What a residential solar site survey actually needs

Is your survey ready? Check it against the four readers

Tick what your last survey actually captured. Pick a reader to see which items they depend on. The house lights up zone by zone as each one is covered.

The roof: geometry the whole job is drawn on

Every document in the permit set sits on the roof drawing. The designer needs each usable plane measured, not traced: length at the eave and rake, pitch and azimuth. Pitch and azimuth drive the production estimate, and pitch also feeds the engineer's wind and snow check. The AHJ sees the same geometry on the site plan.

Obstructions need a location, not just a photo: vents, stacks, skylights, chimneys, satellite mounts. They decide where modules can go, and they decide whether the fire pathways work. Under the IRC section many jurisdictions adopt for residential PV (R324.6), you will commonly see a 36-inch pathway from eave to ridge and an 18-inch setback on each side of a ridge, rising to 36 inches when the array covers more than a third of the roof area in plan view. Local amendments change these numbers, so check the code cycle your AHJ enforces.

Roofing type, layer count and condition go to the engineer and the AHJ. Tile, metal and comp shingle take different attachments, a second layer changes fastener length, and a roof near the end of its life is a conversation to have before the array goes on, not after.

The attic: the structural input nobody can guess

The structural engineer's job is to show that the existing framing carries the added dead load of the array and the wind uplift and snow load for the site, typically under ASCE 7 as adopted locally. They cannot do that from the outside. The minimum from the attic is member type (rafter or truss), depth, spacing and span between supports, measured on the members under the proposed array.

Add sheathing type and thickness, plus anything that changes the answer: sagging, cracked or notched members, water staining, previous repairs. Note what is in the way of attachments too, such as ducting, junction boxes and equipment, because it decides where the installer can actually land a mount. With no attic access, the survey should say so plainly.

The service: where most redesigns start

Three readers depend on this zone at once: the designer sizing the system, the AHJ checking the interconnection against the NEC, and the utility deciding what it is connecting to.

Main breaker rating and busbar rating, photographed as two separate labels. They are often different, and for a load-side connection the busbar is the constraint. Under the NEC's 120% rule (705.12(B)(3)(2) in the 2020 and 2023 editions), when the solar breaker sits at the opposite end of the bus from the main, 125% of the inverter's output current plus the main breaker rating may not exceed 120% of the busbar rating.

Panel interior with the dead front off: make, model, open and tandem slots, and service conductor size. This decides between a breaker, a supply-side connection, a main-breaker derate or a panel upgrade. Meter number and service type (overhead or underground, meter-main or separate) go on the utility's interconnection application. Grounding and bonding go on the one-line.

Finally, where the new equipment goes and how conduit gets there, with a measured run length. The AHJ wants working clearance in front of new gear (NEC 110.26 sets 36 inches of depth for typical residential voltages). The rapid shutdown initiation device under NEC 690.12 generally has to be readily accessible outside for one- and two-family homes, and many utilities want a visible, lockable AC disconnect near the meter. Whether yours does depends on the utility, so check its interconnection handbook.

Shading: one capture per array area

The designer needs shade to produce a defensible production estimate, and some incentive programs and utilities ask for solar access or TSRF figures with the application. The minimum is a horizon capture from each proposed array area, not one shot from the middle of the roof, because a tree that shades the west plane can be invisible from the east one.

Note near obstructions that only matter in winter, like a chimney or a taller neighbour, and whether each tree is on the property. That decides whether trimming is an option or a fixed loss. The capture becomes a full-year model on our shading analysis page, with solar access, TOF and TSRF per plane.

Site and access: the drawing the crew actually uses

The site plan in the permit set shows the array, the equipment and the property. The minimum capture to draw it honestly: where the equipment will stand, the storey count, ladder points that are safe and level, where material stages, and the clearance to the overhead service drop if a ladder or array is near it. Add anything that will be in the way on install day, like a locked gate, a narrow side yard or low branches.

Homeowner items: the details only the occupant has

Some necessary data is not on the house at all. The designer needs twelve months of usage, or a recent bill, to size the system. The utility application needs the account and meter details as they appear on that bill. Ask about planned loads such as an EV, a heat pump or a battery, because they can change the panel answer. Ask about HOA rules, a planned reroof and any known roof leaks.

For what happens to all of this once it leaves the site, see do solar panels need a permit, which walks through the permit package the survey feeds. The U.S. Department of Energy's homeowner's guide to going solar covers the same steps from the homeowner's side, and the code text itself lives with NFPA 70, the National Electrical Code.

How we cover the minimum

Our site survey puts one technician on the roof, in the attic and at the service panel in one visit, and the deliverable comes back within 48 hours of the visit. The zone pages show what that looks like in the field: roof and drone capture, attic and structure, and electrical and interconnection. The residential overview covers the rest.

Questions installers ask