A building owner or tenant asks for rooftop solar two years after occupancy. The answer depends on drawings made before the roof was framed. Suppose the roof was framed for a lighter load. Suppose the conduit has no route and the main panel has no room. A simple installation then becomes a structural review, a coring plan and possibly a service upgrade.
Solar-ready design prevents that, and it is mostly a drawing task. This guide is for general contractors, architects and developers in the United States. It shows what the codes make you reserve and what a careful design adds. It stays on reserving space for future PV. For modeling a real PV layout against the other trades, see the solar BIM coordination guide.
Quick answer. A solar-ready building reserves roof area, a conduit route and electrical space for photovoltaic (PV) panels that arrive later. Code minimums come from optional IECC 2021 Appendix CB (commercial) and RB (residential) where adopted. California Title 24 Part 6 Section 110.10 sets a 15 percent solar zone for many nonresidential buildings. The codes mostly require drawn reservations and documented loads, so conduit, structural margin and equipment space are design decisions.
Sources were checked on 31 October 2026. The International Code Council site (codes.iccsafe.org) was not reachable from our research environment. IECC text below comes from UpCodes viewers of adopted editions, so wording can differ from the ICC base text where a host jurisdiction amended it. California text comes from California Energy Commission (CEC) documents. Where this guide gives practitioner judgement instead of a source, it says so.
What does solar ready building design require, and when does it apply?
A solar-ready building has no PV system yet. It has a roof zone kept clear for one, a drawn route for the wiring and space in the electrical equipment. The California Energy Commission states the limit in its 2025 compliance manual commentary. It says: “There are no requirements to install panels, conduit, piping, or mounting hardware.”
The Montana Department of Environmental Quality says the same about IECC Appendix RB. It requires no wiring, conduit or plumbing and no change to roof design.
Whether any of this applies to your project depends on three gates:
- Adoption. The IECC solar-ready appendices are optional. Each UpCodes page for Appendix CB and RB says the provisions are not mandatory unless the adopting ordinance references them. The National Association of Home Builders (NAHB) says the same of the 2024 edition. Adopted appendices become mandatory. Unadopted ones are not part of the code there.
- Building type and size. Appendix CB targets buildings five stories or less above grade plane. California’s rule for nonresidential buildings covers three habitable stories or fewer.
- Exceptions. Installing PV, heavy shading, or a certification by a licensed design professional can remove the requirement.
Solar-ready is not a solar mandate. California requires PV on many new buildings, and its solar-ready section applies only when a building does not install PV.
What do IECC 2021 Appendices RB and CB require?
Appendix RB covers detached one- and two-family dwellings and townhouses. Appendix CB covers commercial buildings. Both follow the same pattern: show a solar-ready zone, keep it free of obstructions, document roof loads, draw a pathway and reserve breaker space.
| Item | Appendix RB, residential (2021) | Appendix CB, commercial (2021) |
|---|---|---|
| Applies to | New dwellings and townhouses with at least 600 sq ft of roof facing 110 to 270 degrees of true north | New buildings five stories or less above grade plane that face 110 to 270 degrees of true north or have low-slope roofs |
| Zone size | At least 300 sq ft, excluding fire code access and setback areas. Townhouses of three stories or less and 2,000 sq ft or less per dwelling: 150 sq ft in sections at least 5 ft wide and 80 sq ft each | At least 40 percent of the horizontally projected gross roof area, less skylights, occupied roof decks, vegetative roofs and fire code access or setback areas. Each sub-zone at least 5 ft in its narrowest dimension |
| Obstructions and shading | No vents, chimneys or roof-mounted equipment in the zone. Set the zone back at least twice the height of any object to its south, east or west | No pipes, vents, ducts, HVAC equipment, skylights or roof-mounted equipment in the zone |
| Structure | Roof dead and live load design values on the construction documents | Collateral dead load of at least 5 psf in the zone’s gravity and lateral design, plus roof dead and live loads on the documents |
| Roof penetration | Capped sleeve, inside diameter at least 1.25 in., on zones at 1:12 slope or less | Not required |
| Pathway | Conduit or plumbing route from zone to service panel or service hot water system | Conduit or piping route from zone to service panel, storage area or service hot water system |
| Service panel | Space for one dual-pole breaker, labeled “For Future Solar Electric”, at the end opposite the feeder | Space for two dual-pole breakers, for solar and for storage, labeled “For Future Solar Electric and Storage” |
| Storage | None | Floor area at least 2 ft by 4 ft, located under IFC Section 1207 |
| Certificate | Posted near the panel, water heater or another conspicuous location | Same |
Exceptions apply. Both appendices excuse a building with a permanently installed on-site renewable energy system and one shaded more than 70 percent of daylight hours annually. Appendix CB adds two certifications by a licensed design professional. One says solar radiation is unsuitable. The other says rooftop equipment, skylights, vegetative roofs or other obstructions prevent meeting the zone area. We read the commercial text on the UpCodes viewers for Houston, Baltimore and Michigan, which agree. The residential text is from the Washington State residential energy code viewer, cross-checked against the Montana DEQ Appendix RB summary.
