar

Factory Mutual Approvals (FM Approvals) is closely involved with commercial construction techniques, methods, and testing to mitigate risk. “FM Approval” is often considered the gold standard for testing and approving building products and assemblies.

For rooftop solar, FM outlines (in its Loss Prevention Data Sheet 1-15) the installation best practices and requirements for installing a PV array.  

FM on Ballast

According to the best practices referenced above, FM places clear limits on the acceptable slope for a ballasted PV array on a commercial facility. 

“ Install ballasted rigid PV roof-mounted solar panels on roofs with a maximum roof slope of 1/2 in. per foot (2.4°). A higher slope is not recommended for ballasted PV panels as it will decrease frictional resistance to wind forces and increase sliding forces from gravity loads, weakening wind resistance.”

While commercial roofs are frequently described as ‘flat,’ most are designed with some small degree of slope to ensure that the roof does not allow ponding water. Too often, ballasted solar systems are installed on commercial roofs with steeper slopes than FM outlines. This is dangerous and should be avoided - all PV systems are subject to thermal expansion and contraction and will expand/contract with a downhill bias. As a result, it is not uncommon that ballasted systems “walk” downhill over time. 

FM also outlines specific instructions based on whether the roof was fully adhered or mechanically attached. Knowing which method was used to install the roof is critical for the installer and specifier to understand. 

“ Install ballasted, rigid roof-mounted PV panels over fully adhered roof covers. There is no consensus wind design method for installing ballasted PV arrays over mechanically fastened, single-ply roof covers. When a ballasted PV array is proposed over an existing mechanically fastened single-ply roof cover that is relatively new, do one of the following:

  1. Locate the array with a minimum setback distance equal to twice the roof height and fasten each module around each outside edge of each array.
  2. Mechanically fasten PV panels throughout the entire array, such as by fastening each module around each outside edge of each array, and then intermittently fasten the remaining PV modules in the interior of the array at every second module in their long dimension and every third module in their short dimension.

“Fully adhered” refers to a roof system where the waterproofing is adhered to the insulation or coverboard using adhesive or asphalt, which support a 100 percent ballasted PV system. Mechanically attached roof covers (i.e. membrane systems secured with screws and plates) are subject to ‘billowing’ or fluttering during windy periods, which can result in the array being lifted off the roof and sent on an undulating ride. Solar arrays on these roofs should be at least partially anchored to the roof deck, and never exclusively ballasted. 

FM also mandates that related equipment be anchored to the structural deck or members.

“ Anchor all related equipment, such as combiner/junction boxes and conduits, to the roof deck or roof structural members (or inverters to concrete foundations) as required to provide proper anchorage against expected loads. Use mechanical anchors that can be connected to the equipment and to the roof deck or roof framing. The dead weight and resulting frictional resistance for most equipment is not sufficient to resist wind uplift and lateral wind loads.”

Translation: No how much ballast you use, solar arrays can still move around on the roof. This movement – particularly if there is any debris on the roof under the array – can damage roof covers over time, leading to leaks in the roofing assembly. To minimize movement, all commercial rooftop solar systems should include at least some roof-mount anchors that are secured to the structural deck or members, not merely to the roof cover. Roof covers are meant to keep water out of the building envelope, not hold structural equipment in place against wind loads. 


Roofing Warranties 

Either system may violate the warranty. Fully 100 percent ballasted systems don’t get an automatic pass in preserving warranty protection. Always check the manufacturers website for a sample warranty. The language below is typical of the solar warranties in the industry.

Photovoltaic Overburden Additions on XYZ’s Warranted Roof System. 

This warranty expressly requires that any alterations to the roof during the warranty period must be approved by XYZ and performed by an approved/authorized roofing contractor. Therefore, the warranty will be suspended during the installation of any photovoltaic (“PV”) system. To reinstate the warranty coverage, the building owner must provide the following information and abide by the process outlined herein: 

Additional Required Items to be submitted with this form: 

1) Detailed Roof Plan Indicating Scope of Work and PV Location on Roof 

2) Installation and/or Flashing Details 

3) Photovoltaic Overburden Waiver Signed by Building Owner

On an existing XYZ warranted roof system, a post-inspection is required after the photovoltaic installation has been completed. The review and inspection are subject to fees for the project of $XX/ ft2 with a minimum charge of $XX per project.

The term ‘overburden’ pertains to any equipment (PV panels, HVAC, process piping, etc.) installed on a rooftop. Adding a ballasted or anchored PV system qualifies as ‘overburden’, which means the roof system manufacturer must be informed of the proposed installation.  In the sample language above, the roof system manufacturer recognizes that solar installation will most likely not be performed by one of their authorized roofing contractors. As such, they suspend the warranty during installation. In this case, the warranty can only be restored after an inspection. In other words, if a PV system (ballasted or anchored) is installed without first notifying the roof manufacturer, they are no longer obligated to honor the warranty.

All commercial roofing system manufacturers require a post-installation inspection on warranted work. Some may also require a pre-installation inspection. Although layering additional costs on a solar installation makes it harder to attain an attractive ROI, solar installers should insist on a pre-installation roof inspection, even when not required. Any roof repairs should be completed before panels are installed; if a system is installed over existing roof damage, the installer may be blamed for causing the damage. A pre-installation inspection by the warranty issuer is good protection for both the building owner and the solar installer.

Double Check

If pre-installation notice is not filed with the roof manufacturer, even a 100 percent ballasted system will void the warranty. Many roof warranties have been endangered because the building owner was unaware of the warranty requirements, and the PV installer decided to not raise the issue. If a building owner is concerned about preserving the roof warranty, be sure to get a copy of it to review. Most roof system manufacturers offer several levels of warranty coverage, and the language varies from manufacturer-to-manufacturer. The only way to preserve a warranty is to review it carefully in advance and make sure to follow the steps outlined.

Using ballast to secure commercial solar systems can be beneficial, but it is critical for the specifier and installer to first understand the existing roof system and how it was installed. Choosing the correct attachment method based on this information can save considerable time, money, and potential headaches down the road.


Kevin Kervick is the solar products business manager for OMG Roofing Products of Agawam, Mass. He is responsible for strategic planning for the solar business, as well as for managing solar sales and product development.

OMG Roofing |


Author: Kevin Kervick
Volume: 2020 July/August