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Passive solar design

Passive solar design means heating, lighting and cooling your home using the sun’s heat and light. This will slash your energy use, reducing energy bills and greenhouse gas emissions, while making your home more comfortable.  This article explains the basic principles of passive solar design. But each home and block of land is unique, so consider using an architect or building designer to help you design a home that works on your block.

The key principles of passive solar design are orientation, insulation, shading and air flow. The basic aim is to exclude sunlight during summer, so your home stays cool, but allow it in to warm your home in winter.  Before planning your home, spend time on your block. Identify where the sun will be throughout the year, and where the predominant local breeze comes from. Look for nearby shade features that affect your land, such as tall trees.

Some principles of passive solar design;

Orientation

The direction your home faces is the starting point of passive solar design. Living areas should face north so winter sunlight can enter through north-facing windows. If possible, avoid east and particularly west-facing windows. They are harder to shade in summer because they get the lower morning and afternoon sun.

Put bedrooms on the south side. They don’t need heating or cooling in the day anyway, and in hot, humid regions south-facing windows won’t heat up so much. And put bathrooms, utility rooms and garages on the west or east to help insulate living areas.
North = living areas
South = bedrooms
East/west = laundry/utility/garage/bathroom
Sometimes getting the best orientation and positioning on your block means thinking outside the box – switching bedrooms to the front of the house, for instance, or building at the back of the block instead of the front.

Insulation

Unless your home has adequate insulation, you’re fighting a losing battle. Heat will simply get in or out through the walls, roof and windows. Wall and roof insulation are essentials and in more extreme climates you could consider double-glazing windows. Make sure windows seal and fit draught-excluders to doors and windows.  If you are building, eco-friendly building materials such as rammed earth or mudbrick have excellent insulating properties.

Shading

Curtains, awnings, shutters and blinds allow you to adjust the amount of heat entering or escaping from your home through your windows. In summer, you can stop your home heating up by shading windows, then at night open them up to let the house cool down. In winter, let sunlight in during the day then draw curtains at night to keep heat inside.  Eyebrow awnings and eaves above north-facing windows provide shade when the sun is high in summer but let in sunlight in winter when the sun is lower. West-facing windows, however, need full-length blinds or curtains to shield out the lower afternoon sun.

Shading is more effective if you stop the heat before it hits the window – that means external shading such as an awning to exclude heat in summer, and internal shading such as curtains to retain heat in winter.  Another way to shade windows is to plant deciduous bushes in front of them. The bushes will provide shade in summer then shed their leaves to let in sunlight in winter.  Similarly, tall trees with high canopies can shade your roof in summer while still letting in winter sunlight, and climbing vines can help keep sun-exposed walls cool.

Air-flow

Try to identify the direction of the predominant breezes to your block when building. Place doors and windows on different sides of rooms where, when opened, they will allow a cooling breeze to blow through your home. In the humid tropics, try to ensure bedrooms can get some air-flow on hot nights. Ceiling and portable fans also help circulate air.

Other passive design tips include;

Skylights

Skylights can let in three times more light than vertical windows. They are a great way to let light into rooms with less heat loss or gain than normal windows. Double-glaze skylights and fit them with blinds to minimise heat loss and gain.

Thermal mass

Dense materials take longer to warm up but retain heat for longer. So a concrete slab floor will absorb heat in the day and release it slowly at night – helping to provide warmth on winter nights in cooler zones. In hot regions, on the other hand, more lightweight flooring will cool down faster in the evening.

Colour

If you live in a warm climate, lighter-coloured tiles and bricks will reflect heat, helping keep your home cool. (And, conversely, in cool climates, dark colours absorb heat.)

Internal doors

Open-plan home have become popular in recent years but it’s worth retaining, or adding, internal doors. You can leave them open to let breezes circulate, but you can shut them on hot or cold days so you only cool or heat the room you are in, not the whole house.

Outdoor living spaces

Link outdoor spaces such as courtyards, patios and verandahs with internal living areas to provide sunny spots in winter and cool shaded areas in summer.

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