Residential Solar Design: Intake to AHJ-Ready Plan Set

Residential solar design runs on a fixed sequence: intake and site data, a remote assessment or a truck roll, roof plane and array layout, structural attachment and load path, then the electrical design that has to satisfy NEC 2023 690.12 rapid shutdown and the NEC 2023 705.12(B)(3)(2) busbar limit. Almost every rejection we see traces back to one of those steps being guessed at instead of measured.

Key takeaways

• Intake quality sets the ceiling on everything downstream. A main service panel photo that shows the busbar rating and the main breaker is worth more than a page of notes.
• A remote assessment can carry the layout. It cannot carry rafter size, spacing and condition – and that is what a structural reviewer asks for.
• NEC 2023 690.12 requires a rapid shutdown function for PV circuits on or in buildings, satisfied either by module-level electronics or by a listed PV hazard control system.
• NEC 2023 705.12(B)(3)(2) is the 120 percent rule and governs the busbar. The 125 percent factor is a different calculation – it sizes the breaker off continuous inverter output current.
• Avila Solar Drafting turns residential plan sets in 2-3 business days, 1-2 business days on Fast Roof. Pricing depends on scope and complexity — current figures are on the solar plan sets page.

What does the residential solar design workflow actually look like?

Six stages, in order: intake, site assessment, roof plane and array layout, structural attachment and load path, electrical design and interconnection, then the permit package. Each stage produces something the next one needs. Skip a stage and the cost does not disappear – it shows up later as a redline, a change order, or a crew standing on a roof waiting for an answer.

Stage	Who owns it	Output the next stage needs
1. Intake	Sales / ops	Equipment models, utility, AHJ, panel and roof photos
2. Site assessment	Field tech or remote	Roof planes, obstructions, rafter data, service details
3. Array layout	Designer	Module count per plane, setbacks, pathways, string map
4. Structural	Designer / engineer	Attachment type, spacing, load path, stamp if required
5. Electrical	Designer	Single-line diagram, conductor and OCPD sizing, interconnection method
6. Permit package	Drafter	Sheet set matched to the AHJ checklist and adopted code cycle

Our residential solar plan sets pick this up at stage three and carry it to stage six. Stages one and two stay with you, because nobody else can see the house.

What site data do you need before design starts?

A complete residential intake is roughly a dozen items, and eleven of them are photographs or model numbers. Turnaround is measured from a complete intake, so an incomplete one does not save time – it moves the delay from your calendar to ours and then back to yours.

• Jurisdiction and utility. The AHJ name and the serving utility. These decide the adopted code cycle, the submittal checklist and the interconnection form.
• Equipment model numbers. Module, inverter or microinverter, optimizer, racking system, and battery if there is one. Not brands – part numbers.
• Main service panel photos. Deadfront off and on, plus the panel label. We need the busbar rating, the main breaker rating, the manufacturer and the available spaces.
• Meter and service entrance. Meter number, overhead or underground, and the conductor path from the meter to the panel.
• Roof photos by plane. One per plane, plus close-ups of vents, chimneys, skylights and existing penetrations.
• Framing data. Rafter or truss size, spacing, span and material, with an attic photo where the framing is accessible.
• Roof measurements. An aerial roof report, an EagleView XML, or dimensioned field measurements with azimuth and pitch per plane.
• Existing loads. Square footage, HVAC, range, dryer, EVSE and any planned electrification, for the service load calculation.

Jurisdictions ask for this in their own words, but the list barely changes. Riverton City, Utah, for example, publishes a residential PV submittal checklist that asks for the module layout and series or parallel configuration, all wire and conduit types and sizes, fuse and breaker ratings, and the roof covering and framing details – and states plainly that it is “Based on 2020 NEC.” Jurisdictions are spread across several NEC editions, so the cycle on the cover sheet has to match the one the reviewer is holding. If you want the field-side version of this list, work from our solar site survey checklist.

Remote site assessment or site visit: which does the design need?