Local versions change the numbers. The Denver energy code viewer shows Appendix CB with a 60 percent zone. It sets back any obstruction above the zone by twice its height. Its breaker or disconnect space must allow NEC Article 705 compliance. The other three viewers show 40 percent. The UpCodes page does not mark which words are Denver amendments. Treat your jurisdiction’s adopted text as the only text that counts.
What is the status of these appendices in the 2024 IECC?
Both appendices remain in the 2024 IECC as optional appendices. The UpCodes table of contents for the 2024 IECC (Rhode Island viewer) lists Appendix CB (Solar-Ready Zone, Commercial) and Appendix RB (Solar-Ready Provisions). It also lists new or related appendices: Appendix RL (Renewable Energy Infrastructure), Appendix CJ (Electrical Energy Storage System) and Appendix RD (Electric Energy Storage Provisions). The NAHB guidance on adopting the 2024 appendices says Appendix RL gives the same type of requirements as RB. It also covers R-2 low-rise multifamily buildings.
For commercial work, the 2024 Appendix CB text on the Delaware viewer keeps the 40 percent zone, the 5 ft width and the 5 psf load. It differs from the 2021 text in two ways. It shows one dual-pole breaker space labeled “For Future Solar Electric” instead of two spaces for solar and storage. It also shows no storage-ready floor area. We did not read Appendix CJ or the 2024 text of Appendix RB, so we cannot say where storage provisions went or whether RB changed. Delaware adopts the code with amendments, and the page marks none in this appendix, but we could not compare it with the ICC text. Confirm against the ICC document before you quote the 2024 differences in a basis of design.
The practical question is the same for either edition. Ask the building department which IECC edition is adopted and whether the solar-ready appendix is referenced. Some states go further. A comparison by EcoAction Partners says the Colorado model solar-ready code is mandatory for new buildings. It adds a minimum 200 A busbar rating. IECC 2024 Appendix CB stays optional.
What does California Title 24 Part 6 require for solar ready?
California handles solar-ready in Section 110.10 of the Energy Code, Title 24, Part 6. The 2025 Energy Code applies to permit applications on or after 1 January 2026, according to the CEC. Projects permitted before that date follow the 2022 code, so confirm which edition your permit date puts you under.
We read the 2025 text in the CEC’s 2025 Multifamily Compliance Manual, Chapter 7, which reproduces Section 110.10 with commentary. We read the 2022 requirements in the CEC’s 2022 nonresidential solar training slides. We saw no difference in the figures below between the two. We did not compare the editions word for word, so check the edition on your permit date.
