Elements of a sustainable building envelope

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Heat pump or solar hot water system Light or green roofs Solar photovoltaic (PV) systems Insulation Windows and skylights Eaves and shading devices Sustainable construction materials Recycling/Reusing greywater Heat-reflective paints Image Map

Sustainable construction materials

Locally sourced materials and natural materials

Consider transport miles from quarries to distribution centres and to the site for materials you use for cladding, flooring, roofing, framing, windows, doors and outdoor structures.

Natural materials found in abundance such as clay, lime, straw, hemp, bamboo etc. can help to provide a beautiful finish for your home and are good for your health and the environment. However, make sure these meet the Building Code of Australia requirements and will check with your insurer that this will not void your home insurance. 

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Renewable materials

Soil is a vulnerable resource. One hectare of topsoil (the most productive soil layer) can contain up to five tonnes of living organisms and because it can take more than 500 years to form a two centimetre thickness of top soil. In practical terms it is considered to be non-renewable. Topsoil should kept separate from fill and construction waste and re-used in landscaping works on completion.

Quarried materials such as gravel and stone are also non-renewable resources and their extraction can lead to vegetation loss, ground and surface water pollution and soil erosion. Bamboo, on the other hand, is a renewable resource that grows quickly without the help of pesticides and chemicals. So is cork. It is a type of bark that is harvested while leaving the tree intact. Opting for materials from renewable sources or recycled materials can help reduce demand for the virgin product.

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Salvaged materials

Second-hand materials sourced from old buildings and structures such as bricks, plumbing fixtures, and hardware, doors and windows, may be able to be reused. For example, broken bricks and roof tiles can be turned into rubble as a base for a driveway. Be creative - you could reuse previous roof beams as treads for your new staircase! 

However, make sure materials you reuse are safe and efficient. For example, test for asbestos and lead paint, and when reusing old windows or toilets, and consider potential trade-offs of energy or water efficiency when using salvaged products.

There are a number of recycled timber suppliers around Sydney including Ironwood Australia, Heritage Building Centre and Recycled Timbers. A search online for 'excess building material' yields a number of useful websites and organisations.

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Low embodied energy materials

Homes built with lightweight materials such as timber and fibre-cement composite products can have low impact on the site topography. They also have low embodied energy when compared to brick homes. Such materials can be tough, resilient and durable against fire, termite and moisture damage, much easier to insulate, as well as more cost effective. Higher embodied energy materials such as brick and concrete may be justified if it contributes to lower operating energy. For example, a concrete slab floor in the living area which receives a lot of sun would be a better option as it helps in winter warming and reduces heating costs.

FSC-PEFC.jpgTimber is more sustainable due its lower embodied energy and because it stores carbon. Make sure your wood is recycled or chain-of-custody certified. Chain-of-custody certification schemes include the Forest Stewardship Council (FSC) and the Programme for the Endorsement of Forest Certification (PEFC).

Any timber that is not FSC-certified or not Australian plantation-grown should be avoided. The order of preference in choosing timbers could be:

  1. Recycled timbers
  2. FSC-certified Australian plantation or native timbers
  3. Non-certified Australian plantation timbers
  4. FSC-certified timbers from other countries.

Reconstituted wood-based products such as laminates and gypsum plasterboard are other low-embodied material options. Choose environmentally accredited options as far as possible. Make sure all woodwork is finished with natural oils that have no volatile organic compounds (VOC).

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Some of the newer engineered wood products are:

  • Cross-laminated timber (CLT) - Layers of timber glued together with the grain alternating at 90 degree angles for each layer gives this timber optimum strength. Can be used as a panel product for ceiling, floors and walls.
  • Laminated veneer lumber (LVL) - uses multiple layers of thin wood assembled with adhesives. Being made with controlled specifications makes it stronger, straighter, uniform and less likely to warp, twist or shrink. Can be used for permanent structural applications including beams and rafters.
  • Glulam (glued laminated timber) - Can be curved or straight and is often used as structural beams. Though strong as steel or solid timber, this is much lighter. Can produce large sizes and longer length members.
  • Bio-composites are materials made of natural fibres, like flax and hemp, and natural resins made from the by-products of agricultural processing of corn, sugarcane and other crops.

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Eaves and shading devices

Eaves, verandahs, vertical screen or thick planting, on the north, east and west side of your house will help protect against heat load from these directions. Eaves to the windows should be wide enough to exclude the summer sun but allow sun in the colder months.

