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Drought Tolerant, Feature Trees, Garden Design, Shade

Shade Trees That Cut Cooling Bills: Placing Trees to Shade a House

Chinese pistachio (Pistacia chinensis), a deciduous shade tree that shades a west facing wall in summer and lets the low winter sun through once bare.

Nursery Near Me |

A house that runs hot in summer is almost always a house with sun on its glass and its western wall. The one idea that matters most is to stop that sun before it reaches the building. Shade cast outside the window and across the wall does more than any blind hung inside, and a well placed tree is the cheapest way to cast it.

This guide gathers what the Australian Government's Your Home guide, the national energy.gov.au advice, city urban forest strategies and university tree research say about shading a home with trees, and adds the horticulture on which trees do it without damaging the house. It summarises their advice and is not a substitute for it; the sources are linked at the end.

Quick facts

First principle Shade the outside of the glass and the west wall. An internal blind stops the sun after it is already in
North side Winter sun in, summer sun out: eaves first, then a deciduous tree, or one set back so low winter sun passes under the canopy
West side The harshest afternoon sun. Dense evergreen or tall deciduous shade, the closest tree to the house you will plant
South side No shading needed south of the Tropic of Capricorn. In the tropics every side needs it
Distance At least half the mature spread from walls, no limbs over the roof, and large trees their mature height from footings on reactive clay
Timing Plant in autumn or spring, never midsummer. Fast species shade a window within three to five summers

Why shade outside the glass

The Your Home guide explains the mechanism. Sunlight passes through glass and is absorbed by floors, walls and furniture, which re-radiate it as longer wavelength heat that cannot pass back out as easily. Your Home says unprotected glass is often the greatest source of heat entering a home, that shading it is the best way to reduce unwanted heat gain, and that effective shading can block up to 90 per cent of the heat direct sun lands on a surface.

An internal blind cannot do that. It stops the light after it has crossed the glass, and the blind itself warms and radiates into the room. Eaves, awnings, screens and trees stop the sun before the glass. Walls count too: Your Home notes that shading dark or uninsulated walls reduces the heat load, and energy.gov.au lists external shading or deciduous trees among the simple steps that cut cooling loads and says shading around the home improves the efficiency of the air conditioner itself.

Which side of the house matters

In the southern hemisphere the sun tracks through the northern sky. Your Home works in solar north, which can differ noticeably from a compass; a phone map set to true north is close enough.

  • North. Winter sun arrives low and is wanted; summer sun arrives high and is not. Eaves handle most of it, and Your Home's rule for all but the hottest climates is that planting to the north should be deciduous, or set back with a clean trunk so low winter sun passes under the canopy. In cool climates Your Home advises against anything to the north that obstructs winter sun; even bare branches cast some shade.
  • West. Afternoon sun strikes low, for hours, on walls already warm. Your Home calls west facing glass and walls a significant source of heat gain in hotter climates and notes that low sun is hard to block with fixed structures. A tree's shade is tall and vertical, so the largest tree the space allows belongs here.
  • East. Milder, but Your Home says morning gain starts a cumulative process felt by late afternoon. Shade it in hot climates; in cool ones it is a lower priority.
  • South. South of the Tropic of Capricorn a south wall needs no shading. North of it the midsummer sun sits in the southern sky, so in Darwin, Cairns and Broome Your Home says to shade every side.

Because afternoon sun is low, a tree set back by half its mature spread still throws its shadow across the west wall from mid afternoon, when it is needed.

Deciduous or evergreen: the climate decides

Your Home's guidance is short: evergreen shade for hot humid and some hot dry climates; elsewhere deciduous to the north and either type east and west; in cool temperate climates deciduous east and west with the north kept open. By region:

  • Tropical and subtropical north (Darwin to Brisbane, northern Western Australia). Shade is welcome all year, so evergreen on every side, placed without blocking cooling breezes.
  • Warm temperate coast (Sydney, Newcastle, the Perth coast). Deciduous to the north for winter warmth, either type on the west.
  • Cool temperate south (Melbourne, Canberra, Hobart, the tablelands). Winter sun is worth more than summer shade: deciduous west and east, nothing tall to the north.
  • Perth and Adelaide (hot dry summers, mild wet winters). Deciduous trees on the west and north are the classic answer, from species that shrug off a dry summer.
  • Dry inland. Drought tolerance decides. Evergreen natives from the dry country give reliable shade; deciduous trees suit the north where winters are cold, but need water to establish.

One catch: some warm climate trees sold as deciduous are bare in late winter and spring rather than through the cold months, so they give summer shade without the winter sun. The list below says which.