| Item | Section 110.10 requirement (2022 and 2025 text read) |
|---|---|
| Covered buildings | Nonresidential buildings of three habitable stories or fewer (not I-2 or I-2.1), hotel/motel and high-rise multifamily of ten habitable stories or fewer, and low-rise multifamily, in each case without a PV system. Additions that add 2,000 sq ft or more of roof area are also covered |
| Zone size | At least 15 percent of total roof area, excluding skylights, for multifamily, hotel/motel and nonresidential buildings. It may sit on the roof or overhang, on another structure within 250 ft, or on covered parking installed with the project |
| Sub-areas | No dimension under 5 ft. Each area at least 80 sq ft if the roof is 10,000 sq ft or less, or 160 sq ft if larger |
| Fire access | The zone must meet access, pathway, smoke ventilation and spacing rules in Title 24 Part 9 and local requirements |
| Orientation | Steep-sloped roofs: azimuth 90 to 300 degrees from true north. The commentary says the azimuth rule does not apply to low-slope roofs (2:12 or less) |
| Shading | No obstructions in the zone. Any obstruction projecting above it must sit at least twice its height difference away, with an exception for obstructions north of all points of the zone |
| Structure | Roof dead and live loads on the construction documents. The code note says Section 110.10(b)4 does not require collateral loads for future solar |
| Pathways | Construction documents show a location reserved for inverters and metering equipment and a conduit pathway from the zone to the point of interconnection |
| Documentation | The occupant receives the construction documents or a comparable document, along with the compliance documentation |
The exceptions matter as much as the rule. Installing PV rated at 1 W per sq ft of roof area or more removes the requirement. A smaller zone, at least 50 percent of the potential solar zone, is allowed when outside shading cuts annual solar access below 70 percent. The CEC commentary says shading from the building’s own equipment does not count toward that test. Roofs designed for vehicles, parking or a heliport are excused. A solar water heating exception covers hotel/motel and high-rise multifamily, and a demand-response thermostat exception covers multifamily.
Single-family homes carry two extra items. The 2022 text on UpCodes shows a 250 sq ft zone for single-family residences. Section 110.10(e) requires a main panel with a 200 A minimum busbar. It also requires a reserved double-pole breaker space marked “For Future Solar Electric”. The 2022 slides name the NRCC-SRA-E family of forms. The 2025 manual names NRCC-SAB-E. Use the form set for your edition. For the PV mandate and permit forms, see the California Title 24 solar compliance guide and the Title 24 glossary entry.
How do zone size, orientation and shading compare on one roof?
The two codes measure the zone from different bases, so the same roof gives different areas. The IECC subtracts fire access areas and several roof uses before taking 40 percent. California takes 15 percent of total roof area less skylights, and leaves fire access to Part 9.
Illustrative example, not a design. Assume a one-story building with a flat roof of 40,000 sq ft horizontally projected gross area. It has 1,200 sq ft of skylights and no occupied deck or vegetative roof. Assume the roof layout leaves 6,000 sq ft of fire access and setback area. That figure comes from the assumed layout, not a code number. Assume no PV is installed.
| Step | IECC 2021 Appendix CB (unamended) | California Section 110.10 |
|---|---|---|
| Starting area | 40,000 sq ft | 40,000 sq ft |
| Less skylights | 1,200 sq ft | 1,200 sq ft |
| Less fire access and setbacks | 6,000 sq ft | Not subtracted |
| Base for the percentage | 32,800 sq ft | 38,800 sq ft |
| Zone percentage | 40 percent | 15 percent |
| Minimum zone | 13,120 sq ft | 5,820 sq ft |
| Minimum sub-area | Width of at least 5 ft | Width of at least 5 ft and 160 sq ft each (roof over 10,000 sq ft) |
The same roof under Denver’s 60 percent text would need 19,680 sq ft (60 percent of 32,800 sq ft). At that size, rooftop mechanical equipment decides whether the zone fits, so settle the equipment layout before the zone.
Orientation. The IECC appendices key to 110 to 270 degrees of true north, but Appendix CB also covers low-slope roofs whatever the building faces. California’s steep-sloped azimuth range is 90 to 300 degrees, and its commentary exempts low-slope roofs (2:12 or less) from the azimuth rule. Orientation mostly decides pitched-roof projects.
Shading. California and Appendix RB both use a clearance of twice the obstruction height. The Appendix CB text we read for Houston, Baltimore and Michigan has no such rule, although Denver adds it. A parapet, screen wall or penthouse on the south side of the zone is the usual conflict. Put tall equipment on the north side of the zone, where both California and Denver exempt it.