North-facing verandas can benefit from pergolas, adjustable shade sails or structures with louvres which can be opened or closed as required. Planting deciduous vines over the northern pergola and trees that lose their leaves in winter on the northern side provide summer shading while maintaining solar access in winter. A porous knitted shade cloth can be a simple way to keep the hot sun out and allow daylight indoors.

Learn more

  • NSW Government - BASIX: Shading
  • Australian Government - Your Home: Shading

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Windows and skylights

Windows allow daylight into a room and this reduces the need for electric lighting. However, it should also be factored in that a window also allows more heat to enter and leave a home.

Along with the effective use of eaves and shading, you can reduce this loss by choosing energy-efficient windows. Use the WERS (Window Energy Rating Scheme) Guide to compare thermal efficiency.

Gaps around an ill-fitted window frame can let more heat in/out than the window itself. There are various sealing products available at hardware stores which can be used to seal gaps and eliminate draughts. See Section on Air-tightness in Design Aspects.

An average timber-framed double-glazed window has an R-value of 0.3 while the minimum for a BCA-compliant wall in Sydney is 2.8, which is about ten times that of a window. So a well-insulated wall is always better than the most efficient window. It is good to remember this when you are sizing up your windows. A good view does not necessarily mean floor windows - you can sometimes frame a view better with a smaller window!

Timber-framed windows are better than aluminium windows at restricting heat flow through the frames but thermally broken* aluminium frames or uPVC@ windows can also be good options to look at.

Points to consider:

  1. Positioning of windows - Most windows should face north. On the southern and western side of the house, you can plan for higher windows (clerestory) covered by eaves. In summer, you should open these high windows to let cool breezes blow out the heat of the day. Minimise windows in east and west elevations as these are exposed to morning and afternoon sun for longer periods of time. Louvered windows are good to direct the air flow towards the occupant of the room.
  2. Skylights can bring in natural light into corridors and dark rooms/areas without windows. Better energy levels for residents, especially children and the elderly, are proven benefits of daylighting. Devices such as solar tubes and solar domes can also reduce the need for artificial lighting.
  3. Double glazing – Air space between two pieces of glass is a good thermal insulator. It also helps in noise reduction. When two sheets of glass are separated with sealed edges and an inert gas such as argon is filled between them, heat loss is reduced. Glass with a low E-coating# is even better.

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Retrofitting double glazing on windows is possible though it does not come cheap. Window films and systems such as Magnetite allow you to keep the existing windows, especially important in heritage areas. Another low cost solution is a thin film of clear plastic press-fixed with double-sided adhesive tape to the rebate in the window frame.

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* Thermal break: a material of low thermal conductivity that is inserted between members of high conductivity in order to reduce heat transfer.

@ uPVC is a flame retardant material commonly used in fire risk areas.

# Low emissivity-coating is applied to the external side of the internal glass. It reflects back into the interior the long-wave heat energy from the interiors while allowing the sun’s short-wave energy to enter the house during sunshine hours. 

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Insulation

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Insulation is the single most effective item you can add to improve the energy efficiency of your home. Insulation acts as a barrier to heat flow and is essential for keeping your home warm in winter and cool in summer. It also has sound-proofing qualities and is useful between floors in double storey homes.

There are two main types of insulation: bulk and reflective. Bulk insulation stops heat flow by trapping air in small air pockets. Reflective insulation resists radiant heat by reflecting or not emitting heat.

Energy efficiency assessors can detect insulation inefficiencies, dampness and air leakages using tools such as thermal imaging and blower door tests. Depending on their findings you can patch up or install new insulation.

Roof insulation is easier to address due to accessibility but you can take the opportunity to insulate walls during renovations or replastering. Retrofitting under-floor insulation can be achieved if there is enough room to access and install it. Insulation can also be stapled under suspended floors if accessible. Carpeting a bare floor also helps to insulate a home. Concrete slabs usually need minimal insulation as it uses the insulating value of the ground below.

Few common building materials have insulating value, but options such as aerated concrete blocks, fibre-reinforced gypsum, hollow expanded polystyrene blocks or rendered straw bales offer good levels of insulation, with little or no additional insulation needed.Insulating materials.jpg

Regardless of the material you use, you can compare their impact by comparing R-values. R-value is a measure of how effective an insulation material is at stopping the transfer of heat. The higher the value, the better its insulating property. The recommended insulation level for Sydney’s climate is 4.1 for roof/ceiling and 2.8 for walls.

