Structural Engineering is a small but critical part of the engineering for a rooftop solar project. It can make or break the feasibility of the project or have significant effects on the system size and cost of racking.
In this article, Pure Power's in-house structural engineering team shares the high level process involved in the structural analysis of a rooftop solar project. We wont get into any calculations, leave that to the professional engineers at Pure Power.
Three Main Steps to Determine the Structural Feasibility:
There are three steps to finalize the structural feasibility for any roof-mounted solar project. In this section, each one of these three steps will be explained in detail.
Structural Element Determination Based on Site Visit Observation.
Increasing Capacity of the Existing Roof Structure to Accommodate the PV System:
There are three basic methods to strengthen structural element to increase its load carrying capacity:
Location of Reinforcement From Inside Building
Current Building Code Requirements:
Almost all states currently adopt International Building Codes (IBC) and International Residential Codes (IRC) with local amendments. Recent editions of IBC (2015 and 2018) dedicated specific sections for roof design with PV panels. It is worth mentioning that prior to 2015, there was no specific guidance for roof-mounted panel loading criteria. The new requirements imposed more complicated loading effects which the roof where the PV panels installed should meet. 2015 IBC and 2015 IRC states the following:
“1603.1.8.1 Photovoltaic panel systems. The dead load of rooftop-mounted photovoltaic system, including rack support systems, shall be indicated on the construction documents.”
“16.12.5.2 Where applicable, snow drift loads created by photovoltaic panels or modules shall be included.”
“R324.4.1 Roof live load. Roof structures that provide support for photovoltaic panel systems shall be designed for applicable roof live load”
“R907.2 Wind Resistance. Rooftop-mounted photovoltaic panel or modules systems shall be installed to resist the component and cladding loads specified in Table R401.2(2).”
Reading the above statements, both snow and wind loads should be included in the load combination now.
Another major code used by structural engineers to identify the applicable loads is ASCE. IBC 2018 adopts ASCE 2016 to determine the loading conditions. The latest ASCE version (2016) now requires the PV panels to be considered as dead load. This can cause major complication in determining the total system weight especially in high seismic regions. Also, live load should not be considered on the roof if the panels were placed at specific distances and heights. All those requirements are relatively new and were ambiguous to the design engineers. Top-rated consulting firms, that have the capacity to involve brilliant structural engineers, can facilitate economical and flowless design for PV panel installation on a roof of any building. A knowledgeable structural engineer who is well-rounded with the current building codes can identify and meet those requirements prior to construction phase, smoothen the design process, and minimize the overall cost of the solar project.