Ballasted mounting systems for flat roof solar installations rely on weight to resist wind uplift without penetrating the roof membrane. Typical photovoltaic (PV) dead loads are between 3-5 lbs/ft2 (14-24 kg/m2), while most installations require between 5-7 lbs/ft2 (24-34 kg/m2). In light wind areas, ballast loads can be as low as 2 lbs/ft2 (10 kg/m2), but in high wind areas, up to 10 lbs/ft2 (48 kg/m2) may be required. Factors such as panel pitch, wind speed, and the structural capacity of the roof can significantly impact the final ballast calculation. Always consult with a structural engineer and choose a modular, adjustable solution, such as that offered by SIC Solar, to ensure safety and cost-effectiveness.

Understanding Ballast and Dead Loads

PV Panel Dead Load

• Standard frame solar panels typically weigh 3-5 lbs/ft2, including the modules and brackets alone.

• For example, a 60-cell solar panel (~17 ft2) typically weighs about 40 lbs, which equates to about 2.4 lbs/ft2; ​​brackets add additional weight.

Ballast for Non‐Penetrative Mounting

• Ballast systems add 5-7 lbs/ft2 (~1.7 m2) of weight to secure solar panels on flat roofs to resist wind uplift.

• In lightweight systems, designers may use only 2-6 lbs/ft2 (~1.7 m2) of concrete or other ballast, especially if wind loads are moderate.

Factors Influencing Ballast Requirements

Wind Speed and Regional Codes

• High wind areas (e.g., design speeds > 100 mph) typically require up to 10 psf of ballast to maintain resistance to uplift.

• Modular grid structures can distribute wind forces to multiple ballast points, resulting in lower unit weights (e.g., Sun Ballast’s Connect system weighs < 20 kg/m2 or ~4 psf on average).

Panel Tilt Angle

• Low tilt angles (<10°) reduce wind uplift forces, resulting in ballast requirements toward the lower end of the range (5 psf).

• The greater the tilt angle, the greater the uplift forces, requiring heavier ballast or mechanical anchors.

Roof Structural Capacity

• Most commercial flat roofs are rated for a live load of 75 kg/m2 (about 15 sq. ft./m2) and must be able to withstand snow accumulation, maintenance access, and a ballasted PV system.

• Prior to installation, a structural engineer must verify that the roof can safely support the dead and live loads, including the additional ballast.

Calculating Ballast Loads

1. Determine PV Dead Load:

   • Use manufacturer specifications (typically 3-5 sq. ft./m.)

2. Assess Wind Uplift Forces:

   • Reference local building codes and ASCE 7 standards, then calculate lift based on PV panel tilt and wind speed.

3. Select Ballast Weight:

   • For low wind speed, low tilt installations, start with 2-6 sq. ft./m. ballast weight.

   • In hurricane-prone areas or at high altitudes, increase ballast to 10 sq. ft. per square foot.

4. Verify Distribution:

   • Ensure ballast is evenly distributed (e.g., grid/mesh system) to avoid point overloading.

5. Consult Engineer:

   • Always have a licensed professional review the final design and ballast calculations.

Best Practices

• Modular Systems: Choose adjustable modular ballast blocks that can be fine-tuned on site.

• Roof Membrane Protection: Use rubber pads or paving blocks under the ballast to prevent membrane damage.

• Maintenance Planning: Allow for clear access and exit points for roof maintenance and inspection.

• Warranty Considerations: Verify that ballast installation does not void the roof warranty—non-penetrating designs typically preserve the warranty.

About SIC Solar

SIC Solar specializes in manufacturing and supplying high-quality PV mounting solutions, including flat roof ballast systems. Its modular design allows installers to adjust the ballast weight based on site conditions, meeting safety requirements and project budgets without overloading the roof structure.