Solar PV ready: designing new homes for panels and inverters

Most homes that get solar are not designed for it. The array is quoted after handover, the installer walks the roof, and the design is reverse-engineered from whatever the roof and switchboard happen to allow. The result usually works, but it is rarely the array the owner thought they were buying, and it almost never uses the best part of the roof.

A genuinely solar ready home is a different proposition. The decisions are made early, documented on the drawings, and physically roughed in before linings and sheeting close the building up. Orientation, usable roof area, the cable route, the inverter location and the switchboard capacity are all settled while they are still cheap to change.

This article is about those pre-installation decisions. It is not about how many panels to buy, what a system should cost, or which incentive scheme is running. Those are commercial questions the owner settles with an accredited installer. What you control is whether the building will accept a sensible system without anyone having to cut corners.

What ‘solar ready’ actually means on a new build

The term gets used loosely. On a new build it should mean four things are true: there is a defined area of roof that can take an array without obstruction, the structure under that area can carry it, there is a continuous and accessible route for cabling from roof to switchboard, and the switchboard and metering arrangement can accept the connection.

Notice that none of those four are about the panels themselves. They are building decisions, and every one of them is far cheaper to make at design stage than after practical completion. A cable route that has to be chased into a finished wall, or an inverter that has to be mounted on a wall the owner did not want touched, is a cost that surfaces at the worst possible time — after the owner has moved in and is trying to get a system installed quickly.

The NCC energy efficiency provisions set the broader performance framework for the dwelling, and the Australian Government’s Passive design guidance covers the orientation and shading principles that sit underneath it. Neither tells you where to put the inverter. Both tell you that the building envelope and its orientation are the foundation everything else sits on, and solar is no exception.

Orientation and shading decisions belong at design stage

Roof orientation is effectively irreversible. Once the plan is set and the frame is up, you have whatever roof you have. The Passive design guidance is clear that orientation is the single biggest lever on a home’s thermal performance, and the same logic applies to solar: an array on a well-oriented plane will outperform a larger array on a poor one, every time.

In practice this means the designer needs to know which roof plane will carry the array before the roof geometry is locked in. On a simple hip or gable that is usually the plane facing the equator, but real sites are messier. A neighbouring two-storey building, a mature tree on the boundary, or a proposed second-storey addition all change the shading picture, and shading is not a small effect — it drags down the whole string, not just the shaded panel.

Two practical moves at design stage:

• Nominate the array plane on the roof plan, and check it against the site survey, the neighbouring built form and any vegetation that will still be there in ten years.
• Keep the nominated plane free of other roof furniture. Plumbing stacks, whirlybirds, skylights, evaporative cooler droppers and flue penetrations all fragment an array zone and force the installer into awkward layouts.

If the best plane is unavoidably compromised, that is useful information to have now. It may push the design toward a different roof form, a different ridge line, or a decision to place the array on a secondary plane and accept a lower yield. All of those are design conversations. None of them are possible once the roof is sheeted.

Roof structure, pitch and the load you are asking it to carry

Panels, rails and fixings add load to the roof structure, and that load has to be considered by whoever designs the roof — not assumed by whoever installs the array. On a trussed roof the additional dead load is usually well within capacity, but “usually” is not a design statement. The roof designer needs to know an array is intended so the load case is included rather than discovered.

The pitch matters too. A very low pitch changes how fixings and flashings have to be detailed to keep the roof watertight, and it changes how much self-cleaning the array gets from rain. A very steep pitch changes access for installation and for future maintenance. Neither is a reason to avoid solar, but both should be reflected in the roof design and in how penetration flashings are detailed.

Where the roof is steel-framed, the same thermal bridging issues that affect the rest of the envelope apply at the array fixings and at any penetration. If you are working with steel framing, the fixes set out in our article on thermal bridging with steel framing are worth reviewing alongside the solar rough-in, because the two problems are solved at the same stage.

The cable route is the item builders most often leave too late

Ask any solar installer what slows a job down and the answer is usually the cable run. Getting DC and AC cabling from the roof space to the switchboard through a finished house is slow, invasive and expensive. Through an unlined frame it is an hour’s work.

The route needs to be continuous, protected and accessible. That generally means a conduit or a dedicated cable path from the roof space down to the switchboard location, with draw wire installed and capped at both ends so it is not filled with debris or mortar during the rest of the build. It needs to avoid areas that will be inaccessible after lining, and it needs to respect fire separation requirements where it passes through or between fire-rated elements.

Where the cable passes through a cavity or a wall that will be lined, the penetration and the conduit should be installed and inspected before the linings close it up. Photograph it. The future installer will not thank you for a route that exists only in your memory, and the owner will not thank you if the installer has to open a wall to find it.

Two details that catch people out:

• The route needs to suit the switchboard location, not just the roof. If the switchboard is on a far wall, the cable run should be planned to that wall from the start.
• The route needs to accommodate both DC cabling from the array and AC cabling from the inverter, which may not follow the same path depending on where the inverter sits.

Inverter location: ventilation, access and noise

The inverter is the part of the system that lives in the occupied building, so its location is a building decision as much as an electrical one. It needs ventilation, because it generates heat and derates when it cannot shed it. It needs to be accessible for maintenance and for reading and isolating. And it needs to be positioned so it does not intrude on the amenity of habitable rooms, particularly bedrooms.