Distance, roots, pipes and powerlines

Mature size is the number that matters, not the size in the pot. Our canopy tree guide gives spreads for the common choices.

  • Walls and roof. Set the trunk back at least half the mature spread, so the canopy reaches the wall without limbs over the roof, where they fill gutters and carry embers.
  • Footings. On reactive clay, which underlies much of Melbourne, Adelaide, western Sydney and the inland, roots dry the soil and footings move. CSIRO's homeowner guide on foundation maintenance and the footing standard AS 2870 treat this as a real risk; the usual rule of thumb is a single large tree no closer than its mature height, further for rows.
  • Pipes. Roots follow moisture to leaking joints. Keep vigorous species off the sewer line; our guide to planting near pipes lists the well behaved ones, and Your Home says the same in one line: avoid destructive roots close to the house.
  • Powerlines and panels. Distributors such as Energex, Ausgrid, Essential Energy, SA Power Networks and Western Power publish lists of species safe under wires and prune anything that reaches them, so a shade tree under the lines becomes a shape you did not choose. Put the big tree elsewhere, and never where it will grow to shade a solar array, yours or the neighbour's.
  • The air conditioner. The outdoor unit sheds heat into the air around it and works harder when that air is hot; a unit on paving against a west wall sits in the hottest air on the block. Shade over it helps, provided the installer's airflow clearances are kept and nothing drops leaves into the fins. A small deciduous tree or the edge of a larger canopy is right; a hedge hard against the unit is not.
  • Paving. Your Home advises planting instead of paving to reduce ground temperature and reflected heat, because gardens and soil cool the air passing over them by evapotranspiration. Shade the driveway and the western paving, or replace paving with plants.

Street trees and council rules

The tree on the verge belongs to the council: planting, pruning or removing it needs permission, and many councils will plant one on request. Cities want canopy for the same reason you do. The City of Melbourne's urban forest strategy aims to lift canopy cover from 22 to 40 per cent by 2040 to bring inner city temperatures down, and the City of Sydney targets 27 per cent by 2050 from 15.5 per cent in 2008. Most councils protect established trees above a set size, so check before removing one. For species choice at estate scale, Which Plant Where, built by Macquarie University with Hort Innovation and Western Sydney University, rates species for survival under future climates.

Trees that do the job

Sizes are typical in gardens. All are in our feature trees collection, the natives also in Australian natives.

Deciduous trees for winter sun and summer shade

Evergreen trees for shade all year

What to keep away

  • Camphor laurel (Cinnamomum camphora). Enormous, with roots that lift slabs and enter pipes, and an environmental weed across Queensland and New South Wales.
  • Chinese tallow (Triadica sebifera). Good autumn colour, and a serious invasive weed in Queensland and New South Wales, spread by birds.
  • Large gums against walls. Spotted gum, flooded gum and their kind are fine trees 20 metres from a house and the wrong trees at 5, for limb drop, size and roots.
  • Figs, willows, poplars and liquidambar. Roots that crack pipes and lift paving; most willows are Weeds of National Significance.
  • Wrong placements. An evergreen to the north in a cool climate; any tree under powerlines; limbs over the roof; anything vigorous over a sewer line; a hedge against the air conditioner; a tree that will one day shade a solar array.

Getting it right

  • Watch the shadows first. Your Home recommends sun path apps, which overlay the sun's track on your phone camera, for judging the shade a tree will cast. Check midwinter noon before planting north of a window.
  • Plant in the mild seasons. Autumn in the south and in Perth and Adelaide, spring after the frosts inland, the start of the wet season in the tropics. Our planting time guide has the detail by region.
  • Buy the biggest tree you can water. Advanced stock shortens the wait but needs deep watering through two summers. Fast species such as crepe myrtle, jacaranda, white cedar and tuckeroo shade a window within three to five summers; bottle trees and magnolias take longer.
  • Mulch wide, water deep. Keep mulch off the trunk and water deeply and less often, to send roots down rather than along the footings.
  • Lift the canopy. Remove lower limbs gradually so winter sun passes beneath the crown. Never top a tree; the regrowth is weak. Your Home's advice to prune vegetation that blocks winter sun applies every year.

A word of caution

This page is general guidance. Footings on reactive clay, a tree near a sewer main or under powerlines, and any street or protected tree are governed by specific rules: ask a structural engineer, the electricity distributor, the council, and a consulting arborist about any established tree near a house. Shade helps every home; it does not replace insulation, sealing and sensible glazing.

Sources

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