A remote assessment is enough to lay out an array and size the electrical. It is not enough to certify a load path. The dividing line is structure. Aerial imagery and a roof report give you planes, pitch, azimuth and obstructions. They tell you nothing about what is under the sheathing, and that is the part a structural reviewer will not take on faith.

Data point	Remote assessment	Needs eyes on site
Roof planes, pitch, azimuth	Yes – aerial roof report	Only if the report conflicts with reality
Obstructions and setbacks	Yes	Newer vents, satellite dishes, recent re-roof
Shading	Yes – modeling from lidar	Near-field shade from trees on a neighboring lot
Rafter size, spacing, condition	No	Yes – attic access or a framing photo
Roof covering and layer count	Sometimes	Yes for tile, metal and multi-layer comp
Busbar and main breaker rating	No	Yes – panel label photo
Service entrance condition	No	Yes

The practical rule: send a tech when the job needs framing data, a panel label, or a roof covering you cannot identify from an aerial. Everything else can be desk work. Shade and yield modeling belongs on the desk too – that is what Aurora and Helioscope production reports are for, and running them before layout keeps you from designing an array you have to shrink later.

How do you lay out the array on residential roof planes?

Lay out plane by plane, largest and best-oriented first, then subtract for fire access pathways, setbacks, obstruction clearances and shading before you count modules. Designers who count modules first and subtract later end up with a layout the fire marshal deletes on review.

Work each plane in this order:

1. Establish the plane. Dimensions, pitch, azimuth, and the ridge and eave lines the array squares to.
2. Apply access pathways and setbacks. Ridge setbacks and pathway widths are set by the fire code the AHJ has adopted, and they vary. Draw them before modules, not after.
3. Clear the obstructions. Plumbing vents, exhaust fans, skylights, chimneys and their required clearances.
4. Set orientation and inter-row spacing. Portrait or landscape changes rail runs and attachment count on the same plane.
5. Map the strings. Modules per string, plane by plane, checked against the inverter MPPT window at record low and record high ambient.

Step five is where residential jobs quietly go wrong. A three-plane roof with different module counts per plane can produce a string map that models fine at 25 C and violates the inverter maximum input voltage on a cold January morning. Our walkthrough on how to calculate solar string size covers the temperature-corrected Voc math with a worked example. On microinverter jobs the constraint moves instead to branch circuit conductor ampacity and the number of units per branch.

How does attachment and load path work on common residential roofs?

The load path runs module to clamp, clamp to rail, rail to attachment, attachment into structural framing, and framing down to the foundation. Every roof type changes the middle of that chain and nothing else. Attachment spacing is driven by the site wind and snow loads, the racking manufacturer’s span tables, and the framing you actually have.

What changes by covering:

• Composition shingle. The default. Flashed attachments lagged into rafters. IronRidge’s XR flush mount manual, for instance, directs installers to “Slide flashing between 1st and 2nd course of shingles” – a detail that belongs on the plan set, because inspectors look for it.
• Concrete or clay tile. Tile hooks or tile replacement mounts, with the flashing detail called out per manufacturer. Expect broken tile allowances and a heavier dead load on the existing structure.
• Standing seam metal. Non-penetrating seam clamps. The load path then depends on the panel-to-purlin attachment, which has to be documented rather than assumed.
• Low-slope membrane. Either penetrating and flashed by the roofer, or ballasted – in which case the added dead load usually drives the structural review.

Racking manufacturers publish the numbers you build to. The IronRidge XR flush mount installation manual states the system is “Designed and Certified for Compliance with the International Building Code & ASCE/SEI-7” and publishes a system design load rating of 10 PSF downward, 5 PSF upward and 5 PSF lateral. The manual names no edition for either standard, so read that claim against the cycle your AHJ has adopted – IBC 2021 sends structural loads to ASCE 7-16. AHJs then apply their own site criteria on top: Riverton City requires the racking specs to give required support spacing at its local design values of Exposure C, a 105 mph three-second gust and a 43 PSF ground snow load. Feed those figures into the design and the span table answers itself.

