What to Know Before Installing Solar on a New Building

Southern California's rebuilding effort, paired with steady commercial construction activity, means more apartments, retail centers, offices, and industrial buildings are being designed with solar and battery storage in mind from the start. The question isn't whether to include solar, it's how to do it without derailing the schedule or budget. The answer comes down to timing: solar needs to be part of the building's plans from day one, not squeezed in after the fact.

Integrate Solar Design and Installation Into the Building's Plans

Solar is typically permitted under its own separate plan set, but that doesn't mean it can be designed in isolation. Three elements of the building itself, the rooftop attachments, the main electrical panel, and the conduit pathways, must be compatible with the solar system from the outset.

Rooftop attachments

Roof attachments need to match the roof in two ways: structural compatibility and weather-sealing compatibility. Wood rafters, concrete slabs, and metal beams each require different pins and screws, and thick insulation between the attachment point and the structural material can prevent screws from reaching a secure hold.

Weather-sealing also has to be planned in advance. In some cases, attachments are fastened directly to the roof structure before the roof build-up, and get sealed in when the final weather-sealing layer goes on. In other cases, attachments are installed after the roof is complete, which requires hardware designed to be sealed to an existing roof. Deciding which approach fits the project should happen well before the roof goes on, so that attachment installation can be scheduled accordingly.

The main switchboard

The main electrical panel needs enough amperage capacity to accommodate solar, and the simplest way to verify that is the 120% rule (NEC/CEC 705.12(B).3.2). This rule acknowledges that the metal bussing inside a panel can safely carry about 20% more power than its rating suggests. A 400A panel, for example, can handle 80A of solar backfeed on top of 400A from the grid, since 120% of 400A is 480A.

The catch is configuration: solar has to connect to the panel at the opposite end from the utility feed, so the two power sources are spread across the bus bar rather than concentrated in one spot, which can overheat the metal and create a fire risk. Reserve the breaker spot at the far end, typically the bottom, for the solar backfeed breaker, ideally by ordering that breaker as part of the panel itself so compatibility is never in question.

Wire conduits

Solar needs two conduit pathways: one for solar power (typically 1 to 2 inches, depending on system size) running from the roof to the main electrical room, and one for a low-voltage internet connection (typically 3/4 inch) running parallel to it. Both should be routed through the building's interior rather than down an exterior wall.

A hard-lined internet connection is far more reliable than wifi. A majority of solar maintenance requests trace back to nothing more than a weak wifi signal interfering with performance reporting.

Set Aside Enough, and the Right, Space for Solar Equipment

Contractors who aren't used to designing around solar often under-allocate space in the locations that matter most. When that happens, the solar contractor has to redesign and repermit engineered plans, and other trades sometimes have to undo and redo their own work to make room.

The roof

Even a large, open roof can fill up fast once code-required clearances are accounted for. A clear walkway of at least 4 feet is required around the roof perimeter, and that jumps to 6 feet without a parapet or other edge protection at least 3.5 feet tall.

• Clearance around mechanical equipment, roof drains, and hot vents
• Swing radius for window-cleaning davit anchors, which can extend up to 8 feet
• HVAC ducts and plumbing vents that often aren't shown on construction plans but still occupy real roof space

Because solar is installed last, it's the trade that absorbs the impact when other systems aren't coordinated against the space solar actually needs. What looks like a generous allocation on paper can shrink quickly once every other trade has staked its claim.

The electrical room

Every solar system needs a safety disconnect switch within line of sight of, and within 10 feet of, the utility meter, so first responders can shut off solar power along with grid power. These disconnects range from roughly 1.5 by 1.5 feet up to 2.5 by 4 feet depending on amperage and local jurisdiction requirements (LA City, for instance, sometimes requires larger, windowed disconnects).

In many cases, the inverter, the most likely point of failure and the component with the shortest warranty, belongs in the electrical room rather than on the roof, where it stays protected from the elements and extends its functional life. Coordinating that space early, alongside a commercial solar or residential design plan, avoids a scramble later.

Allocate Enough Time for Solar Installation

Solar attachment installation should be scheduled to align with the roof build-up, typically right after decking goes in and before insulation and weather-sealing are applied. Roofs also often need a curing period for adhesives, membranes, and slurries to set, so that time needs a place on the construction calendar too.

Anticipate Changes Between Design and Installation

New construction projects often stretch from schematic design to completion over many months, sometimes a couple of years, and solar is typically the last system installed. During that gap, code requirements evolve, interpretations of those codes shift, and the specific products available at the design stage may no longer be the products available at procurement.

Solar panel manufacturers, for example, gradually shift production toward higher-wattage modules as their assembly lines mature, and lower-wattage options get phased out. Working with a solar company that has strong supplier relationships and visibility into these timelines reduces the odds of a late surprise. Even so, some redesign or repermitting should be expected; jurisdictions and utility plan-checkers aren't always consistent from one project to the next.

There's a lot to plan for when bringing solar and battery storage into a new building, whether the driver is energy savings or a Title 24 requirement. If you're planning a new construction project in Southern California, our team can walk through the details with you; reach out through our contact page to get started.

Frequently asked questions

When should solar be brought into a new construction project?

As early as schematic design. Waiting until the building is fully designed, or worse, until construction is underway, is the most common cause of costly redesigns, repermitting, and change orders.

What is the 120% rule for electrical panels?

It is the code allowance (NEC/CEC 705.12(B).3.2) that lets the combined power from solar and the utility grid exceed a panel's rating by up to 20%, provided the solar backfeed breaker is placed at the opposite end of the bus bar from the utility feed.

How much roof space does solar actually need beyond the panels themselves?

Codes require a clear walkway (typically 4 feet, or up to 6 feet without adequate parapet protection) around the roof perimeter, plus clearance for mechanical equipment, roof drains, vents, and window-cleaning davit anchors, which can have a swing radius of up to 8 feet.

Why does the timing gap between design and installation matter for solar?

New construction can take many months or years from design to completion, and solar is usually the last system installed. Codes, product availability, and panel wattage offerings change during that window, which is why working with a solar contractor who has strong supplier relationships and long-term visibility matters.