Site Assessment and Shading Survey

Purpose

This produces the measured packet a designer builds from and a crew installs from: roof plane geometry, true azimuth, per-plane solar access, service equipment ratings, conductor route. Half-run, the failures are always the same three: an array laid out on a plane nobody shaded, so production lands under the modeled number and the customer opens a dispute; a busbar rating assumed rather than read, so the interconnection is redesigned after the permit is issued; an obstruction nobody measured, so the crew decides layout by eye at 7 a.m.

The assessor is not designing the system. The assessor is producing measurements another person will be held to.

Scope

Covers residential and light commercial pre-design visits on existing buildings: shading survey, roof plane geometry, electrical service capture, conductor route.

Does not cover roof condition, deck soundness or attachment basis - that is the roof condition assessment SOP, with its own sign-off. Does not cover the interconnection sizing decision; this captures the ratings, and the load-side versus supply-side call is made against the NEC 705 interconnection reference. Does not cover new construction, where planes come off drawings.

Roles and responsibilities

The last handoff is the one that matters. A packet the crew silently works around stops being trusted, and the next assessor gets no signal that their measurements are drifting.

Procedure

1. Confirm access and hazards before leaving the shop. Call and confirm four things: an adult on site, the main panel reachable rather than behind stored goods or a locked gate, the attic hatch clear, any dog contained. Acceptance: all four confirmed verbally and logged on the ticket. Wrong looks like a voicemail and an assumption. Stop rule: no confirmed adult means reschedule, because the panel and attic are inside and half the packet cannot be done from the driveway. Hazard: ask directly about a known leak or soft spot, because a roof someone has already told you is soft is one you survey from the ladder and the eave.

2. Set the ladder and fall protection before anything else. Set the ladder at roughly 4 to 1 with the rails extending at least 3 ft above the roof edge and tied off at the top, per 29 CFR 1926.1053(b)(1) for construction work. Acceptance: no shift under a hand test at the top rail, and the extension above the eave visible from the ground. Residential roof work above 6 ft from a lower level requires fall protection under 29 CFR 1926.501(b)(13); the general-industry trigger is 4 ft at 29 CFR 1910.28, and the split follows the activity, not the building type. Stop rule: no anchor you can use or install means measurements are taken from the ladder and the eave, and the packet is flagged partial rather than filled in from memory.

3. Measure each roof plane. Record pitch as rise over 12 in of run, taken on the deck with a level and rule rather than off a rafter tail; ridge-to-eave and rake-to-rake to the nearest inch; every penetration, vent, skylight and dormer located with two dimensions off a named corner. Acceptance: the plane closes within 2 in when the long side is re-measured from the far end. Wrong looks like one dimension and a guess at the rest, which surfaces later as a layout that will not fit. Stop rule: a plane that will not close gets re-measured before you leave the roof, never corrected at the desk. Hazard: valleys, moss and frost are the slip points, so cross a valley on the ladder or on foam pads, and stay off a wet roof entirely.

4. Take true azimuth per plane, and label the frame. Sight the plane's downslope direction with a compass held clear of racking, conduit and phone, then convert: true azimuth equals magnetic bearing plus east declination, minus west declination. Look up declination for this site rather than carrying the last job's. Acceptance: two readings 6 ft apart agree within 5 degrees, and the recorded value is labeled "true." Wrong looks like a magnetic bearing written into a field marked "azimuth," which walks the whole production model off by the local declination. Stop rule: readings more than 5 degrees apart mean something ferrous is close, so move and re-shoot rather than average two bad numbers.

5. Run the shading survey on every plane you intend to use. Set the shade tool at the expected array center and at each far corner, level it, capture the full horizon. Record monthly and annual solar access percent, the tool's tilt and orientation factor, and total solar resource fraction, which is solar access multiplied by that factor. Photograph each obstruction and classify it: tree (removable, grows back), neighboring structure (permanent), or the building's own chimney or vent stack (relocatable). Acceptance: three capture points per plane and an annual total solar resource fraction at or above 75 percent for the plane to enter the design without further discussion. Treat 75 as a shop default to tune; where an incentive program applies, the binding floor is that program's published minimum, which differs by program and by year. Stop rule: a plane under the floor is neither quietly dropped nor quietly included - it returns to design and sales with the number, the photograph and the named obstruction, and the customer chooses in writing between removing it, accepting the lower yield, or dropping the plane. Hazard: you will be sighting through the tool rather than watching your feet, so brace both feet against a mounted foot block or stand a course lower before raising it.

