Design standards of energy efficient housing aims to minimise energy consumption of non-renewable resources for heating and cooling and hot water. The associated advantage of this is to reduce costs borne by the householder. Cost effective energy efficient housing is usually easiest to achieve at the initial design stage by integration of the dwelling and the site. This allows maximum use of natural elements such as solar access and air movement, and enables the development of interior design elements to produce a high degree of comfort while minimising and conserving energy use.
Although ACTHERS (ACT) is based on the potential of the design to reduce energy use, the behaviour of occupants and the energy efficiency of major appliances are also very important in overall energy consumption.
The Scheme is based on extensive computer simulations of housing performance in various Australian climates. It focuses on insulation, orientation (of living areas and windows), air leakage and other design features to provide a comprehensive picture of the house's potential for reduced energy consumption. Design measures which achieve better energy efficiency include:
orientation north facing living areas with good winter sun access (extremely important design issue).
insulation appropriate R ratings of insulation where appropriate in ceilings, framed walls and under floors (eg concrete slabs and suspended floors).
air leakage draughtproofing around fireplaces, windows and doors
design features such as ceiling height, north facing windows in living areas.
floor type slab on ground, suspended slab or timber.
zoning internal zoning of living areas with ability to segregate areas for optimal heating and cooling.
glazing type used for various orientations (eg. smart glass, double or tinted), and the optimal percentage of windows appropriately oriented and designed for reduction of heat loss in winter, and for shading in summer thermal mass use of building materials with high thermal mass for floors and internal walls, and use of trombe thermal mass walls.
width of eaves optimal widths of eaves to accommodate various aspects.
cross ventilation reduces residual heat in summer and adds benefit of diminishing fungus and bacteria in carpets and curtains.
common walls especially in multi-unit/townhouse developments.
Windows are a critical element in energy efficient house design, as unprotected single glazing allows the rapid transfer of heat into a residence in summer, and out in winter. The larger the window, the greater the transfer of heat. As living areas are those most commonly used, thermal comfort in these areas is important.
Where it is not possible to secure northern window access for every room, priority should be given to locating as many as possible of the living areas on the northern side of the house. These areas need to be comfortable. They should optimise natural light during winter and be shaded in summer, improving overall energy efficiency.
In order to conserve captured heat within living areas, the house design should provide for doors which separate the living areas from bedrooms and service areas. Grouping rooms with similar uses will also assist in making the most efficient use of heating and cooling systems. South facing windows are useful for assisting cross flow ventilation, particularly in summer. However, their use should be carefully considered, especially with respect to their internal coverings. Without adequate insulation treatment, the south facing windows may also contribute to heat loss.
East and west windows if too large, may gain large amounts of unwanted heat during summer and lose heat during winter. Selection of glazing and window treatments for summer shading and winter protection is critical to the overall performance of the residence. With its ability to reduce the amount of energy needed to heat or cool a house, insulation is an important element of energy efficient design that can be added to a home.
The BCA code has set the parameters for energy efficient design as follows:
for Class 1, 2, 3 and 4 Buildings (ie Residential - Single detached dwellings and multi-unit developments), the standard required is an ACTHERS Rating of 4 stars.
for extensions to those Buildings, either an ACTHERS 4 star rating, or comply with the following standards:
concrete floor; or
timber floor with an R rating of 1 including carpet; and
R3 insulation material in the ceiling space; or
R2 insulation material (+ optional sarking R0.5) in exposed raked ceilings; and
WALLS (see exemptions in (b) below):
R1.5 insulation material in the external wall space.
NB: Ceiling and underfloor provisions exempt most buildings.
EXEMPTIONS: The requirements of this Part of the BCA do not apply to the following types of construction:
a ceiling or underfloor space where unrestricted access for the installation of insulation will be available after the completion of construction; and
cavity brick, earth wall construction, ashlar stone or other masonry walls which have a thickness (excluding any cavity) of not less than 180 mm.
Insulation assists in retaining any energy input to a residence, whether for cooling or heating, and whether achieved by solar access or an appliance. This reduces the rate of turnover in the replacement of that energy. The use of building materials with high thermal mass (the ability to store heat) is also of value to an energy efficient home. Concrete floors and internal masonry walls are examples of materials which assist in the regulation of internal temperatures.
High thermal mass is particularly important in climates where summer an winter temperatures vary greatly, and large differences occur between minimum and maximum daily temperatures.
Unwanted or uncontrolled ventilation or air leakage may add significantly to the costs of cooling, and especially heating a home. The use of weather strips and door seals will improve the overall performance of an energy efficient house, while reducing energy consumption and costs.
However, ventilation is also an important component for regulating internal temperatures during summer and for allowing fresh air into the house to control dampness and mildew if required.
Cross flow ventilation during summer is enhanced by appropriately placed windows and doors on all sides of a house. Other elements may further add to the energy efficiency of a home. However, these do not form part of the energy rating assessment. These include:
an efficient and flexible heating system.
an energy efficient hot water system (such as solar).
use of energy efficient lighting and appliances.
landscaping sympathetic to the microclimate of the house.
On average, an energy efficient home is up to 5 degrees warmer in winter and up to 10 degrees cooler in summer. As well as being more comfortable all year round, an energy efficient house also has much more natural light in areas most commonly occupied, including direct sunlight which does not detract from internal thermal comfort.
The principles of energy efficient design do not limit housing choice, but rather create opportunities to use a variety of design features to produce an attractive and functional home.
There are 6 special conditions under which an exemption may be claimed from achievement of the minimum house energy rating requirements for new houses. Where one or more of the special conditions apply, approval is subject to provision of ceiling and wall insulation, and under floor insulation to timber floors:
block geometry - orientation or shape of block such as to preclude the northerly orientation of the house, defined as 340o to 30o.
block overshadowing - adverse slope of block, existing obstruction or planned or existing development resulting in overshadowing of northerly windows.
block topography and geology - slope, drainage or geo-technical constraints such as to preclude the adoption of slab on ground type construction.
novel construction - where the prescribed assessment techniques do not reliably assess the thermal performance of the construction being adopted and there are prima facie grounds for believing that the prescribed techniques significantly underestimate the construction’s performance.
conflicting guidelines - lease and development conditions, territory plan guidelines or any other imposed restriction eg. heritage requirements, which preclude the attainment of the minimum rating requirement.
uneconomic requirements - where it may be demonstrated that the attainment of a 4 star rating would require additional expenditure which is not cost effective.