Shading Windows to Keep a Home Cooler

Glass lets light into a home, but it also lets in heat. On a hot afternoon a bare window can turn a pleasant room into one you avoid. Good shading fixes much of that before you ever reach for the air conditioner.

Shading is also a design decision, not just a practical one. Eaves, awnings, pergolas and screens shape how a house looks from the street and how the rooms feel inside. Getting them right early saves money and adds character.

Why windows need shading

Unprotected glass is often the biggest source of heat entering a home. The Australian Government’s Your Home guide to shading says direct sun can deliver as much heat per square metre as a single bar radiator. It also says good shading can block up to 90% of that heat. That is a large gain from something as simple as an overhang.

Shading walls helps as well. Uninsulated walls and dark walls soak up heat and pass it inside. If you are choosing a facade finish, think about how much sun it will take, as the choice between smooth or rough stone cladding is only part of the picture. Shade over that wall matters too.

Roof glass is the hardest to manage. Your Home notes that roof glazing receives almost twice as much heat as an unprotected west window of the same size. Skylights should be kept modest in size and protected with external blinds or louvres. A small skylight still brings in plenty of light.

Getting the eaves right on north windows

North facing windows are the easiest to shade well. In summer the midday sun sits high, so a fixed eave can block it. In winter the sun sits lower and slips under the same eave to warm the room. That simple geometry is the basis of passive design.

For most of southern Australia, Your Home gives a rule of thumb. Make the eave width about 45% of the height from the window sill to the underside of the eave. This fully shades the glass for roughly a month either side of the summer solstice. It still lets full sun in for about a month either side of the winter solstice.

A few other details make the eave work better. Leave a gap between the top of the glass and the eave of at least 30% of the window height. Let horizontal shades run past each side of the window by the same distance they project. In warmer areas round the eave width up, and in cooler areas round it down.

East and west windows need a different approach

Morning and afternoon sun comes in low. An eave does very little against it. That is why Your Home suggests keeping east and west glass to a minimum where you can. West facing glass and walls are a big source of heat in hotter climates.

Vertical shading works best on these sides. Think louvres, fins, sliding screens or a lattice covered in a climbing plant. Deep verandas also help, though very low sun can still reach under them. Your Home rates adjustable external blinds as the best option for east and west windows.

Afternoon sun can also be tough on what sits inside the window. Fabrics near west glass take the full force of that light day after day. Shading the glass outside is a simple part of caring for upholstered furniture in a sunny living room. Internal curtains help with privacy, but the heat has already come through the glass by then.

Adjustable shading for changing seasons

Fixed shading cannot respond to a cool spring day or a hot autumn one. Adjustable shading can. Your Home lists sliding screens, louvre screens, shutters, retractable awnings, external blinds and removable shade cloth over pergolas. Shade cloth is flexible and low in cost.

North east and north west windows benefit most from adjustable systems. They can block all summer sun and let in full winter sun. They can also be set somewhere in between on mild days. Your Home also points out that adjustable shading helps a home cope as the climate changes.

Design wise, these options give a house a lot of personality. Timber shutters suit a coastal or heritage style. Slim aluminium louvres suit a modern facade. Fabric awnings can add colour to a plain brick front.

Using plants and pergolas as shade

Plants are one of the most attractive ways to shade a home. A deciduous vine on a north pergola gives leafy shade in summer. In winter the leaves drop and the sun comes through. Your Home suggests evergreen plants in hot humid climates and some hot dry ones.

Different plants suit different jobs. Tall trees can shade a roof, while shrubs are better for shading windows. Vines on walls cut summer heat and reflected heat. Your Home recommends native species that need little water.

This is where house design meets the garden. Many of the small courtyard and balcony garden ideas that suit Perth homes also cool the rooms beside them. Check local council rules before building a pergola or verandah, as approvals vary by area. The rules and regulations before you start landscaping are worth reading first.

Matching shading to your climate

Australia has very different climates, so one shading plan does not suit every house. Your Home gives broad advice for each climate type. In hot humid areas, shade walls all year and shade every opening, including south facing ones. A fly roof can also help.

In hot dry areas, shade all openings if the home needs no winter heating. Where winter heating is needed, keep north glass in the sun during the cooler months. In warm and mild temperate areas, shade north openings and use adjustable screens or deep overhangs on the east and west.

Cool temperate areas are different again. There the aim is to keep north glass fully exposed to winter sun. Deciduous planting on the east and west is recommended. Deep balconies on the north side are best avoided, as they block the winter sun you want.

Frequently asked questions

Are internal blinds enough to keep a room cool?

Internal blinds help with glare and privacy. The sun has already passed through the glass by the time it reaches them, though. External shading stops the heat before it gets inside. For hot east and west windows, outside shading is the better choice.

How wide should my eaves be?

For north windows in most of southern Australia, Your Home suggests about 45% of the height from the sill to the underside of the eave. Round up in warmer areas and down in cooler ones. Different rules apply in the far north of the country. A building designer can check the numbers for your site.

Can trees do the job instead of awnings?

Trees and vines can provide very good shade. Deciduous plants on the north let winter sun through once their leaves fall. On the east and west, deciduous or evergreen trees both work. They take time to grow, so many homes use plants and built shading together.

What about skylights?

Skylights take in a lot of heat for their size. Keep them small and fit external blinds or louvres where you can. A modest skylight still lights a room well. Openable clerestory windows facing north under an eave are another way to bring in light.