What a commercial solar site survey needs.

Zone 01

The roof: membrane, warranty and everything on it

Start with what the array will sit on and who has to approve it. A roof with eight years left under a twenty-five year array is a future re-roof with the array in the way.

• Membrane type. TPO, PVC, EPDM, modified bitumen, built-up or standing-seam metal. Each takes a different attachment and flashing detail.
• Age and condition. Install date if the owner has it, then blisters, ponding, open seams, soft insulation underfoot and prior patches, photographed and located.
• Warranty holder. Who issued the warranty and whether it is still active. Many manufacturers require an approved roofing contractor to make or inspect new penetrations, so get the contractor's name before design.
• Drainage. Drains, scuppers, crickets and slope direction. Rows and ballast cannot block water paths.
• Penetrations and curbs. Every vent, pipe, hatch, skylight and curb located on a plan, not just photographed.
• HVAC and obstructions. Rooftop units, ductwork, gas lines and their service clearances.
• Parapets. Height on each side. Parapets change wind zones, shading and where snow drifts collect.

Where fire pathways come from

Rooftop access pathways come from the fire code, not the design preference. Under the 2021 International Fire Code, section 1205.3, non-residential roofs generally need a 6 foot clear perimeter (reducible to 4 feet where either building axis is 250 feet or less), interior pathways at intervals no greater than 150 feet, and clear paths to standpipes, hatches and ventilation. Adopted editions and local amendments differ, so the survey should record the jurisdiction and any fire marshal requirements the owner already knows about.

Zone 02

The structure: what the roof can actually carry

This is the zone that imagery cannot see and the one most likely to stop a project late.

• Framing type. Open-web steel bar joists, joist girders, wood trusses, glulam or precast concrete. Record which.
• Depth, spacing and span. Joist depth, center-to-center spacing and clear span between supports, measured, plus any joist designation still legible on the members.
• Deck type and gauge. Steel deck profile and gauge, wood sheathing, or concrete. The deck decides what an attachment can bite into.
• Column lines. Grid spacing and where the heavier girders run. Heavier equipment wants to land near them.
• Existing drawings and as-builts. Ask for them early. Then verify them, because re-roofs, added units and tenant changes drift from the drawings over decades.

Ballasted, attached or both

A ballasted system avoids penetrating the membrane but adds dead load, with more weight at corners and edges where wind uplift is highest. An attached system adds penetrations but much less weight. Many commercial arrays end up hybrid, with ballast in the field and some attachments at the edges, and in higher seismic regions the engineer may require attachment regardless. Which is viable depends on spare structural capacity, so the framing data comes first.

When you need a PE stamp

On commercial rooftops, most jurisdictions require a structural evaluation stamped by a professional engineer licensed in that state, and many require the electrical drawings to be sealed as well. Treat a stamp as the default for C&I and confirm the specifics with the authority having jurisdiction. The engineer checks dead load from the array and ballast, wind uplift, snow load including drift against parapets and the array itself, and seismic, all against the framing the survey recorded. "Depth unknown" means a conservative assumption or a second visit.

Zone 03

The electrical room: switchgear and the point of interconnection

System size is often decided here, not on the roof. A building with a big roof and a small, full switchboard is a small system unless someone plans a supply-side connection or an upgrade.

• Switchgear nameplates. Main switchboard or switchgear manufacturer, bus rating, main device rating and short-circuit rating, photographed legibly.
• Service size and voltage. Commonly 208Y/120 V or 480Y/277 V three-phase on commercial buildings. Record the actual configuration, including any high-leg delta.
• Available fault current. Usually from the utility or an existing study. New equipment needs an adequate interrupting rating.
• Transformer. Pad-mount or vault, kVA and impedance from the nameplate, and who owns it.
• Utility meter and CT cabinet. Meter number, CT cabinet location and whether the utility seals it.
• Space and clearances. Wall and floor space for inverters, AC combiners and disconnects, with the working clearances the NEC requires in front of equipment.
• Conduit routing. The route from array to equipment to the point of interconnection, with lengths, wall penetrations and roof crossings.

Supply-side vs load-side

A load-side connection lands the PV output on a breaker in the switchboard, so it is limited by the busbar rules in NEC 705.12. A supply-side connection taps the service conductors between the meter and the main service disconnect under NEC 705.11 and is not subject to those busbar limits, but it needs physical room, a suitable tap method and utility acceptance. The survey should photograph both options so the engineer can choose.

Rapid shutdown also shapes the layout: NEC 690.12 requires it for PV circuits on or in buildings, dropping conductor voltage within 30 seconds. Ground mounts feeding a building that only houses PV equipment are exempt, and recent editions also exempt non-enclosed structures such as carports. Which edition applies depends on what your jurisdiction has adopted.

Zone 04

The site: access, safety and the people who use the building

• Carports and ground mounts. If the roof falls short, note parking areas, open land, setbacks, underground utilities to locate and drive aisles to keep clear.
• Fire access. Fire lanes, hydrants, the fire department connection and where the pathways meet the roof hatch or ladder.
• Equipment staging. Where pallets of modules and racking can sit without blocking tenants or trucks.
• Crane access. A pad location, reach to the roof, overhead lines and whether the lot can take outrigger loads.
• Tenant coordination. Access hours, escorts, loading dock schedules and when a shutdown for the tie-in is acceptable.
• Utility bills and interval data. Twelve months of bills, the rate schedule and interval data if the utility provides it, so the system is sized to the real load and demand profile.

Fall protection is part of the survey, not after it

A survey on a low-slope roof is work at height. For construction work, OSHA 1926.501 requires fall protection at unprotected edges 6 feet or more above a lower level. For survey and inspection work treated as general industry, OSHA 1910.28 sets rules by distance from the roof edge, with conventional protection required within 6 feet. Which standard applies depends on the work and is worth confirming with your safety lead. Skylights count as holes under both. Record parapet heights, guardrails, anchors and skylight screens so the crew can plan protection before mobilizing.

Zone 05

Deliverables: what the engineering team needs back

A C&I survey is only as good as the package it hands over.

Survey, then design, on one record. The engineering stage uses the framing and switchgear captured on site.

That is the scope of our commercial on-site survey: roof, structure and electrical room in one visit, with the deliverable 48 hours after the survey. C&I design and engineering works from the same record, sealed by a licensed professional engineer and permit-ready six days from the survey. See also Commercial & Industrial, site surveys, permitting and thermal inspection after energization.