Solar on a Detached Garage or ADU: Several Roofs, One System
A detached garage, an ADU or any other building on the same lot is designed in Cali-Graf — the free solar design app built by Cali Energy, a Los Angeles solar and roofing contractor — the same way as the house: its roof faces are traced on the same aerial image, measured from the same Google height data and filled with the same panel. Fill roof fills every face that doesn't face north on all buildings at once. In the calculation, each face is its own array with its own pitch, direction and shade, and all of them together form one system for one home and one utility meter. The wiring between buildings and any separate permit are not part of the design — those stay with the installer.
When a second roof makes sense
The usual case: the main roof faces the wrong way, is full, or is shaded, while the detached garage faces south. Using both in one design gets the customer the system they need without forcing panels onto weak faces. The sun map — see designing a solar layout on satellite imagery — shows quickly whether the garage roof is actually the better spot — each face's Sun on this face number compares the house and the garage directly.
Tracing the other building
The aerial image covers an area about 70 m (230 ft) across around the home, so buildings on the same lot are on it. Drag the map to the garage or ADU and trace each of its faces with Roof, as on the house; Cali-Graf measures their pitch and direction from Google's heights in the same way. The rules for tracing are the same too: follow the roof edge including the overhang, and trace every face, not only the one that will hold panels. Details on the editor in designing a solar roof layout on aerial imagery.
Only what is on the photo can be traced. A garage or ADU built after the image date has nothing to trace on, so it can't get panels in Cali-Graf; see old satellite imagery in solar design.
Filling both roofs
Fill roof places panels on every face that doesn't face north, on all buildings at once, around fire setbacks, pathways and obstacles. To fill one face — the garage's south slope only, say, or a north-facing face on purpose — select it and press Fill this face with panels. Panels can then be added, moved or removed by hand on any building, and the result card adds up the panels, the kW DC and the share of the roof across all of them.
How it goes into the calculation
| What Cali-Graf does | |
|---|---|
| Each face with panels | Becomes its own array, with its own pitch, direction and per-panel shade |
| All faces, on every building | Form one system |
| The bill | Is calculated for one home and one utility meter |
| The panel | Is the same on every building — the one chosen for the design |
The calculator's Roof section lists every face with its direction and pitch, so the garage faces show up next to the house's. Production is modeled hour by hour for each array, which is why a south-facing garage and an east-facing house can sit in one system without averaging their directions; see hour-by-hour production per roof face.
Because the bill is calculated for one meter, the design fits the common case of a garage or ADU on the main home's service. An ADU on its own utility meter is billed separately, and a single Cali-Graf calculation doesn't split a system between two meters.
Fire setbacks on the second roof
The editor draws fire setbacks on every roof in the design, using the rules chosen for the home. For an ADU, which is a dwelling, that is what the code expects. A detached, non-habitable garage or carport is exempt from the roof-access rules both in California's R329.6 and in the Los Angeles fire department's form for homes — so on such a garage the editor's layout errs toward fewer panels than the code may allow. The plan reviewer has the final say on each job; the rules themselves are covered in how Cali-Graf applies CRC R329.6 and LAFD setbacks.
Adding the ADU's usage
Cali-Graf calculates from the home's past usage and doesn't add future loads by itself. If the customer is building an ADU — or adding an electric car or a heat pump — add an estimate of the extra kWh to the usage before calculating: as a yearly total (last year's total plus the extra), or spread across the bills to keep the home's own seasonal shape. Two things to tell the customer:
- the "today" bill in the result then includes the new load, so it is higher than their current bills;
- for LADWP homes, solar beyond the home's yearly usage isn't paid for, so don't size for loads that may never come.
Whether a new detached ADU must have its own solar under California's Energy Code is a separate question, answered in does my new ADU need solar and solar for an ADU in Los Angeles.
Have a lot with a garage or ADU? Design both roofs as one system and compare it with the house alone.
What stays with the installer
- The permit. A detached building may need its own permit.
- The wiring. Panels on a garage mean a longer wire run back to the main panel, and Cali-Graf doesn't design that part.
- The structure. Cali-Graf isn't a structural design; whether the garage or ADU roof can carry panels is the installer's check.
- The site visit. As with any Cali-Graf design, every roof in it is confirmed on site.
Frequently asked
Can Cali-Graf design solar panels on a detached garage?
Can I put panels on the house and the garage in one system?
Does Fill roof include the garage?
Does Cali-Graf handle an ADU with its own electric meter?
Do fire setbacks apply to a detached garage?
How do I account for a new ADU's electricity use?
Related reading
Sources & methodology
Product facts on this page come from Cali-Graf's own help center and the pages linked below; figures in examples come from the stated inputs. Features, limits and supported utilities change; each was verified October 16, 2026.
- Cali-Graf Help — Panels on a garage, ADU or second building
- Cali-Graf Help — How the roof gets into the calculation
- Cali-Graf Help — Fill the roof with panels
- Cali-Graf Help — Plan for future usage: EV, heat pump, ADU
- Cali-Graf Help — Supported utilities and areas
- California Residential Code 2025 — Section R329.6, roof access, pathways and setbacks
- LADBS / LAFD — Fire Department Reference Requirements for Rooftop PV Systems on One and Two Family Dwellings (Requirement No. 96)
Put the garage roof to work on your next job
Trace the house and the garage or ADU on the same image, fill both and get one system, one bill and one proposal. Free in Cali-Graf, with daily fair-use limits; step-by-step instructions are in its help center.
Prepared by Cali Energy, October 16, 2026. This article is for general educational purposes only and is not legal, tax, financial, engineering, or utility advice. Rates, incentives, codes, permit requirements, equipment specifications, prices, and program terms may change; figures and timelines are estimates, not guarantees. Confirm current requirements with the applicable utility, AHJ, program administrator, manufacturer, or a licensed professional. See our Content Disclaimer. Cali Energy · 19201 Parthenia St, Unit E, Northridge, CA 91324 · CSLB #1032379 (B, C-10, C-39)