In summer, a lightweight steel roof can cause less heat to be radiated into your home as it cools down at night. In winter the same steel roof, properly insulated, helps keep the heat inside. Regardless of climate or weather, the right roof can prove to have energy saving features through reduced cooling and heating costs.
Thermal efficiency is an important consideration when building a home. One important component of thermally efficient design is the selection of an appropriate roofing material. A roof made from COLORBOND® steel or ZINCALUME® steel can contribute to the thermal comfort of a home and to reduced cooling and heating costs.
Energy ratings are now commonly used as selection criteria when purchasing household appliances. When designing a home, it is just as important to consider details such as orientation, roof colour, insulation and roof shape, as these can all influence the energy efficiency of the home.
Some important aspects that can influence the level of summer and winter comfort provided by a home are shown here:
1. Solar Design
A dwelling with true north orientation, with its living areas at the front, takes advantage of the warming winter sun. During summer, when the sun is higher in the sky, correctly designed eave-overhangs will ensure less sunlight enters through the north-facing windows.
If windows and doors are positioned to allow cooling breeze to circulate, the net effect is a cooler home. The use of louvres can be good to promote air movement on hot days.
3. Thermal Mass
Thermal mass is the ability of a material to store heat. If thermal mass is to be designed into a home, it is best included in floors and internal walls, since these can be warmed during winter days and release heat in the evening. These surfaces can also be protected from the sun in summer with the use of appropriate windows and eaves. There is no such control for the roof, so it is generally considered good practice to use low thermal mass in roofing systems. A roof made from ZINCALUME® steel or COLORBOND® steel is strong and light weight. It has a low thermal mass which means it cools down fast on a hot night and improves the comfort within the home.
Insulation in walls and ceiling spaces can affect the amount of heat entering or leaving a dwelling. Appropriate insulation detail will vary with roofing and walling material selection and location. The chart below shows the heat radiated through different COLORBOND® steel colours and demonstrates not only the benefit of light colours during warm periods, but also the increased importance on insulation when using dark colours in warm climates. (Assumptions used in steady state calculations: solar radiation of 850 W/m2, zero wind speed and 30ºC ambient air temperature.)