4.4 Shading
- General guidelines for all climates
- Fixed shading
- Adjustable shading
- Climate specific responses
- Using plants for shading
- Shading and daylight
- Shading for a healthier environment
Shading of the building and outdoor spaces reduces summer temperatures, improves comfort and saves energy. Direct sun can generate the same heat as a single bar radiator over each square metre of a surface. Shading can block up to 90 percent of this heat.
Shading of glass to reduce unwanted heat gain is critical. Unprotected glass is often the greatest source of unwanted heat gain in a home.
Radiant heat from the sun passes through glass and is absorbed by building elements and furnishings, which then re-radiate it. Re-radiated heat has a different wavelength and cannot pass back out through the glass as easily. In most climates, 'trapping' radiant heat is desirable for winter heating but must be avoided in summer.
Shading of wall and roof surfaces is important to reduce summer heat gain, particularly if they are dark coloured and/or heavyweight.
Shading requirements vary according to climate and house orientation. A general rule of thumb is:
| ORIENTATION | SUGGESTED SHADING TYPE |
|---|---|
| NORTH | fixed or adjustable shading placed horizontally above window |
| EAST & WEST | adjustable vertical screens outside window |
| NE & NW | adjustable shading |
|
SE & SW
|
planting |
GENERAL GUIDELINES FOR ALL CLIMATES
Use external shading devices over openings. Lighter-coloured shading devices reflect more heat. Internal shading will not prevent heat gain unless it is reflective.
Use plants to shade the building, particularly windows, to reduce unwanted glare and heat gain. Evergreen plants are recommended for hot humid and some hot dry climates. For all other climates use deciduous vines or trees to the north, and deciduous or evergreen trees to the east and west.
With ideal north orientation sun can be excluded in summer and admitted in winter using simple horizontal devices, including eaves. For situations where ideal orientation cannot be achieved (eg existing house, challenging site) it is still possible to find effective shading solutions.
[See: 4.5 Passive Solar Heating; 4.3 Orientation]
North facing openings (and south facing ones above the tropic of Capricorn) receive higher angle sun and therefore require narrower overhead shading devices than east or west facing openings. Fixed horizontal shading is often adequate above north facing glazing. Examples include eaves, awnings, and pergolas with louvres set to the correct angle.
East and west facing openings require a different approach, as low morning and afternoon sun from these directions is more difficult to shade. Keep the area of glazing on east and west elevations to a minimum where possible, or use appropriate shading devices. Adjustable shading is the optimum solution for these elevations.
Deep verandahs, balconies or pergolas can be used to shade east and west elevations, but may still admit very low angle summer sun. Use in combination with planting to filter unwanted sun.
Pergolas covered with deciduous vines provide self adjusting seasonal shading. A 500mm gap between the wall and planted screens should be left for ventilation and cooling. Vines on walls (where appropriate) can also provide summer insulation to all orientations. Evergreen vines block winter sun and should only be used in tropical climates.
Use drought tolerant ground-cover plants instead of paving where possible, to keep the temperature of the ground and surrounding surfaces lower in summer.
Protect skylights and roof glazing with external blinds or louvres. This is crucial as roof glazing receives almost twice as much heat as an unprotected west facing window.
Position openable clerestory windows to face north with overhanging eaves to exclude summer sun.
Double glaze clerestory windows and skylights in cooler climates to prevent excessive heat loss.
Advanced glazing solutions such as solar films and tinted glass may be appropriate as a secondary measure on east and west elevations. They can exclude up to 60 percent of the heat compared to plain glass.
Avoid using tinted glass on north facing windows designed to let in winter sun.
[See: 4.10 Glazing]
FIXED SHADING
Fixed shading devices can regulate solar access on northern elevations throughout the year, without requiring any user effort.
Summer sun from the north is at a high angle and is easily excluded by fixed horizontal devices over openings. Winter sun from the north is at a lower angle and will penetrate beneath correctly designed fixed horizontal devices.