Many jurisdictions want the structure signed off rather than argued. Riverton, again, requires a “letter from Structural Engineer with Utah stamp stating that roof will support added load of Solar Panels.” That is exactly what a structural engineering stamp covers, and our guide to when a solar project needs a PE stamp walks through the triggers. If the roof cannot take it, the array moves to grade and the calculation changes entirely – see our ground mount plan sets.

How do you handle NEC 2023 690.12 rapid shutdown on a residential array?

NEC 2023 690.12 states that “PV system circuits installed on or in buildings shall include a rapid shutdown function to reduce shock hazard for firefighters in accordance with 690.12(A) through (D).” On a residential roof there are two practical ways to satisfy it, and the plan set has to show which one you chose.

• Module-level electronics. Microinverters or DC optimizers that reduce controlled conductor voltage inside and outside the array boundary. Enphase’s code compliance brief, for example, describes the PV branch circuit breaker in its combiner acting as the rapid shutdown device “as specified in 2023 NEC 690.12.”
• A listed PV hazard control system. Underwriters Laboratories describes UL 3741 as a standard that “provides a means to evaluate the operation of photovoltaic (PV) hazard control functions that provide a reduced level of shock hazard from energized PV system equipment.” Read the UL Standards and Engagement announcement of UL 3741 before you assume a given AHJ accepts this route – acceptance is not uniform.

Three things the drawings have to carry regardless of method: the array boundary shown on the roof plan, the rapid shutdown initiation device located and labelled, and the equipment listing that makes the claim true. NEC 2023 added an exception for “PV equipment and circuits installed on non-enclosed, detached structures,” which is why a detached patio cover or open carport is treated differently from the house roof – confirm how your AHJ reads it before you rely on it. For the wider article map, see our breakdown of which NEC articles govern a solar plan set.

What does the NEC 2023 705.12(B)(3)(2) 120 percent rule decide?

NEC 2023 705.12(B)(3)(2) is the 120 percent rule: for a load-side connection, 125 percent of the power-source output circuit current, plus the rating of the overcurrent device protecting the busbar, shall not exceed 120 percent of the busbar ampacity, with the PV breaker landed at the opposite end of the busbar from the main supply. It decides, on most residential jobs, whether the interconnection is routine or expensive.

Do not mix it up with 125 percent. The 120 percent figure applies to the busbar. The 125 percent figure applies to the inverter side – continuous output current is multiplied by 125 percent to size the conductor and the overcurrent device. Two different numbers doing two different jobs, and conflating them is one of the more common redlines we see.

A worked residential case:

• 200 A busbar, 200 A main breaker.
• 120 percent of 200 A = 240 A total allowed.
• 240 A minus the 200 A main = 40 A maximum backfed PV breaker.
• A 7.6 kW inverter at 240 V is 31.7 A continuous output, so 31.7 A x 125 percent = 39.6 A, taken to the next standard size as a 40 A breaker. It fits, with nothing to spare.
• Same house, 125 A busbar with a 125 A main: 150 A allowed, minus 125 A, leaves a 25 A breaker – which caps continuous output at 25 A / 1.25 = 20 A, or roughly a 4.8 kW inverter ceiling at 240 V.

Run that arithmetic at intake, not at design. It is the single cheapest check in the residential workflow and it is the one most often skipped, which is why it turns up so often in our list of why solar permits get rejected.

When does a residential job actually need a main panel upgrade?

A main panel upgrade is triggered when the 120 percent math leaves less breaker room than the inverter needs and no alternative connection method is available or accepted. It is a real cost and a second permit line item, so it is worth exhausting the alternatives first.

• Derate the main breaker. Dropping a 200 A main to 175 A frees 25 A of backfeed. It only works if the service load calculation supports the lower main, and some jurisdictions push a derate out of their expedited residential plan into full plan review.
• Supply-side connection. Landing the PV ahead of the service disconnect sidesteps the busbar limit entirely, at the cost of utility coordination and a tap or a fused disconnect on the service conductors.
• Feed-through or subpanel strategy. Sometimes the constrained busbar is not the one the PV has to land on.
• Power control systems. Newer code language is opening this path up. As pv magazine USA reports in its coverage of NEC 2026 changes to power control systems, a PCS “can be set to actively limit the current and loading on a busbar(s) and/or conductor(s),” which “enables connections of power sources with more current than what 705.12 would traditionally allow for load-side connections.” The bare 705.12 in that quote is the load-side allowance at NEC 2023 705.12(B)(3)(2) in the current cycle. Whether the PCS route helps you depends on the cycle your AHJ has adopted and whether it accepts the listing.