Fire access. The zone sits inside the fire code layout. For the pathway rules and where conduit may cross them, see the solar BIM coordination guide. For the method of netting setbacks out of gross roof area, see the fire setback sizing walkthrough. Take the setback dimensions from the fire code your AHJ adopted, not from a worked example.
What a good design adds. An IIBEC article on solar-ready commercial roofs (Corbel, Ringer and Karras, January 2026) calls a marked zone on the roof plan the minimum threshold. They advise a proof-of-concept layout with the firefighter pathways before the area is fixed, especially when an owner needs a minimum power output. They also advise keeping the zone clear of drains, field seams and penetrations and consolidating rooftop mechanical equipment. Draw that test layout on the roof plan and keep it as a sheet in the set.
How much structural reserve should the roof carry?
The codes ask you to document loads. Only one asks you to reserve any. Appendix CB requires a collateral dead load of at least 5 psf in the zone’s gravity and lateral design. Appendix RB and California require the roof dead and live design loads to appear on the construction documents. California goes further and says in a note that Section 110.10(b)4 does not require collateral loads for future solar. The CEC commentary explains the purpose: when a PV system is installed later, the structural design loads at the time of permitting are known.
That leaves a gap between the code reserve and the load of a real array. This table sets the reference points side by side.
| Load basis | Figure | Source | What it does not cover |
|---|---|---|---|
| Appendix CB collateral dead load | 5 psf | IECC 2021 and 2024 (UpCodes viewers) | Concentrated loads, snow drift, wind, seismic |
| Title 24 Section 110.10(b)4 | No collateral load. Document roof dead and live loads | CEC 2025 compliance manual | Any future PV weight |
| Typical PV panels and racking | About 3 psf of collector area. Ballasted: 4 to 6 psf | NREL/TP-7A2-46078 (2009) | Drift and slow runoff, which NREL says can add many times the static load |
| Owner standard placeholder | 15 psf for the panel weight if the model is not chosen | Port Authority of NY and NJ Solar-Ready Roof Design Manual (June 2025) | Written for that owner’s own buildings, not a code |
The 5 psf code figure sits inside the NREL range for ballasted systems. A ballasted array at the heavy end already exceeds it before drift is counted. For a zone of 13,120 sq ft, the illustrative minimum reserve is 13,120 x 5 psf = 65,600 lb. The NREL report is a 2009 document that pairs with an older edition of ASCE 7, so use it for orders of magnitude only. The IIBEC authors say that ASCE 7-22 increases some design loads, including snow and rain, so check the edition your jurisdiction enforces. See our ASCE 7-22 adoption guide and the ASCE 7-22 glossary entry.
The structural engineer of record decides the actual margin. A useful brief to that engineer contains these items:
- A named load case. State whether the future array is assumed attached or ballasted, and give the uniform psf and any concentrated loads. IIBEC notes that ballast spreads load evenly, stanchions create point loads at each post, and steel dunnage creates heavier concentrated loads.
- Snow drift and ponding. IIBEC advises treating drift from panels as dead load and checking deflection and ponding on roofs that may take ballasted PV.
- Live load with and without PV. The Port Authority manual and IIBEC both ask for the roof to be checked in both conditions.
- A written record. Put the assumed PV weight and layout on the structural notes. The installer’s engineer can then see what the original design assumed.
The cost of the extra margin is a decision for the owner and the engineer. It depends on span, framing and snow load, and this guide does not price it. The commercial roof structural analysis guide covers the evaluation a future installer faces when the design left nothing on record.
How should conduit pathways be designed?
The codes require the route on paper. Appendix CB and Appendix RB require construction documents to show a pathway for conduit or piping from the zone to the service panel. California requires the same pathway and a reserved location for inverters and metering equipment. None of them requires the conduit itself. Appendix RB adds a capped roof penetration sleeve, at least 1.25 in. in inside diameter, for zones at 1:12 slope or less.
