Quick answer
Project-specific engineering of PV support members, connections and roofs or foundations using applicable loads, product capacities and adopted requirements.
Answer: Mounting structure design establishes how PV modules, rails, connections and their supporting roof or foundations carry the project’s applicable loads. It combines verified site conditions, product-specific capacities and the jurisdiction’s adopted design requirements. Selecting a rack or obtaining a rail span table is only part of the work: the complete load path, supporting structure and required project documentation still need qualified review.
More than selecting a racking product
The useful starting point is the load path: module to clamps, rails, attachments and building structure, or to posts and foundations. A strong rail does not compensate for an inadequate attachment or supporting member. The mounting structure must be evaluated as a defined configuration rather than as unrelated catalog parts.
For a rooftop project, obtain framing dimensions, spans, material information, connections, roof condition and available records. Verify that records describe the existing structure; original drawings do not eliminate the need to resolve damage or alterations. For ground mounting, geotechnical information and foundation behavior matter alongside the above-ground frame.
A traceable design workflow
- Establish the basis. Record the location, adopted code/edition, project geometry, material and equipment revisions, and required professional documentation. Requirements for seals or independent review depend on the authority and project.
- Determine applicable loads. Equipment weight, wind, snow, seismic and other relevant actions need the correct site and configuration assumptions. ASCE describes ASCE/SEI 7-22 as addressing multiple hazards and load combinations; this does not mean that edition is adopted everywhere.
- Evaluate combinations and load paths. Use the applicable design method consistently. Check uplift, downward and lateral demands, local reactions and global structural effects as appropriate. The largest pressure alone need not govern every component.
- Check members and connections. Assess strength, stability, deflection and the specified connection behavior. Product tables must match the actual configuration and scope.
- Check the support. Roof framing/deck and attachments, or ground foundations and soil, require their own capacity review. Added ballast also imposes loads; it is not simply free uplift resistance.
- Issue coordinated documents. Retain calculations, drawings, component specifications, assumptions and the required approvals for the exact revision being built.
Use a mounting load calculator to document inputs and demands within its stated scope, not as an automatic substitute for this design process.
Read the engineering report’s exclusions
For example, IronRidge’s August 2025 XR100 certification identifies a specific rail system and reference editions. It excludes the structural adequacy of the selected roof attachments, modules and underlying roof members. Its span tables require the stated criteria to be met. This is an example of why a manufacturer report must be read for scope; it is not a recommendation to apply that report to every roof.
A hypothetical single check with demand of 1.2 kN and corresponding capacity of 1.5 kN on the same design basis gives demand/capacity = 1.2/1.5 = 0.80. That ratio describes only the assumed check. It does not prove the whole installation adequate, establish a permissible spacing or replace deflection, interaction and other required checks. Do not compare unfactored demand with factored resistance or mix force with pressure.
Durability and field changes
Retain manufacturer-specific provisions for thermal movement, environmental exposure, material compatibility, waterproofing and maintenance access. There is no universal expansion-joint spacing, corrosion lifetime or deflection limit for all racks.
Installation teams should preserve records of concealed connections and report discrepancies or substitutions for review before affected work proceeds. The engineer or responsible designer must assess changes in geometry, attachments, hardware or ballast. Sales teams should budget the actual investigation and engineering scope rather than promise fixed fees, approval dates or first-submission acceptance.
A layout export can support coordination, but verify the actual software’s structural calculation and document scope before promising automated approval or a certified design.
Frequently asked questions
Is mounting structure design the same as choosing a rack?
No. It also checks applicable loads, connections and the roof or foundations supporting the selected configuration.
Does a manufacturer’s rail report verify the roof?
Not necessarily. Read the report’s exclusions and arrange the missing project-specific checks.
Does every project require the same engineer’s seal?
No. Confirm the project’s professional-documentation requirements with the applicable authority.
What changes require further review?
Changes affecting the design basis, geometry, load path, equipment or support need assessment by the responsible designer.
Related Glossary Terms
About the Contributors
Solar-industry contributor
Nimesh Katariya contributes to SurgePV content concerning solar project workflows. This profile intentionally does not assert certifications, project totals, seminar counts, or technical-review authority without retained verification evidence.
Editorial contributor · SurgePV
Rainer Neumann is credited as an editorial contributor on SurgePV content. This profile does not assert engineering credentials, project totals, software-testing experience, education, speaking engagements, or media citations because independent verification evidence is not retained in the publication record.