The common failure is the garage wall directly behind a bedroom. It seems convenient at rough-in, the electrician is happy, and then the owner discovers the hum. Moving it later means new cabling, new penetrations and a repair to a finished wall. Nominating the inverter location on the electrical plan and checking it against the room layout on the architectural plan takes minutes at design stage.

Outdoor locations have their own constraints. Direct west sun on an inverter in summer is a real performance problem, so a shaded southern or eastern wall, or a ventilated outdoor enclosure, is usually better than the sunniest wall on the house. Whatever you nominate, confirm it against the manufacturer’s installation instructions for the specific unit — clearances vary and the installer is bound by them.

Switchboard, metering and the electrical rough-in

The switchboard is where solar readiness is most often lost. A board installed with no spare capacity, or positioned where a solar connection cannot be accommodated, forces the installer into a board replacement at the owner’s cost.

At rough-in stage, confirm with the electrician that the board position and size can accept a solar connection, that there is provision for the isolation and protection the installation will need, and that the metering arrangement can be adapted. Where the owner intends to add battery storage later, that intent should be documented now even if the equipment is not specified, because it affects the space and the cable route.

Electrical safety on the DC side deserves specific attention in your site processes. Safe Work Australia’s electrical safety guidance sets out the general duty to manage electrical risk, and the relevant Australian Standard requirements govern how solar installations are designed and installed. The key point for a builder is that DC circuits can remain live when the AC side is isolated, so anyone working near array cabling needs to understand the isolation procedure rather than assume a switch has made the circuit safe. That belongs in the induction for any trade who will be on the roof or in the roof space.

Coordination between trades before the roof is closed

Solar readiness fails most often at the interfaces. The electrician installs the conduit to a switchboard position the plumber then needs to move. The roofer sheets over the nominated array zone without knowing it was nominated. The carpenter frames a valley through the middle of the only usable roof plane.

The fix is unglamorous: put it on the drawings, put it on the electrical plan, and raise it at the pre-start and at every trade coordination meeting until the roof is closed. A single line on the roof plan marking the array zone, and a single line on the electrical plan marking the inverter location and cable route, prevents most of these problems.

The same coordination discipline applies to other services. If the home is getting ducted air conditioning, the roof space is already contested, and our article on ducted air conditioning design and installation covers how to plan that space so the two systems do not fight. For split systems, the outdoor unit and the solar inverter often want the same shaded wall, which is worth resolving on paper rather than on site — see our piece on split system air conditioner installation in NSW for the constraints on that side.

Glazing, thermal performance and the solar ready home

Solar readiness sits inside the broader energy performance of the dwelling, and it is worth being clear with clients about how the pieces relate. Glazing performance is assessed through the Window Energy Rating Scheme, which rates the whole window — frame and glass together — rather than the glass alone. Getting glazing right reduces the cooling and heating load; solar generation then offsets what remains. Neither substitutes for the other.

A client who spends on a large array while accepting poorly performing west glazing has bought generation to cover a load that better glazing would have removed. That is a design conversation to have early, before the window schedule is finalised, because it is the cheapest energy decision on the job.

Worked example: a knockdown rebuild in western Sydney

A builder in western Sydney is putting up a two-storey knockdown rebuild. The roof is a hip with a long ridge running roughly east–west, giving one plane facing the equator and one facing away. The owner has said they want solar but has not engaged an installer.

The builder nominates the equator-facing plane on the roof plan and marks an array zone clear of the ridge, hips and valleys. The plumbing stack is moved to the rear plane during design coordination, which costs nothing at that stage and would have cost a variation later. The roof designer is told an array is intended so the load case is included.

At rough-in, the electrician installs a conduit from the roof space down to a switchboard position on the eastern wall of the garage, with draw wire and caps at both ends. The inverter is nominated on the same eastern wall, which is shaded in the afternoon and does not back onto a bedroom. The switchboard is sized with provision for the future connection.

Before sheeting, the builder photographs the array zone, the conduit entry and the inverter location, and files the images with the electrical plan in the handover pack. When the owner engages an installer after handover, the installer has a nominated zone, a cable route that takes an hour rather than a day, and a switchboard that does not need replacing. The cost of all of that readiness was a handful of design decisions and one conduit.

Documenting readiness for the future installer

Solar readiness only pays off if the information survives to the point of installation, which may be years after handover. Build a simple package: the electrical plan marked with the array zone, inverter location and cable route; photographs of the installed conduit and draw wire; confirmation of the switchboard provision; and any manufacturer documentation for equipment already installed.

Hand that to the owner at handover and explain what it is. It is not a warranty document and it does not commit them to anything, but it turns a future installation from a site investigation into a straightforward job. It also protects you, because it shows the readiness provisions were designed, installed and documented rather than promised.

If you want the design and documentation side of this to be more systematic across your jobs, the guide to how NSW builder CPD works explains how the compliance and technical content fits the annual requirement, and the PointCPD course catalogue lists the sustainability and services units that cover this ground in more depth.

Questions builders ask

• Electrical
• Energy efficiency
• Roofing
• Solar

Published 16 July 2026. General information for builders, not legal, financial or engineering advice for a specific job. Check current requirements with the relevant regulator or standard before relying on them.