Choosing to live in a high fire danger area is one thing, but wanting to make it energy efficient on a west facing slope added more challenges. Sarah Bachmann discusses the challenges.
Around two years ago, my partner and I made the decision to move back to Adelaide after 16 years in Sydney. Deciding to resettle in the Adelaide Hills suburb of Belair, we looked to buy a house, but were adamant the house must be energy efficient, durable and safe from bushfire. There weren’t any, so we decided to build.
The block we decided on has magnificent views over Glenelg and the Southern Adelaide Coast and fronts right onto the band of bush that forms part of the Mt Lofty Ranges and marks where the Adelaide Hills begin.
We thoroughly investigat ed the choice of construc tion options. Even though I have a natural bias towards precast concrete, I kept an open mind and we consid ered many and varied alter natives, from rendered block to various forms of insulated concrete forms. Not one of these systems ticked all our boxes of energy efficiency, durability and fire resistance.
Blocks, for example, would need to be rendered on the outside and then insulated and lined on the inside, and with the thermal mass being on the outside of the wall structure, we couldn’t engage solar pas sive design principles.
Reverse veneer might have ticked the energy effi ciency box, but it didn’t tick the durability box (and would require maintenance), nor the fire resistant box. Whilst insulated concrete forms did have a high R- value, again, we would not have been able to employ solar passive design and had concerns about the exterior durability and fire resistance.
Every time we reviewed an alternative product, we kept coming back to one of the newer products which are being offered by the precast concrete industry in Australia — precast sandwich panels.
Precast sandwich panels are comprised of a thinner precast outside skin (typically 70 mm to 80 mm) and a thicker precast structural inside section (typically 100 mm), which are held togeth er by non-thermally-conduc tive ties and with an insula tion layer in between.
The system allows the out side skin to expand and con tract with fluctuations in tem perature, without compro mising the structural effec tiveness of the building. It also maximises thermal mass benefits by having the large volume of unlined painted concrete on the inside of the building. Because of the high quality of the precast finish, all that is required on both surfaces is staining or painting.
Double glazed windows have also been utilised and mechanical shading both inside and out, which will allow shading of the western glass from the afternoon sun. Eaves on the north face prevent ingress of the sum mer sun but allow entry of the lower winter sun. There are minimal windows on the south side of the house.
We have also staggered the living areas on the west ern face to provide sun access from the north. During the day, the heat from the sun passes through the windows and is absorbed into the thermal mass interior walls and into the thermal mass concrete slab-on-ground (most of which will be tiled). At night, that same heat is released slowly back into the interior of the building. When placed on the inside, con crete has an ability to absorb and release heat slowly, allowing the inside of the building to remain at a fairly constant temperature all year round.
Precast concrete sandwich panels, together with CSIRO fire-tested and rated double glazed windows and a very well insulated Colorbond roof will give us a highly energy efficient, fire resistant and durable home. To fur ther reduce the home’s use of resources, photovoltaic solar panels will be used, which are expected to gen erate sufficient electricity for the dwelling’s use plus return power to the grid.
Two water collection tanks (with a capacity of 112,000 litres) will collect rainwater and stormwater and will sup ply the majority of water needs. Greywater will also be treated and re-used on the drought-tolerant perma culture-style garden.
A solar hot water system will be installed and an energy efficient air-conditioning sys tem will used, while in-slab hydronic floor heating will further enhance the thermal mass benefits of the floor. And from a fire safety per spective, gutter guards and in-ground and roof sprinklers will be installed. All light fittings and appliances will also be energy efficient.
Sarah Bachmann is executive officer of the National Precast Concrete Association Australia. For more informa tion about the project go to www.hillsideproject.net
