Direct Load Transfer

TerraGen prepared site-specific design and construction packages that got approval and enabled the installers to assemble the PV system most efficiently.

The Challenge

On occasion, structural challenges or building constraints arise with rooftop solar PV projects. One such example is when there is insufficient load-bearing capability of the roof deck to handle the loads imposed by the solar PV system.

In addition to the weight of the PV system, the concentration of the panel snow load through the base rails into the roof deck can also cause an issue. In these cases, the customer is in jeopardy of having to abandon the project because the roof deck having limited, or no, load-bearing reserve capacity. There are various causes of this, including undersized decking, heavy roofing systems combined with heavy snow loads, or outdated building materials that simply cannot support the dead loads imposed on the structure from the PV system.

The reality is that most mounting systems do not have any flexibility in how the loads are transferred into the building roof structure.

The Solution

TerraGen has experience in overcoming these site restrictions and navigating complex structural challenges to enable the system installation to proceed. In these cases, TerraGen works closely with the customer and the building structural engineer to thoroughly understand all the limitations as well as the
onsite building structure.

On one portfolio in Illinois, TerraGen worked with the building engineer to identify an allowance to load transfer directly over the OWSJ, in circumstances where the joists run parallel with the base rails on the TGR system (north/south). The spacing of the OWSJ was provided in a CAD file and then TerraGen used this to ensure the OWSJ did not exceed the allowable rail spans.

TerraGen’s TGR system is the most flexible flat roof racking system available in the industry. It can accommodate any tilt angle, any row spacing and the substructure spacing is completely flexible. TerraGen was able to match the OWSJ spacing with their base rail spacing to accommodate a direct load transfer into the OWSJ.

The Result

TerraGen has been able to save projects across Canada and the United States with this same challenge.

The one portfolio exampled above of four solar PV projects on a school board consisting of a total of 4737 solar modules and 1,606.94 kWp were able to be constructed, while TerraGen’s customer did not have to incur any building structural reinforcement costs. TerraGen prepared site-specific design and construction packages showing the location and dimensioning of all base rails and load transfer points which gave the building engineer the confidence to approve the installation, and it enabled the installers to assemble the PV system most efficiently.