Two different questions
People use the words feasibility study and site survey as if they were two names for the same task. They are not. A feasibility study asks whether a project should proceed at all: is there usable roof or land, is the owner interested, does the utility context look workable, and are there any obvious blockers. A site survey asks a narrower and more physical question: what exactly is on this property, measured and photographed, so that an engineer can design it.
Because the questions differ, the inputs differ. A feasibility screen can be done largely at a desk, using aerial imagery, the owner's description of the building, a recent utility bill and whatever drawings exist. A site survey cannot be done at a desk, because the things that decide a commercial project are the things that imagery and drawings cannot show reliably.
What a feasibility screen can and cannot settle
A desk screen is good at eliminating weak candidates quickly. It can show that a roof is mostly covered by rooftop units, that a building is heavily shaded by taller neighbors, or that the usable area is too small to matter. It can flag a building that is clearly a poor fit before anyone drives to it.
What a desk screen cannot do is confirm a project. It cannot tell you the framing type under the deck, the age and condition of the membrane, whether the main switchgear has room for a new breaker or tap, or whether the drawing set still matches the building after years of tenant changes. Treating a passed screen as a confirmed project is how teams end up redesigning after the first site visit.
- Good for the screen: usable area, orientation, obvious shading, building type, rough electrical service size from the owner.
- Needs the survey: structure, roof buildup and condition, penetrations, switchgear and bus details, conduit routes, access and staging.
Why the survey should come before detailed design
Design work built on assumptions is cheap to start and expensive to finish. If the layout is drawn from imagery and then the survey shows a weak bay, a cut joist, an older roof layer or a crowded electrical room, the layout changes and the engineering is partly redone. The survey is the first moment the design team can distinguish what is measured from what is assumed.
A practical rule is to keep design effort proportional to certainty. Before the survey, produce only a concept-level layout labeled as preliminary. After the survey, build the real layout and the plan set on the measured record. The survey-to-plan-set handoff describes how that record maps onto the drawings.
A sensible order of work
1. Screen with remote data
Collect the address, building type, owner contact, utility account details and any drawings the owner can share. Review imagery for usable area and obvious obstructions. Write down the open questions instead of guessing at the answers.
2. Confirm the open questions with a site survey
Send a technician to record the roof surface, the structure, the electrical room and the site logistics in one visit. The list of what to capture is in the commercial rooftop survey checklist. Anything the crew cannot reach should be recorded as not verified, not left out silently.
3. Make the go or no-go call on measured facts
With the survey in hand, the question becomes whether the building as measured supports the project. Sometimes the answer is to reduce the array, change the mounting approach, or move capacity to a carport or ground mount. Learning that after a survey is far cheaper than learning it during construction.
4. Design and engineer from the same record
The structural check, the electrical single-line and the layout should all draw on one record, so that nobody is reconciling three versions of the building.
When a survey can come first
There are cases where skipping a separate screen is reasonable. If the owner has already committed and the building is a known quantity, an EPC may go straight to the survey. If a portfolio of similar buildings is being evaluated, a quick screen of every building and a survey of the strongest candidates is usually the efficient pattern. The point is not rigid sequencing, it is making sure design is never started on facts nobody has verified.
Where Solar Survey AI fits
Solar Survey AI performs the commercial on-site survey in one visit, covering the roof, the structure and the electrical room, with turnaround confirmed when we scope the job. Design and engineering follow from the same record and are stamped by a licensed professional engineer. If you are deciding which projects deserve a visit, talk to us about scoping before you commit crews.