6. Capture the electrical service without opening anything you do not have to. Photograph the panel rating label, the main breaker handle, the meter and meter number, and the full directory with the dead front on. Record busbar ampacity, main breaker ampacity, make and model, open full-size spaces, and the service entry point. Acceptance: busbar and main breaker ratings each read off a legible label or breaker face, never inferred from each other. Wrong looks like "200 A panel" taken from the main breaker alone when the busbar behind it is rated lower, the most common cause of a post-permit interconnection redesign. Stop rule: an illegible label means the packet records "busbar unverified" and design treats it as unknown. Hazard: pulling a dead front to read a busbar stamp is energized electrical work under 29 CFR 1910.333(b)(2) for general industry and 29 CFR 1926.417 on construction, with PPE per NFPA 70E-2021 in the edition your electrical safety program adopts, so an unqualified assessor does not remove it - an electrician does, on a later visit, and the packet says so.

7. Walk the conductor route and pick the equipment locations. Trace array to inverter to point of interconnection, measure it in feet, and name every transition: attic, exterior wall, garage conduit, penetration through a rated assembly. Record proposed inverter and disconnect locations with a photo and a dimension off a fixed feature, the ambient exposure (a west wall in full afternoon sun derates an inverter and shortens its life), and the monitoring signal measured at that wall. Acceptance: a stated route length, every transition named, signal read at the proposed wall rather than in the driveway. Wrong looks like "route through attic" with no length, which yields a voltage drop calculation built on a guess. Hazard: attic work in afternoon heat is a heat exposure, so run the attic leg early or ventilate and carry water, and step only on joists or laid boards.

8. Close with the customer before you drive away. Walk them to the panel and the proposed inverter wall, show the two or three photographs that matter, and say plainly which planes carry a shading question and what the options are. Acceptance: the customer can repeat back which roof faces are in the design and what the open question is. Wrong looks like "we will send you a proposal," which defers a conversation that gets much harder once a price is attached. Stop rule: if the customer refuses obstruction removal on the spot, record it as a dated decision and design proceeds without that plane rather than modeling it hopefully.

The record this produces

One site assessment packet per address, on the customer record, readable by design, permitting and the crew:

• Per plane: pitch, true azimuth with the frame labeled, dimensions, obstruction map, monthly and annual solar access, tilt and orientation factor, total solar resource fraction, pass or hold.
• Electrical: busbar amps, main breaker amps, make and model, open spaces, meter number, service entry, verified or unverified flag.
• Route: length in feet, every transition, proposed equipment locations, signal reading.
• Photographs: panel label, directory, meter, each plane wide, each obstruction, each equipment location.
• Decisions: any plane held or dropped, the reason, the customer's position, the date.

Design lays out and models from it. Permitting draws the one-line from it. Months later, when production is being argued about, the dated shading capture is the record of what the roof looked like when the promise was made.

A worked pass, including the step that failed

Two-story house, asphalt shingles, two candidate planes. Step 1 clears: adult present, panel in the garage, hatch clear, dog crated. Step 2: ladder set, extension visible above the eave, ridge anchor installed.

Step 3, plane A measures 5:12, 22 ft ridge-to-eave by 31 ft rake-to-rake; re-measuring the 31 ft side from the far end returns 31 ft 1 in, inside tolerance. Plane B measures 5:12, 14 ft by 31 ft, with a plumbing vent 4 ft off the west rake. Step 4, plane A reads 180 magnetic; local declination is 10 degrees east, so true azimuth is 190, and the second reading also returns 180 magnetic. Plane B reads 90 magnetic, true 100.

Step 5 fails. Plane A: three captures, annual solar access 82 percent, tool-reported tilt and orientation factor 96 percent, so total solar resource fraction is 0.82 x 0.96 = 0.79, or 79 percent, above the 75 percent floor. Plane B: annual solar access 71 percent, tilt and orientation factor 78 percent, so 0.71 x 0.78 = 0.55, or 55 percent, twenty points under the floor. The horizon photograph shows why: two mature pines on the neighbor's lot, not the customer's to cut. The stop rule runs, and plane B returns with the number, the photograph, and the note that the obstruction is off-property and therefore not removable by this customer.

Step 6, the label reads 200 A busbar, the main breaker face 200 A, both legible, four open full-size spaces. Verified, no dead front removed. Step 7, route measured at 46 ft through the attic to a west garage wall; that wall takes full afternoon sun, so the packet proposes the north garage wall instead at 52 ft, where the signal reads two bars. Step 8, the customer is told plainly that the east plane is carried by a neighbor's trees and will not be in the design; they ask whether it can be added later, and that goes down as a dated open question rather than an answer.

Outcome: packet returned pass-with-hold. One plane designed, one excluded on a measured number with a named cause.

References

• 29 CFR 1926.501 and 1926.1053, OSHA construction fall protection and ladders; 29 CFR 1910.28 for the general-industry fall trigger.
• 29 CFR 1910.333(b)(2) and 29 CFR 1926.417, safe work practices for energized electrical work, with PPE per NFPA 70E-2021 in the edition your electrical safety program adopts.
• Shade tool manufacturer documentation for capture height, leveling, and the tilt and orientation factor the instrument reports.
• See related: the roof condition assessment SOP, the NEC 705 interconnection point reference, and the 120 percent rule back-feed reference.