Siting and solar access

ShadowsHow long they really are in winter

On the shortest day, Canberra's sun is 31° above the horizon at noon and about 17° at 9 am and 3 pm (solar time). Shadows are long:

At noon a shadow is about 1.6 times the height of whatever casts it. Three hours either side, it's more than three times. A two-storey house next door can shade most of a suburban backyard for much of a winter's day. An ordinary fence can put the bottom of a living-room window in shadow if the window sits close to it.

The winter sun spends the day in the northern sky, so what matters is mainly what lies to the north-east, north and north-west of your windows. A building or tree to the south doesn't matter in winter.

The ACT rulesSolar envelope, solar fence and the three-hour test

The Territory Plan protects a minimum of winter sun for every residential block. The ACT's technical specifications set three main controls for single houses:

• The solar envelope. A house must fit under an imaginary sloping plane. The plane starts at a "solar fence" on the boundary with the neighbour to its south, and rises northward at 31°. That angle is the height of the midwinter noon sun, so the plane traces the edge of the shadow a building would cast at noon on the shortest day.
• The solar fence height depends on block size. On large blocks it is 2.4 m along the main building zone and 1.8 m elsewhere. On mid-sized and compact blocks it is 3 m and 2.3 m.
• The three-hour test. A new house must leave its neighbour at least three hours of direct sun between 9 am and 3 pm on 21 June. That sun must reach a daytime living space, or at least half of the neighbour's minimum private open space. Existing solar panels and solar hot water on a neighbouring roof must keep at least four hours.

The rules cut both ways. They limit how high you can build near your southern boundary, and they limit what your northern neighbour can build near yours.

The NSW rulesCouncil by council

In NSW, solar access for houses is set mostly by each council's development control plan, so the details vary. A typical set of controls, from one Sydney-fringe council:

• At least one living area of the new house must get three hours of direct sun between 9 am and 3 pm on 21 June.
• At least half of the private open space, both on the site and on the neighbouring properties, must get the same three hours.
• At least one living-area window of each neighbouring house must keep three hours of sun.

Councils usually allow exceptions where the neighbour's living areas are badly placed, or where topography, existing buildings or trees already block the sun. Check the actual development control plan for your council.

SitingWhere the house goes on the block

The ACT envelope rises at the midwinter noon sun angle, so it tells you how far back from the northern boundary your own windows need to be. On the main building zone of a large block, with a 2.4 m solar fence, a window set at least 4 m from the northern boundary keeps its midwinter noon sun all the way to the floor, however much the northern neighbour builds within the rules. On a compact block, with a 3 m solar fence, that distance is about 5 m. Closer than that, the bottom of the window may be in shadow at noon. Morning and afternoon shadows are longer again.

That setback is more than a rule. It becomes the north garden:

• Put the garden and outdoor living on the north side of the house, between the house and the northern boundary. A garden south of a house sits in the house's own shadow all winter. A single-storey house shades about 5 m behind it at midwinter noon.
• Keep tall planting and outbuildings out of the north garden, or choose deciduous species and set them well back.
• Use the south side for the driveway, garage and services. It gets no direct sun in winter.
• On sloping blocks, a fall to the north helps and a rise to the north hurts. Stepping the floor levels or raising the living level can recover sun that a flat plan would lose.

Before you buyWhat to check on a block

Solar access is decided largely by the block you choose. Look for these before you buy:

1. Where is north? Check it with a phone compass set to true north, not by guessing from the street.
2. What's to the north? Note the neighbouring houses, their height and distance, and any big evergreen trees. A two-storey house 8 m beyond your boundary can still shade the northern part of your block for much of a winter's day.
3. What could be built to the north? An empty block or an old single-storey house can become a two-storey home under the rules. Look at what the planning envelope allows, not just at what's there now.
4. Which way does it slope? A fall to the north is an advantage. A steep rise to the north is a real cost.
5. Are there protected trees? In the ACT, regulated trees on your block or the neighbour's may be hard to remove or prune.
6. Is the block wide enough on its north side for living areas and a garden to share the sun?

Visiting the block on a winter afternoon will tell you more than any plan.