Eaves
Correctly designed eaves are generally the simplest and least expensive shading method for northern elevations, and are all that is required on most single storey houses.
The general rule of thumb for calculating eaves width for all latitudes south of and including 27.5S (Brisbane, Geraldton) is given above.
Varying the rule of thumb may be beneficial:
- At high altitudes.
- Where cold winds or ocean currents are prevalent.
- In hot dry inland areas.
- In cold, high latitude areas [eg Tasmania].
For latitudes north of 27.5S the response varies with climate. For high humid climates and hot dry climates with no passive heating requirements, shade the whole building at all times. For hot dry climates with passive heating requirements allow some low angle winter sun to reach walls, concrete floors and especially windows, see Climate-specific responses. [See: 4.5 Passive Solar Heating; 4.6 Passive Cooling][See: 4.5 Passive Solar Heating; 4.6 Passive Cooling]
Permanently shaded glass at the top of the window is a significant source of heat loss, especially in cool and cold climates. To avoid this, distances between the top of glazing and the eave underside should be at least 30 percent of H. See illustration above.
This is not always achievable with standard eave detailing which is flush with the 2100 head. The top 20 percent of this window is in permanent shade.
Above: standard 2100 high doors are shaded by a 1000 eave (including gutter) set 300 above the head. Note the sun angle at midday in mid winter is above the glass line. This configuration provides full shading to glass from late October to late February at latitude 350 (near Canberra) and is appropriate for a higher altitude cool climate winter.
Left: north facing upward raked eaves allow full exposure of glass to winter sun and shade larger areas in summer, without compromising the solar access of neighbours to the south. This inner city terrace in Sydney uses an upward raked eave to passively shade highlight windows. A separate horizontal projection of louvres shades lower glazing. This allows 100 percent winter solar access and excludes all sun between the spring and autumn equinoxes.
Varying the rule of thumb may be beneficial:
- At high altitudes.
- Where cold winds or ocean currents are prevalent.
- In hot dry inland areas.
- In cold, high latitude areas [eg Tasmania].
In colder higher latitudes such as Canberra, Armidale, Coonawarra, Mt Gambier, Albany, Ballarat, Colac, and all of Tasmania.
- Reduce eaves width to 42-43 percent of H to extend the heating season past the equinox.
- Increase window head to eave distance.
In lower latitudes such as Alice Springs, Toowoomba, and Kingaroy, where the need for winter heating is significant but hot summers are common, varying eaves width may not be beneficial.
- Increase window head to eave distance.
Awnings and pergolas
Awnings and pergolas need to extend beyond the width of the north facing opening by the same distance as their outward projection.
For locations north of the Tropic of Capricorn (23.5°S) in hot humid climates or hot dry climates with warm winters, the building and outdoor living spaces should generally be shaded throughout the year.
Louvres
Fixed horizontal louvres set to the noon midwinter sun angle and spaced correctly allow winter heating and summer shading in locations with cooler winters.
Midwinter and midsummer noon sun angles for locations can be calculated using the formulas below, where L is the latitude of your home.
| Midwinter noon sun angle | = | 90 – (L+23.5) |
| Midsummer noon sun angle | = | 90 – (L–23.5) |
| Equinox noon sun angle | = | 90 – L |
The Geoscience Australia website allows you to find the latitude of more than 250,000 place names in Australia, and will calculate the sun angle at any time of the day, on any day of the year.
As a rule of thumb, the spacing (S) between fixed horizontal louvres should be 75% of their width (W).
The louvres should be as thin as possible to avoid blocking out the winter sun.
| ANGLES OF LOUVRES TO THE HORIZONTAL | |
|---|---|
| Hobart | 24° |
| Melbourne | 29° |
| Sydney, Canberra, Adelaide | 31° |
| Perth, Broken Hill, Port Augusta | 34° |
| Brisbane, Geraldton | 38° |