Whichever route you take, the plan set has to show the arithmetic. A reviewer should be able to see the busbar rating, the main rating, the PV breaker and the calculation on the single-line without doing the math themselves. Our notes on permitting requirements that catch installers out cover the jurisdiction-specific versions of this.

What labelling has to appear on a residential plan set?

Every required label needs a location on the drawings and a legible detail on a dedicated label sheet – not a generic note saying labels will be per code. Field crews install what the plan shows, and inspectors check the plan against the wall.

On a typical residential PV job that means the rapid shutdown placard and its initiation device marking under NEC 2023 690.56(C), disconnect and equipment marking under NEC 2023 690.13(B), the interconnection and directory markings at the service equipment under NEC 2023 Article 705, and conduit and junction box marking for energized PV circuits under NEC 2023 690.31. Battery jobs add the energy storage markings under NEC 2023 Article 706.

Some jurisdictions are explicit about the format. Riverton City asks installers to “Provide colored detail page of all required labels for all components of PV system.” That is a good default even where it is not demanded: one sheet, every label drawn to scale with its text, and a keyed location on the site or roof plan. It costs nothing at design time and removes an entire category of correction. If you want a benchmark for what a well-built sheet set looks like, we wrote one on how to judge solar plan set quality.

What does the AHJ-ready package contain?

An AHJ-ready residential package is a sheet set that matches the jurisdiction’s own checklist, cites the code cycle that jurisdiction has adopted, and answers the structural and interconnection questions before the reviewer has to ask them. The sheets themselves are the standard ones – cover, site plan, roof plan, structural details, electrical plan and single-line, label detail, and equipment specifications.

Rather than repeat the anatomy here, we broke down every sheet and what belongs on it in what is included in a permit-ready solar plan set. Read that alongside this workflow: this piece is how the information gets gathered, that one is how it gets drawn.

One caveat on automated permitting. The Department of Energy describes SolarAPP+ as “a web-based platform that automates solar permitting for local governments and other authorities having jurisdiction” covering “residential solar and solar+storage systems.” Where your AHJ uses it, the review is instant – but the compliance work does not go away, it moves forward into the submission itself, and the inspection still happens. Before you submit anywhere, run the design against our checklist for whether your solar project design is ready to submit.

How Avila Solar Drafting handles residential plan sets

You send the intake; we return a stamped-ready sheet set built to the code cycle your AHJ has adopted, in 2-3 business days, or 1-2 business days on Fast Roof. Pricing depends on scope and complexity — current figures are on the solar plan sets page. Revisions are free for six months from the order, and we guarantee accurate solar plan sets – the plans are designed to pass first-time review. You submit them; we do not submit on your behalf.

Residential jobs rarely stay purely PV. Battery backup, a load-side or supply-side interconnection redesign, an EV charger permit design on the same service, or a standby generator plan set with an automatic transfer switch all land on the same panel schedule and the same load calculation. Scoping them together at intake is cheaper than three separate permits and three separate service load calculations. For the code detail behind each, see Level 2 EV charger permit plans and generator permit plans.

Frequently asked questions

Hand off the residential drafting

The bottleneck on most residential pipelines is not sales and it is not the crew – it is the gap between a signed contract and a permit-ready sheet set. Avila Solar Drafting returns residential plan sets in 2-3 business days, 1-2 on Fast Roof, with six months of free revisions and a guarantee of accurate solar plan sets. Start a job on the plan set order form. If the project is unusual – a tile roof with marginal framing, a constrained busbar, a mixed PV and storage service – call 971-410-0655 and we will scope it before you order.