When building a house, commercial building or renovating there is a requirement that it complies with the Building Regulation's requirements for energy efficiency and that it achieves the required energy rating.
For houses this is usually done by an external consultant who uses computer software to model the house and produce a report. In Victoria there is a requirement for a 6 star rating for new houses and an equivalent rating for renovations that takes into account the percentage of new area.
Energy rating goes beyond just a requirement of the Building Regulations and based in good design principles. It is a regulation that ensures that the house not only uses less energy, but is also more pleasant to live in. The rating takes into account orientation, area and location of windows, shading, building materials and their thermal values, artificial lighting power consumption and heating and cooling equipment efficiency.
In regards to the orientation and windows, the principles of passive solar design play a large part. Refer to our article on Passive Solar Design. One of the factors that plays a major part is the size and location of windows. Generally our clients, as well as us, like large full height windows that take in the view and add light to the houses interior, blurring the divide between the outside and inside. However they are the major contributor to heat loss and gain. You only have to put your hand against a single glazed window in winter or stand next to it to feel the heat literally flowing out through the glass. Windows on the North are best suited to contributing to energy efficiency - allowing passive solar heat gain in winter. Windows on the South only loose heat and don't have the benefit of winter heat gain. As a rule of thumb once a design has an area of double glazed windows that is about 30% of the floor area extra measures are needed to be taken to get to the 6 star rating, such as higher insulation values and performance glass. Traditional houses have been able to achieve the 6 star rating by having a lesser number and smaller windows, this of course reduces light and views.
We design our buildings taking into carefully taking into account the placement and size of windows. They are placed to orient to the views, let in light to minimise the use of artificial light during the day and sized based on their location. Most of this is common sense, small windows in the laundry and bathroom areas, medium sized windows with higher sills in bedrooms to allow for furniture placement under them and to provide privacy, larger windows in lounge and common areas. As the windows get towards the limit of what is allowed there is a requirement to increase their performance with double glazing, performance low-e glazing and insulated frames.
A building's materials are also important. Insulation plays an important role as well as the use of thermal mass, this is most usually in the form of a concrete slab. These help regulate the internal temperature, and stop rapid internal temperature changes when the external temperature fluctuates.
Other factors that have recently been taken into consideration are the use of LED lighting, and the reduction of recessed downlights that allow heat to flow into the roof cavity.
An energy rating is usually conducted at the end of sketch design to ensure that the number and size of windows can be achieved before we start documenting the house and make the required changes if any. The report is a minimal cost - usually around $500.
At the end of the day the requirements of the rating make the house a much more pleasant environment to live in. You have to heat and cool your house less and this is especially noticeable during Spring and Autumn where you can rely on the heat of the day to keep your house warm at night.