Determining the best insulation for your home depends on a number of factors such as:

  • location - which determines the bushfire risk or BAL (Bushfire Attack Level) rating of your property
  • access to roof space and whether the roof is flat or pitched
  • the use of roof space for storage
  • the local climate, and
  • health impacts, especially for allergy/asthma sufferers.

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Once you have taken these into consideration, choose the most environmentally friendly product possible - ask about recycled content and how easily the product can be recycled after use. Some of the insulating materials that are low energy to manufacture are sheep wool, cellulose fibre (made from recycled newsprint), cork, straw and a hemp/lime mix.

Some examples of sustainable insulating materials

  • Insulation which has a high percentage of recycled material, e.g. polyester insulation using recycled PET (the plastic commonly used in drink bottles), cellulose fibre insulation containing recycled paper and fibreglass insulation containing recycled glass.
  • Non-combustible and non-flamable insulation products.
  • Structural insulated panels (SIP) which can provide greater air-tightness than a standard timber insulated stud wall of the same thickness.
  • Reflective glasswool insulated blanket (sarking) is effective at stopping heat transfer in and out of the roof space.
  • Wafflepod slab (a concrete slab that has a layer of insulation under it to reduce unwanted heat transfer to the earth) is a good floor insulation option.
  • Insulated plasterboard products are space efficient as they have a thin profile but maintain energy efficiency.

Insulation issues to be aware of:

  • Some insulation products (eg. polystyrene, polyurethane blocks and panels and PVC) may not be suitable in bushfire prone areas as they could be exposed to heat or flame in external walls.
  • Be careful when renovating old homes which may have loose filled asbestos material. If a home was built or renovated prior to 1987, it is likely to contain asbestos and it could be anywhere: under floor coverings such as carpets, linoleum and vinyl tiles, behind wall and floor tiles, in cement floors, internal and external walls, ceilings and ceiling space (insulation), eaves, garages, roofs, around hot water pipes, fences, extensions to homes, garages, outdoor toilets, backyard and farm sheds, chook sheds and dog kennels.
  • We need to balance the benefits of thermal performance and issues such as build-up of moisture. For this air flows within the house need to be managed and you should be able purge hot air. See section on Ventilation.
  • Care needs to be taken not to create the perfect warm, dry, dark environment for white ants. It is best to leave joists exposed.
  • Insulation can help to control the cold as much as a polar fleece jumper. If it is windy, you would still feel the cold. If air-tightness of a house is not taken care of, the benefit of having a well-insulated house wanes. If the southerlies can blow into the house, insulation will be of little use.
  • Reflective foil insulation will not provide any benefit unless an air gap of 20 to 30 mm is fixed in place. If this is not possible, use bulk insulation.

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Solar photovoltaic (PV) systems

Use of renewable and non-polluting energy sources such as solar power is economical and environment friendly. The initial cost of installation could be high but you could be eligible for rebates. When building new, even if you don’t plan to install solar panels or solar hot water, if you pre-wire and pre-plumb, you can save thousands on a later installation.

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Light or green roofs

Green roof.jpgReplacing a traditional roof with a green roof can offer good insulation for a house while also slowing water run-off. Roofs may need to be strengthened if the design load bearing capacity is not sufficient to hold the additional weight of a green roof.

Where a green roof is not an option, a white or light-coloured roof could be considered. Lighter colour roofs are able to reflect more sunlight and therefore more heat while darker roofs absorb more heat. However, do consider issues of glare for neighbouring properties and the measures you can take to reduce this such as matt finishes, altering the roof pitch or landscape screening.

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Heat pump or solar hot water system

Since hot water can account for up to a quarter of household energy bills, reducing your hot water use and using renewable energy sources, such as the sun or ambient air, to heat water can greatly contribute to reduce your environmental impact in this area.

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Heat-reflective paints

Using heat-reflective paints on walls and roofs may help cut to heat gain, though it comes at a cost premium. A review by the Australian Solar Council showed that though heat reflective paints do reduce the surface temperature when compared to a standard paint of the same colour, its benefits are smaller for white or lighter colours. Using lighter shades of paint itself is sufficient for solar reflectivity but where you want a darker colour palette, using heat-reflective paints helps.

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Recycling/Reusing greywater

Greywater is wastewater from your home that comes from the bath, basin, shower and laundry. This can be  treated and used for irrigation, toilet flushing and washing machines. You need to obtain approval from Council to operate a greywater treatment system. Greywater can be diverted for reuse, or treated and reused to water gardens, wash clothes and flush toilets.

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