Good design settles the route while the structure is still open:
- Run the vertical path early. NREL’s guide advises installing conduit through permanent structures during initial construction, because that is much easier than after completion. It also advises a short metallic run from the roof combiner box to the equipment space, to limit voltage drop.
- Reserve space, not just a line. IIBEC advises allocating and labeling space for conduit in ceiling cavities or vertical chases. It says conduit should not run through roof insulation above the structural deck, and should not be routed through steel deck flutes.
- Fix the penetration points. IIBEC recommends predetermined penetration points. It suggests prefabricated or NRCA-detailed sheet metal enclosures near or within the PV area. It advises avoiding pitch pockets because their sealant deteriorates quickly.
- Decide what stays outside. The Port Authority manual allows exterior conduit only on the roof and runs everything else inside the building. That is one owner’s appearance rule, not a code rule, but it shows the kind of decision that belongs in the basis of design.
- State the sizing assumption. Practitioner judgement, not a code rule: size the sleeve or chase from a written assumption about array size and circuit count. Put that assumption on the sheet.
Because the route crosses ceilings, chases and the roof assembly, it must be drawn on the architectural, structural and electrical sheets at once. Our solar BIM coordination guide shows how to model that route and test it for clashes.
What should the electrical room and service allow?
The codes reserve a breaker position. A good design also reserves the equipment space and the electrical capacity that make the breaker useful.
Code minimum. Appendix RB asks for space for one dual-pole breaker and Appendix CB 2021 for two, labeled for solar and storage. California Section 110.10(c) requires the documents to show a location reserved for inverters and metering equipment. The CEC commentary says this space should be sized for a PV system that could cover the entire solar zone. California single-family homes add the 200 A busbar and reserved breaker space.
What a good design adds. The Port Authority manual is a useful checklist for a larger building. It asks for spare breakers or spaces in switchgear, labeled for future PV connection. It asks for reserved space for distribution equipment, inverters, combiner boxes, monitoring and communications equipment, and utility-required disconnects at grade. Reserved spaces must be accessible and free of conflicts with other systems. Lightning protection and grounding paths are coordinated with future rooftop equipment. NREL adds two points. The inverter and balance-of-system equipment need a location near the panel, with enough clearance in front to meet the NEC. An internet connection should also reach the inverter room for monitoring.
Bus and main ratings. The ratings of the busbar and the main breaker decide how much PV a load-side connection can accept later. Our NEC 705.12 guide gives the 120 percent rule, which is NEC 705.12(B)(2) in the 2023 edition. Its headroom formula is 1.20 x busbar rating minus main breaker rating.
| Panel as designed | Headroom for a load-side PV breaker (A) |
|---|---|
| 200 A busbar, 200 A main | 1.20 x 200 - 200 = 40 |
| 225 A busbar, 200 A main | 1.20 x 225 - 200 = 70 |
This is an illustration of the formula only, not a sizing for any project. A larger bus behind the same main gives the future installer room without a panel change. Larger services have other connection methods, and the NEC 705.12 guide lists them. The NEC text is paywalled, so verify the section against the edition your AHJ enforces.
Electrical room layout, conduit routes and service coordination are MEP drawing work. Our MEP design services cover electrical, mechanical, plumbing and fire protection scope. This method turns the reservation into dimensions:
- Set a target array size for the zone with the owner, and write it down as an assumption.
- Choose an inverter approach, such as a few large units or many small ones, because it changes where the equipment sits.
- Reserve wall or floor space near the service with the clearances from a typical manufacturer datasheet. Replace it with the real datasheet when the product is chosen.
- Mark the reserved space, the spare breaker positions and the conduit entry on the electrical room layout and the panel schedule.
- Label the reservations in the field and record them on the certificate.
What goes in the documentation for a future installer?
The code documentation is thin by design. Appendix CB and RB require the zone on the construction documents. They also require a permanent certificate near the electrical panel, water heater or another conspicuous location, posted by the builder or a registered design professional. California requires the occupant to receive the construction documents showing the zone, loads and pathways. A future installer needs more than that to quote and permit the work.
