Passive Design takes advantage of the climate to heat, cool and light interior spaces. Good passive design takes into consideration the site orientation, and has a well performing building envelope. Well designed ventilation and shading can significantly reduce energy demands on heating, cooling and lighting.
The following information refers to residential and small-scale commercial buildings.
Orientation of a building is important for receiving warmth in winter, breezes in the summer and making the most of the natural landscape and views. In Victoria there are far more days when heating is required, than cooling in residential and small-scale buildings and therefore orientation and window placement is biased towards the winter mode. However with climate change and rising temperatures it is really important to minimise the risk of overheating.
The following window orientations are recommended:
North Facing Windows – Ideal for letting in low winter sun to heat interior spaces / and are easy to shade in summer with horizontal shading.
East Facing Windows – Good for letting in low morning sun / require vertical shading in summer
South Facing Windows – Not ideal for main areas, because no solar gains can be received in winter / no shading required
West Facing Windows – Can allow low winter sun in winter, however not ideal in summer as hot afternoon sun can cause extreme overheating within building / require vertical shading in summer
On an open site it is generally best practice to face main living/working areas towards the north and some to the east, whilst placing service areas towards the south and west. However, orientation is heavily dependent on the site, client needs and function of the spaces.
The building envelope is vital in retaining heat in winter and excluding it in summer, whilst also providing waterproofing. To achieve optimal passive design, it is ideal to have a layer of un-interrupted insulation covering the entire building envelope, thus insulation in the walls, ceiling/roof and under the floor. Bulk Insulation is the most effective form of thermal insulation because it has millions of tiny little air pockets, which limits heat transfer.
Meticulous sealing of the building envelope is required to minimise air leakage. Air leakage in conventionally built houses houses can account for up to 15-25% of heat loss in winter, which significantly increases your energy bill. In Passive House Standard buildings an airtight layer is installed on the inside of the building envelope to ensure that air does not leak out of the building envelope.
Good quality windows should also be part of a good building envelope. Windows account for very high levels of heat loss and heat gain and are the weakest part of the building enveloped.
It is therefore vital that your windows are well orientated, appropriately sized and have good thermal performance properties. We recommend the use of double glazing, well-sealed frames, and/or special coating.
Solar Radiation entering the building through windows is a major source of heat gain in the summer. It is therefore vital that windows are appropriately shaded to stop solar radiation entering a building.
Horizontal Shading – North facing windows are easy to shade with horizontal shading, which stops high summer sun from entering the windows.
Vertical Shading – East and West facing windows are not as easy to shade, because morning and afternoon sun is low in the sky and therefore vertical shading (blinds, louvers, shutters) is required.
There are many methods of shading such as roof eaves, adjustable awnings, shutters, deciduous trees and vines.
Good ventilation is also a method of cooling down interior spaces, especially in summer evenings when there is a drop in temperatures. It is best to utilise cool winds coming from the south and to encourage them to flow through a house via cross-flow ventilation and stack-ventilation.
A Heat Recovery Ventilation (HRV) System can also be installed in the house, which brings fresh air into the house and transfers heat from outgoing air. This means fresh air enters a house and stale ait is exhausted, but on the way out it conditions the incoming fresh air, thus saving energy in heating and cooling this air. As buildings become more insulated and airtight, we need to ventilate them more to indoors spaces have adequate fresh air. It is unsustainable to rely on leaky, poorly sealed building envelopes to bring outdoor air into our buildings.
All Passive House Standard certified buildings require HRV systems. For more information on HRV visit the Australian Passive House Association website.
Thermal mass refers to a material’s ability to hold and release heat. Building materials that are high in thermal mass tend to be of high density such as brick, concrete and stone.
Thermal mass can have a positive affect when used internally, for it can help regulate temperatures and act as a heat sink in winter. However, if thermal mass materials are used for external walls and not insulated, heat will be absorbed by these walls and slowly be released to the cool exterior in winter and the opposite will occur in summer, which will leave indoor environments uncomfortable.
When choosing external materials, it’s very important that we consider the thermal properties and how they can enhance or hinder the passive heating and cooling of a building.
Maximum efficiency of Passive Design is achieved when users understand how to operate the building to regulate indoor temperatures and comfort levels, or alternatively when some aspects of the building are automated. Natural Elements mission is to educate users on how to operate the building and provide support to ensure user comfort.
The Performance Gap
Passive Design is currently a legal requirement for new residential buildings which are assessed under the NatHERS star rating scheme. The minimum requirement asks for 6 stars, however it is widely known in the industry that what is currently being built does not always meet 6 stars and is often performing far below the desired benchmarks. This is known as the ‘performance gap’.
The only way to ensure buildings perform well thermally is for the architect and builders to understand the basics of thermal performance and building physics. The other option is to build to Passive House standards to ensure there is no performance gap.
Natural Elements is well versed in Passive Design principles and can help client understand how their house can best utilise and implement the strategies listed above.
Australian Passive House Association (APHA),
Your Home, The Australian Government,