Renovating or extending? Planning solar while the builders are on site avoids costly rework. We cover roof layout, conduits, switchboard space, extending versus a second system, and timing with your builder. The best time to plan solar for an extension or renovation is at the design stage, long before the panels go up. Panels are installed once the new roof is finished, but the decisions that make that installation simple, such as roof layout, cable routes and switchboard space, are locked in much earlier. A short conversation with us while the plans are still on paper can save the cost of opening walls, moving vents or replacing a switchboard twice.
Plan the roof before it is framed
A renovation is a rare chance to shape the roof around solar instead of working around whatever is already there. When you review plans with your architect or builder, keep these points in mind.
- Orientation. North-facing roof planes typically give the highest yearly production in Sydney. East and west planes also work well, spreading production across the day, and suit households that use more power in the morning or late afternoon.
- Clear space. Whirlybirds, exhaust vents, flues, skylights and antennas placed on the best roof face can remove several panels from the layout. Ask whether they can sit on a south-facing plane instead.
- New shade. A second storey or a raised roofline can shade panels on a lower roof, sometimes for months of the year when the winter sun is low. Existing panels may need to move.
- Roof material and structure. Tile and metal roofs need different mounting, and some designs call for a structural check of the framing.
Rooftop solar on a house is often permitted without a separate development application in NSW, but heritage items, conservation areas and some designs can change that, so raise it with your builder or certifier early. Our roof suitability checker is a quick way to test a roof plane before the plans are finalised.
Wiring and switchboard work while the walls are open
Once plasterboard is up, every new cable route costs more. During the rough-in stage, ask your electrician to allow for the following:
- a conduit from the roof space down to the planned inverter location;
- a data cable or reliable Wi-Fi coverage at the inverter for monitoring;
- wall space for a battery, preferably shaded and out of the weather, even if the battery comes later;
- a dedicated circuit, or at least a conduit, to where an EV charger could go;
- spare room in the switchboard for solar, battery and EV protection devices.
Renovations often trigger a switchboard upgrade anyway, particularly in older Sydney homes with ceramic fuses or a crowded board. If that is happening, make sure the new board is sized for your energy plans rather than only today's circuits. All of this work must be carried out by a licensed electrician.
Renovating to go all-electric
Many renovations now replace gas appliances at the same time. Swapping a gas cooktop for induction, gas hot water for a heat pump or gas heating for reverse-cycle air-conditioning moves that energy onto your electricity bill, which changes how much solar makes sense. It also changes the load on your supply: an induction cooktop, heat pump, ducted air-conditioning and EV charger together can push an older switchboard or consumer mains past their limits.
That is why the order of upgrades matters. A heat pump set to run during solar hours can absorb daytime generation that would otherwise be exported for a few cents, so it pairs naturally with a larger array. Our market lists an Induction and Electrification Assessment for $199 per home (fee credited), which checks switchboard and supply capacity and sets out a sensible sequence of upgrades. Size the solar for the house you are building, not the house you are leaving.
Extend the existing system or add a second one?
If you already have solar, the extension raises a common question: add panels to what you have, or install a separate system on the new roof? The answer depends mostly on the existing inverter.
| Consideration | Extend existing system | Separate second system |
|---|---|---|
| Inverter capacity | Only works if the inverter has spare capacity | New inverter sized for the new array |
| Panel matching | Older panel models are rarely still available | New panels on their own circuit |
| Roof layout | Best when new panels face the same way | Handles a different orientation easily |
| Monitoring | One app | Possibly two apps, unless the equipment allows combined monitoring |
| Battery readiness | Depends on the existing inverter | A hybrid inverter can make a future battery simpler |
Either way, the added capacity needs network approval, and the total on the property must fit within your export arrangements. STCs can apply to eligible new capacity, and their value steps down each 1 January, which is worth knowing if your renovation runs across the new year. Our STC rebate guide explains how the discount works. If the existing inverter is ageing, replacing it with a hybrid inverter that runs both old and new panels can be the tidiest result.
Timing solar with your builder
Solar installers and builders work best when the sequence is agreed early. A typical order looks like this:
- Design stage: we review the plans, roof faces and switchboard, and suggest a panel layout.
- Rough-in: conduits, battery wall space and switchboard capacity are allowed for before walls are lined.
- Network application: lodged once the design is settled, so approval is not the item holding up switch-on.
- Roof completion: panels go on after the roofer finishes, never on a partly completed roof.
- Installation and commissioning, ideally while scaffolding or edge protection is still in place.
- Meter changes and final handover once the electrical work is signed off.
Scaffolding is worth a mention. Roof work requires proper fall protection, so if the builder's scaffolding can stay up a few extra days for the solar installation, ask about it. It can simplify access for our team. If your existing panels must come off for re-roofing, the removal and reinstallation needs to be done by an accredited installer and electrician.
Next steps
For reference, our published indicative prices for Sydney in 2026, after STCs, are $4,500-$6,500 for a 6.6 kW system and $7,000-$9,500 for a 10 kW system. For existing owners, Solar System Upgrade and Additional Panels is listed in our energy market from $2,990 per upgrade. All prices are indicative and confirmed after a site assessment. Send us your plans and request a quote while the design is still flexible, and our team will work with your builder's timeline.
Frequently asked questions
Should I wait until the renovation is finished before asking for a solar quote?
No. Talk to us while the plans are still being drawn, because that is when conduits, switchboard space and roof layout can be adjusted at little or no cost. We can prepare a design and indicative price from the plans, then confirm the final layout on site once the roof is built. Waiting until the builder leaves often means extra cable runs, patching or a second switchboard upgrade.
Can my existing panels go back on after re-roofing?
Often they can, if the panels and mounting are in good condition and still suit the new roof. That said, reinstallation costs money, older panels produce less per square metre than current ones, and the inverter may be nearing the end of its life. We compare reinstating the old system with replacing it, so you can decide with both costs in front of you rather than defaulting to either.
Can solar panels go on the flat roof of a new extension?
Yes, in most cases. Flat and low-pitch roofs usually need tilt frames so the panels shed water and dirt and face the sun at a better angle, and every roof penetration must be sealed properly to protect the membrane. Tell your builder early so the structure and waterproofing allow for it. Our market lists Waterproofing for Solar Installation from $390 per roof, and any tilt frames appear as a separate line on your quote.
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