Passive solar design: orientation, eaves, glazing and thermal mass that actually work

Every house either works with its climate or against it. A home that faces the right way, shades its windows in summer, lets the winter sun in, and holds its temperature can be comfortable for much of the year with little heating or cooling. A home that ignores those principles relies on air conditioners and heaters to make up the difference, every day, for decades.

Passive design is not new or exotic. It is the set of basic principles that good designers and builders have used for generations, and it is the cheapest way to make a house energy efficient because most of it costs little or nothing extra when done at design stage. It also makes energy ratings easier to meet, whether through NatHERS or BASIX in NSW.

The core principles

Orientation

In the southern hemisphere, the sun is to the north. In most of southern and temperate Australia, putting living areas and most of the glazing on the north side lets the house collect winter sun when it is wanted and control summer sun with simple shading. Bedrooms, bathrooms, laundries and garages can go on the south, east or west, where their glazing needs are smaller.

Builders often do not choose the orientation; the lot and the design do. But on estates where builders offer a range of designs, choosing and flipping designs to suit each lot’s orientation is one of the most effective things a builder can do for the home’s performance.

Shading

The sun is high in summer and low in winter. Eaves on north-facing windows, sized for the latitude, block the high summer sun and let low winter sun in. East and west windows receive low-angle sun in the morning and afternoon, which eaves cannot block, so they need external shading such as pergolas, louvres or blinds, lower solar gain glass, or simply smaller windows.

Glazing

Glass is the weakest part of the thermal envelope. The right amount of glazing, in the right places, with the right performance for each elevation, is central to passive design. Too much unshaded west-facing glass is the most common cause of overheating in Australian homes.

Thermal mass

Heavy materials such as concrete, masonry and tiled slabs absorb heat and release it slowly. Used well, thermal mass evens out temperature swings: it soaks up winter sun during the day and releases it in the evening, and in summer it absorbs heat and can be cooled at night with ventilation. Used badly, it becomes a heat store in summer or a cold sink in winter. Mass works best inside the insulated envelope, exposed to winter sun, shaded in summer, and in climates with a significant difference between day and night temperatures.

Insulation and sealing

Insulation and air sealing hold the heat in or keep it out. Passive solar gain is wasted if the house loses it through uninsulated walls or leaky downlights. A complete, continuous insulated and sealed envelope is the foundation that makes the other principles work.

Ventilation

Cross-ventilation, with openable windows on opposite sides of rooms and the house positioned to catch prevailing breezes, is the cheapest cooling there is. Stack ventilation, using high windows or vents to let hot air escape, helps purge heat on summer evenings.

Climate matters

Australia’s climates range from tropical to alpine, and passive design priorities change with them.

Most NSW housing is in temperate climates, where the aim is to balance winter heating and summer cooling. The classic strategies, north orientation, sized eaves, controlled east and west glazing, some thermal mass and good cross-ventilation, suit most of the state’s coastal and inland population centres.

Passive design and energy ratings

Energy assessment tools model the heating and cooling a home needs based on its design and construction. A home designed with passive principles needs less heating and cooling, so it achieves a better rating with less expensive upgrades. A home that ignores them may need costly high-performance windows, extra insulation or other measures to reach the same rating.

That is why passive design is also a cost strategy. In NSW, where BASIX requires thermal performance broadly equivalent to 7 NatHERS stars for most new homes, a well-oriented, well-shaded design can meet the target far more cheaply than a poorly oriented one.

What builders can do

Much of passive design is decided by the designer, but builders influence it in three ways: at design stage, through the choices they offer; during construction, by building what was designed; and at handover, by helping clients use the house well.

A worked example: flipping the plan

A builder is offering a standard four-bedroom design on two lots in the same street. On one lot, the rear faces north; on the other, the front faces north. The standard plan has the living areas at the back.

On the first lot, the living areas face north as intended. On the second, a straight copy would put the living areas and their large glazed doors facing south, with the bedrooms taking the northern sun. The builder offers a flipped or reversed version with living at the front, adjusts window sizes and eaves, and the energy assessment for the second lot improves significantly with no extra cost for high-performance glass. Both clients get a comfortable house.

Small lots and medium density

On narrow suburban lots and in townhouses, perfect orientation is often impossible. Passive principles still apply, adapted to the constraints. Where the living areas cannot face north, clerestory windows or skylights can bring in winter sun from above. Courtyards can bring light and air into the middle of a deep plan. Party walls between townhouses provide thermal mass and reduce exposed wall area. Cross-ventilation can be achieved through careful placement of openings and internal doors. Good medium-density design uses these techniques to perform well on sites that would defeat a standard house plan.

Roof and colour

The roof receives more sun than any other surface. Roof colour, roof space ventilation and ceiling insulation all affect summer heat gain. Lighter-coloured roofs reflect more sun and keep roof spaces cooler, which is especially valuable in hot climates, and the roof colour is an input to energy assessments. A client who changes to a dark roof late in the build may be changing the energy rating too.

Landscaping

Landscaping is part of passive design. Deciduous trees on the north and west shade the house in summer and let sun through in winter once their leaves drop. Evergreen planting on the west and south-west can block hot afternoon sun and winter winds. Paved areas close to the house absorb and re-radiate heat in summer. Builders who hand over with landscaping advice help clients get more from the design.

Helping clients use a passive house

Passive design works best when occupants understand it: opening windows on summer evenings to purge heat, closing them in the morning, drawing blinds on east and west windows, letting winter sun reach the floor rather than covering it with rugs, and using ceiling fans before air conditioning. A short explanation at handover, in plain language, helps clients get the benefit they paid for.

Checking the design before you price it

When pricing a client’s design, a quick passive design check can save both parties money: which way do the living areas face, how much unshaded west glass is there, are the eaves sized sensibly, and will the energy assessment need expensive upgrades? Raising those questions before the contract gives the client a chance to adjust.

Passive design and the budget

Clients sometimes assume energy efficiency means expensive add-ons. The passive principles are mostly about arrangement, not extra cost: which way the living room faces, how big the eaves are, where the windows go. Getting them right early often saves money, because the energy target can be met without premium glazing or oversized air conditioning.

Retrofitting existing homes

Existing homes cannot be reoriented, but many passive improvements are possible: adding external shading to west windows, planting deciduous trees, adding eaves or pergolas, improving insulation and sealing, upgrading windows on the worst elevations, and improving cross-ventilation. Renovation builders who understand passive principles can offer clients improvements that make a real difference to comfort.

The bottom line

Passive design is the most cost-effective energy efficiency there is. Face living areas north where possible, shade for summer and admit winter sun, control east and west glass, use thermal mass where it suits the climate, insulate and seal thoroughly, and design for ventilation. Builders protect it by building exactly what was designed and resisting substitutions and savings that quietly undo it.

Questions builders ask

• BASIX
• Energy efficiency
• Passive design
• Windows and glazing

Published 28 August 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.