Marrying the designed performance with the actual construction outcome is essential to achieve a low-energy building and deliver real savings which ultimately win the consumer vote for energy efficiency.
In the Australian building science community there are several strongly established concepts that govern the performance of a thermally-efficient, low-energy building. During the post-construction testing of CSR House, several principles for designers to take into consideration for high levels of efficiency and performance were identified. These key concepts are surprisingly and frequently missing from the design processes and construction methods used in Australia.
Heat: Managing the transfer of heat through the whole building envelope is well understood at a theoretical level, but installation practices need to be managed better to ensure consistent coverage of insulation.
Air: Air can leak around window frames, construction joints, wall penetrations and many more locations inside a building. This can double or even triple heating and cooling requirements. Simple techniques used on-site can eliminate the majority of air leaks.
Moisture: Controlling moisture requires careful consideration of how heat and air travel through the building envelope. If humid air is allowed to pass freely between living spaces and construction cavities the water vapour in the air can condense on cold surfaces.
CSR’s Scott Clarkson says, “Designers, builders and trades need to make sure critical construction details are managed appropriately on-site to suitably control these three variables.
Clarkson says CSR has also identified key areas in typical residential construction which do not control heat, air or moisture appropriately:
- The thermal performance claimed on product packaging assumes no gaps in bulk insulation. Often insulation gets moved or shifted for services and not replaced, severely reducing the effectiveness of ceiling insulation.
- Reflective foil applications achieve system R-values based on the assumption there is NO air flow across the reflective surface, reflective membranes therefore require all joints to be fully taped and penetrations to be sealed with an impermeable adhesive patch.
- Eighty per cent of energy lost through a slab will be lost through slab edge conduction. In warm or temperate climates this is of less concern than colder climates such as Tasmania, Victoria, ACT and Alpine regions requiring slab edge insulation.
- Commonly there are air leaks at the top of architraves and around reveals, including between window frames and building framework to which windows are fixed.
- Timber flooring and skirting boards with large gaps can have a huge impact on the ability to hold warm and cool air in the living space.
- Air leakage around an air conditioning diffuser or extractor fan (even with a damper) can impact the thermal performance of the building.
- Downlights require holes to be cut in insulation plus they often cause considerable air leakage.
- Bathroom and laundry exhaust fans that vent to voids or roof spaces cause high levels of humidity in these areas, with the humidity often condensing and can cause mould, rotting or corrosion.
- Incorrect paint use on rendered surfaces can “blind” the building skin and not allow water vapour to dry out; this too can cause mould, rotting or corrosion.
CSR invites designers to contact the CSR Knowledge Centre and familiarise themselves with the latest information on these key concepts.
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