Energy Savings
PROPERTY VALUES
- Homes with higher energy ratings are already fetching premium prices in many areas . This trend is expected to continue if energy costs rise and environmental problems associated with energy consumption manifest.
- Even with advanced glazing and framing systems, glass areas remains the single greatest source of heat loss and heat gain in a home.
- The use of clear glass, particularly on the north elevation, allows maximum winter sun penetration and "free" solar heating. Additionally, the glass significantly reduces the penetration of ultra violet light and reduces fading of furnishings.
- The windows have light transmission in excess of 60 percent, minimising use of artificial lighting and maximizing outlook to the excellent views.
- 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.
- 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.
FIXED SHADING FOR PASSIVE SOLAR ACCESS
- 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.
- 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.
- 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.
- 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.