Why the third planning rule is the one that quietly decides what's possible on inner-city Sydney sites.
Most people who walk into our office with a renovation in mind already know two of the planning controls they'll face. The first is heritage — the listing in the title, the conservation area in the postcode, the streetscape that has to be protected and the front elevation that has to be respected. The second is floor space ratio — the council's number for how much building you're allowed to put on your block.
What they don't know about, almost without exception, is the third rule. The one that doesn't show up in the LEP overview. The one that takes the same project that passed heritage and sat comfortably under FSR and quietly refuses it anyway.
Three hours of sunlight on a winter morning. That's the rule. And on small blocks across the inner west, the inner east and the city, it's the rule that decides more outcomes than most owners ever realise.
What overshadowing actually means
Every building casts a shadow. Council isn't measuring whether yours exists — they're measuring whether yours leaves your neighbour with enough light to live with.
The reference point is 21 June, the winter solstice, when the sun travels its lowest and shortest arc across the northern sky. If your design passes the solar access test on that day, it generally passes year-round. Shadow diagrams are drawn at three intervals — 9am, midday, and 3pm — to show how the shadow moves across that worst-case day.
The rule most NSW councils apply is at least three hours of direct sunlight between 9am and 3pm on 21 June, to at least 50% of the neighbour's principal private open space and to the windows of their habitable rooms.
What counts as habitable matters. A living room is protected. A kitchen is protected. A bathroom or laundry isn't. The room behind the window changes the answer — which is one reason the same shadow can pass on one site and refuse on the next.
Why the inner city is different
Out in the suburbs, blocks are wide and houses sit in the middle. Shadows from one property rarely reach the next one's living room. There's slack in the system.
In the inner west, the inner east, and across the city, there is no slack. Blocks are narrow. Boundaries are close. Houses are built right up to side fences or share party walls. A first-floor addition — even a modest one — can put a long, low winter shadow directly across a neighbour's courtyard or into their north-facing rear window before morning tea.
I sat with the owners of a worker's cottage on a narrow inner west street recently. Two doors down, a neighbour had successfully extended to the rear. Next door, another neighbour had tried for a first-floor addition and been knocked back at pre-DA. Same street. Same heritage controls. Same council. The variable that decided each outcome wasn't the design — it was the way the shadow fell on the property next door at 9am on 21 June.
Heritage you can negotiate. Floor space you can plan around. Shadow is geometry, and geometry doesn't negotiate.
Five things most people get wrong about shadow diagrams
1. Trees don't count. Not at all. The forty-year-old jacaranda casting your neighbour's courtyard into permanent shade is invisible to council. Shadow diagrams are calculated against an empty sky, no matter what's actually growing on the site.
2. Where the shadow falls matters more than how much shadow there is. A small shadow across a living room window can sink a project. A much larger shadow across a side path or a service yard won't. Council is measuring the quality of the impact, not the quantity of it.
3. It gets technical fast. Three specific times of day. One specific day of the year. Specific windows. Specific portions of open space. The whole assessment rides on geometry measured to the minute and to the metre — which is why shadow diagrams sketched from rough plans rarely survive contact with the actual numbers.
4. It's the delta, not the shadow itself. Council isn't asking what shadow you cast. They're asking how much worse it gets compared to what's already there. A substantial development on a site already heavily shaded by tall neighbours or a commercial building behind can sometimes land more easily than a modest one on a sunny block, because the marginal impact is smaller.
5. Shadow rarely refuses a project on its own. It usually becomes the deciding factor when you're already stretching the envelope on floor space ratio, setbacks and overlooking at the same time. If everything else is sitting comfortably within the controls, shadow gets latitude. If everything else is being pushed, shadow is the line council won't cross. The projects that get refused on shadow are almost always the projects that were asking too much in three or four other ways as well.
Why we model it before we design it
For most of my career, the answer to "can we go up?" on an inner-city site was a slow process. Sketch a scheme. Submit a pre-DA. Wait. Read the council's response. Adjust. Resubmit. By the time you knew whether the shadow worked, you had months and several thousand dollars in fees behind you, often with a design you couldn't keep.
That sequence is now backwards. We scan the property first — the building, the boundaries, the neighbours, everything we can see — and build a 3D model accurate to within a few millimetres. Before any design work begins, we can simulate the shadow at 9am, midday and 3pm on 21 June, and watch it fall in real time across the neighbour's roof, courtyard, walls and windows.
On a recent project in the East, we ran five massing options in a single afternoon and showed the client, standing in their own kitchen, why a one-metre setback at the rear changed a refused application into an approved one. On another in the inner west, the same exercise told the owners — early, before they'd committed any further fees — that a second storey wasn't going to land on their block. They saved themselves months and walked away with a clear-eyed plan for what was actually achievable.
That's not a sales pitch for the technology. It's a practical answer to a problem that used to swallow projects whole.
What it means for your project
If you're looking at a heritage cottage, a tight terrace, a corner block on a narrow street — anywhere in the inner west, the inner east, the lower north shore, or the city — heritage and FSR will be the rules everyone tells you about. The shadow rule is the one nobody mentions until it has already cost you.
The good news is it's a question with a definitive answer. It just needs to be asked early, and asked properly, with the right tools.
Our fixed-fee design consultation includes a 3D scan of your property, a shadow study against your specific planning controls, and two design options tested against them. You'll know what's possible — and what isn't — before you spend anything else.
