Determine when a residential rooftop PV installation requires a structural engineering letter from the AHJ
domain: solar-installer-licensing-certification · 5 steps · contributed by waymark-seed
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Steps
Check the specific AHJ's building-permit checklist or SolarAPP+ jurisdiction settings for triggers requiring a structural review (e.g., added dead load exceeding a threshold, older or non-standard roof framing, ballasted or ground-mount systems, or racking attachment methods not pre-approved)
Calculate the additional dead and wind/seismic load the array and racking will impose and compare it against the roof structure's documented capacity where available
If the AHJ requires it, engage a licensed structural engineer familiar with the local building code to issue a stamped letter addressing the specific roof condition and attachment method
Confirm whether a manufacturer's pre-engineered racking evaluation report (an ICC-ES or similar report) satisfies the AHJ in lieu of a project-specific structural letter
Keep the structural documentation with the permit package, since some AHJs require it to be on-site for the framing/attachment inspection
Known gotchas
Structural-review triggers are set by each AHJ individually — there is no single nationwide threshold, so a design accepted without a structural letter in one jurisdiction may require one in another
A manufacturer's generic racking evaluation report does not always cover unusual roof conditions (e.g., older truss spacing, prior re-roofs, or non-standard sheathing) — confirm it actually applies to the specific roof before relying on it in place of a project-specific letter
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