When it comes to maintaining a comfortable temperature inside your home, it pays to think about how the sun hits your windows. Windows are one of the most significant elements in your home’s heat gain and loss.
One of the simplest, most cost-effective and efficient ways to protect your home from the heat is by properly shading your windows. For those living in the southern hemisphere (ie. Australia), its particularly important to use efficient and simple fixed horizontal shading on northern elevations to properly shade windows, especially during the summer months. On non-northern elevations it is best if shading is vertical.
What are Eaves?
Eaves are the extension of the roof over the side of the house. These can play a crucial role in regulating the amount of sunlight admitted into your home at different times of the year. If eaves are correctly designed, they will block summer sun (which sits higher in the sky) while still admitting winter sun (which sits lower in the sky).
For example, a 600mm eave is similarly successful in blocking out mid-summer sun to the 1200mm eave but casts far less shade in mid-winter. In variable climates such as Melbourne some days in spring and autumn can be just as hot as those days in mid-summer. At these times, the 600mm eave alone may not be sufficient and additional adjustable shade may be needed.
In Brisbane, however, the need for summer cooling is far greater than the need for heating and in general larger overhangs will be more useful (particularly during summer storms to keep natural ventilation operating). The amount of shade needed will vary from house to house depending on the area and type of glass, solar gains from windows in other orientations, the extent of cross ventilation and the amount of thermal mass in the building.
Houses in Brisbane typically need to be cooled more frequently than they need to be heated.
As a result, eaves always improve the rating of the house. On west windows the deeper the eave the better, however, the benefit of deeper eaves beyond 1.0m is small for north windows. This is because the sun is more easily shaded on north windows due to its higher elevation in the northern sky in summer.
Eaves will block summer sun (which sits higher in the sky) while still admitting winter sun (which sits lower in the sky).
Eaves and Orientation
If possible, you should build or choose a home that takes orientation into account. The orientation of your home relates to the way it is positioned on your block of land. A carefully oriented home in the cooler southern states of Australia will exclude hot summer sun and take advantage of breezes and winter sunlight.
Correct orientation will depend largely on your local climate, but as a general rule, a house that runs 15°W-20°E of true or ‘solar’ north is considered to have an ideal orientation. The size of your Eaves will depend on where in Australia you’re building. For example, if you reside in Queensland or Darwin for example, you’re likely to need eaves that keep the sun out year-round.
Homes without Eaves
Not all homes have eaves. Some styles are built without them, sometimes as a means of making better use of narrow house blocks. Roofs that incorporate eaves are heavier than those without. As a result, the inclusion of eaves on a home is a major design consideration that also affects the other load bearing elements like the walls and sub floor. In most cases, eaves are not simply an optional extra – they need to be accounted for at the design stage for your home.
Conducting a NatHERS Assessment during the design stage of your home is a great way to determine the most appropriate size of all your eaves and other shading devices.
Alternatives to Eaves
Homes designed to suit the climate in most parts of Australia should ideally include a roof with eaves. If your home does not have eaves though, there are some alternative methods for protecting your windows from the sun. These include:
- Other fixed shading (e.g. awnings or pergolas)
- Shading with plants
- Solar films for windows
- Low emissivity windows
Tip
Eaves, awnings, and other ways to shade windows from the outside are far more effective than curtains and blinds, because they prevent heat from being transferred through window glass.
By preventing direct sunlight from hitting a window, these options offer a simple and effective way to reduce the amount of heat through windows. External window shading is an important part of passive house design and making sure that the amount of light isn’t too badly reduced is a great way to help keep heat at bay.
Retractable Awning
A retractable awning extends the comfort of your home to your outdoor space. By choosing a motorized awning, you can create instant shelter with just the touch of a button, protecting you from light rain and glaring sun alike. You’ll enjoy spending more time outdoors on your deck or patio.
Protection from the environment plays an important part in the thermal comfort and durability of houses, in both cool and hot climates. A simple method is to extend the roof well over the external walls of the typical house to form an eaves overhang or, if further extended, a verandah.
Incorporating eaves and overhangs provides a number of important benefits, into your structures such as:
- Shading walls from excessive solar gain
- Keeping direct sun off the window glazing
- Allowing windows to be left open for comfort ventilation while still providing shelter from rain and
- Protecting large areas of walling from rain, keeping wall surfaces relatively dry and free from staining and mould growth.