Use this checklist as a handoff sheet. Items marked “Code” appear in the provisions above. Items marked “Practice” are good practice from the sources cited in this guide, not code requirements.
| Sheet or item | What it shows | Basis |
|---|---|---|
| Roof plan | Solar-ready zone boundary, sub-area dimensions, fire access paths, north arrow | Code |
| Test layout | Proof-of-concept array layout inside the zone with fire pathways | Practice (IIBEC, Port Authority) |
| Structural notes | Roof dead and live loads, design snow load and code edition, the assumed future PV load case | Code for loads, Practice for the PV case |
| Roof details | Penetration points, curbs or enclosures, roofing assembly notes | Practice (IIBEC) |
| Conduit plan and riser | Route from zone to electrical room, chase or sleeve locations, sizing assumption | Code for the pathway, Practice for sizing note |
| Electrical room layout | Reserved space for inverters, metering and disconnects with clearances | Code in California, Practice elsewhere |
| Panel schedule or single-line diagram | Bus and main ratings, reserved breaker positions with labels | Code for the reserved space, Practice for the ratings note |
| Certificate and field labels | Posted certificate and labeled reservations | Code (IECC), Practice (labels) |
| Assumptions note | Target array size, inverter approach, load case, edition of each code | Practice |
| Owner package | Copies of the above delivered at turnover | Code in California |
In tenant buildings, the landlord’s base-building drawings are what a tenant’s installer will receive. The tenant improvement MEP guide shows how teams work from base drawings, which is why the assumptions note belongs in them.
How do you assign the work across the design team?
Each item has one lead and at least one dependency. The architect places the zone and keeps it clear, with input from the mechanical designer on equipment placement. The structural engineer sets and records the load case. The electrical designer draws the route, the reserved space and the panel capacity. The general contractor protects the pathways and labels during construction. The owner sets the target array size. If nobody holds the assumptions note, the reservations drift out of date during value engineering, so name its owner in the basis of design.
Where does Heaven Designs fit?
Heaven Designs provides MEP design and BIM services for architects, general contractors and owners. For solar-ready scope, the work is drawing the electrical room reservation, the conduit route and the panel documentation into the MEP set. It also means coordinating them with the roof layout. The scope, the code editions and the turnaround are agreed at scoping. The adopted code and a qualified local professional govern the final design.
FAQ
Is solar-ready construction required in my state?
It depends on the jurisdiction. IECC Appendices CB and RB apply only where the adopting ordinance references them. California applies Section 110.10 as a mandatory requirement to covered buildings that do not install PV. Ask the building department which energy code edition and which appendices apply on your permit date.
Does solar ready mean the conduit is already installed?
No. The IECC appendices and California Section 110.10 ask for a drawn pathway and a reserved location. They do not require conduit, wiring or equipment. Installing the conduit during construction is a design choice that NREL describes as much easier than doing it later.
How big is a solar-ready zone on a commercial roof?
Under unamended IECC 2021 Appendix CB it is at least 40 percent of the net horizontally projected roof area. Under California Section 110.10 it is at least 15 percent of total roof area excluding skylights. Some local versions are larger, such as Denver’s 60 percent. Subtract fire access areas the way your adopted code requires.
Does IECC 2024 still include solar-ready requirements?
Yes, as optional Appendices CB and RB, with Appendix RL added for other residential buildings. They bind a project only where a jurisdiction references them. The 2024 Appendix CB text we read on one viewer differs from 2021 in its breaker and storage provisions, so read the adopted edition.
Should the roof be designed for the full weight of a future array?
The codes do not require it, and California says explicitly that it does not require collateral loads. Whether to reserve more is a decision for the owner and the structural engineer, based on span, framing, snow and the likelihood of PV. At minimum, record the roof loads and the assumed future load case on the drawings.
Next step
Before the next set goes out, add a solar-ready sheet to the checklist above: zone, load case, conduit route, reserved electrical space and an assumptions note. If you want the reservation drawn into an MEP set, send the project details through the contact page.