Govetts Leap Bach

This build incorporates numerous sustainable products within the interiors and exteriors. All the concrete was Insulated Hanson Bronze, which incorporates fly ash, slag, silica fume, recycled aggregate and uses recycled water during production, saving around 67KG of embodied carbon per cubic metre compared to traditional concrete. Hydronic underfloor heating is in the topping over the 100mm insulation layer. Colorbond roofing and cladding were employed for durability. All external walls have continuous 140mm mineral wool insulation, whereas the wing roofs have R5.0 and the entry roof has R3.0 mineral wool insulation. To ensure the home’s bushfire resistance, TBA Firefly Bal-Flame Zone wall sarking lines the external walls, along with Promat Weather Defence, which is a fire-rated breathable barrier with a recyclable core. Together with Proclima Intello wrap to the ceiling frame and interior studwork, an airtightness rating of 2.3 ACH was achieved. The internal walls are Austral Masonry Australite concrete blockwork, which have recycled content, require less mortar, and are lighter and more thermally resistant than traditional blocks. Zero VOC paint from Australia’s Ecolour is used throughout. The joinery is made from Plytech Green plywood, which is FSC and PEFC chain of custody certified, and uses bio-based lignin, a by-product from the manufacturing of paper, in lieu of standard fossil binding agents to reduce the product’s carbon footprint. Benchtops and window sills employ Paperock, made from layered recycled paper, bonded with phenolic resin. Paarhammer BAL-FZ rated timber windows and doors are fire-rated, Low-E double-glazed with argon. A Steibel Eltron heat recovery ventilation system (HRV) ensures constant fresh air, and was fitted with a F7 filter on the external vent and an additional filter to prevent bushfire smoke infiltration – making this one of Australia’s first homes to employ this technology. All appliances are electric, running off the generous solar panels and battery.

The building is borne out of all-electric, passive and environmentally sustainable design methods, and the curtailing of the footprint to a mere 110sqm, which is under 13% of the site’s total area. Given the bushfire risk posed to the site, an Asset Protection Zone around the dwelling was necessary for the safety of occupants, thereby resulting in the removal of some trees and vegetation, but due to the modest footprint of the home, this area was minimised. The massing of the dwelling was cultivated to afford privacy between neighbours while creating a sense of being immersed in the bush, hence the concept of two distinct wings with strikingly sloped roofs was developed to ensure both common and private spaces could stretch towards the north to promote natural daylighting and extend to the rear of the property towards the bush to foster biophilia. The bulk of the dwelling is elevated above ground level, ensuring minimal excavation and soil disturbance. The envelope of the structure meets natural ground level and the subfloor is filled to assist in the reduction of the dwelling’s vulnerability to bushfire attack, and maintained through the highly insulated external walls, the continued regulation and stabilisation of environmental conditions within the dwelling. This was one of the first houses that we’ve designed with Passivhaus principles in mind; the outcome, while never intended to reach Passivhaus certification levels, is expected to deliver an extremely efficient and thermally comfortable home facilitated through airtightness, insulation, optimal indoor air quality, reduced thermal-bridges, high performance windows and heat-recovery ventilation. This project demonstrates that a highly sustainable approach does not have to limit the possibility of a visually radical and contemporary architecture in extreme bushfire environments.
Govetts Leap Bach has been designed for resilience and endurance. By virtue of the detailing of the project, the external envelope is bushfire-resistant and the indoor environment will remain comfortable year-round and into the increasingly dramatic weather conditions forecast with climate change, thanks to a combination of old and new sustainable methods employed throughout the project. The HRV system with additional filters will ensure the air quality remains fresh, and the Stiebel Eltron instantaneous 3 phase hot water system will generate hot water only when required. The steeply stoped roofs serve the dual purpose of reducing the possibility of debris and ember lodgement, and increasing the roofs’ catchment area to funnel rainwater into the 10kL storage tank, which also acts as the Static Water Supply required by the Rural Fire Service. The 8 kw solar PV system with a 13.5 kwh Tesla Power wall containing a rechargeable battery system and energy storage device ensures the home will continue to continue to generate all of the electricity it requires, even in the depths of winter. Even the general layout of the dwelling is considerately designed into two primary wings - the sleeping, bathing and more private quarters within the western volume and the open plan living, kitchen and dining areas within the eastern volume - to ensure ample access to natural daylight and ventilation, with the division of zones also minimising any additional heating or cooling that may be required on occasion. The courtyard dotted with native fire-resistant planting and sandstone log terracing leading down to the rear yard soften the transition between the built and topographic elements to the rear of the dwelling, while also forming a non-flammable barrier between the dwelling and the bushland below.

The primary challenges faced in this project were central to the fact that the dwelling needed to be bushfire resilient, which comes with its own set of constraints and minimises the flexibility one has to employ varied sustainable strategies, but the very notion that the dwelling is fit for a bushfire setting is also one of its most sustainable aspects. The site was deemed BAL-40 to the street and BAL-FZ (Flame Zone) to the other 3 sides, thereby deemed amongst the highest ratings of bushfire risk in Australia, and paramount to our practice is providing sustainable architecture from procurement to post occupancy, hence it was a constant juggling act to pursue design objectives that push ‘green’ benchmarks while meeting stringent bush-fire regulations to ensure a modest dwelling could be situated on a site which retained the majority of its bushland. One example of the type of challenge we faced is with regards to reduced material selection – concrete is often utilised in bushfire settings for its durability, though it was difficult to access a sustainable concrete given the limited supplies currently on the market.

In early design development, NatHERs was the environmentally sustainable design benchmark utilised, with Govetts Leap Bach achieving 7 stars in thermal performance, as assessed by Eco Dweller Consultants. During later stages, the design was modelled by Plus Energy Living towards understanding the design strategies that could be utilised to further reduce the energy demand of the home towards becoming a Low Energy Building. Finally, the design was modelled in-house utilising the Passivhaus Planning Package (PHPP), and despite never striving for Passivhaus certification, the incorporation of these principles and strategies has ensured the operational energy of the home is net zero in accordance with Passivhaus Plus criteria. An important aspect of achieving a thermally comfortable home year-round with reduced reliance on artificial heating and cooling systems is to address thermal bridging, thus we specifically detailed the dwelling’s junctions to minimise heat loss and gain, and reduce condensation build up. For example, the thermal bridge was reduced at the slab edge, where the blockwork meets the structural slab, as we incorporated Foamglas between the blocks at a ratio of 3:1, reducing the thermal bridge rating of that junction by almost two-thirds – and together with the external insulation of the block walls and the isolation of the internal topping slab, our thermal modelling indicates this is a thermal bridge free junction. The HRV installed is also a Passivhaus Institute certified unit from Stiebel Eltron, with a heat recovery efficiency of just over 80%. Moreover, Govetts Leap Bach strives to meet Danish embodied carbon requirements (of 12kg CO2eq/sqm/year), with the final outcome resulting in 13kg CO2eq/sqm/year.

The brief for Govetts Leap Bach was to create a contemporary and sustainable home that engaged with the bushland setting. The clients called for a simply designed dwelling with outstanding architectural character, which despite the slight oxymoron, we feel we delivered. The site was originally a vacant bush block, with access to power, internet and telephone services from the main road, as well as access to potable water and sewer infrastructure. Intent on minimising the impact to the site, the clients suggested a floor plate area of around 100sqm – an opportunity we embraced, ultimately creating a modest home of 81sqm in floor space, with a footprint 110sqm. A single storey space was specified to afford aging in place, and minimise any impact on the bushland and neighbouring properties. With two immediate and developed residential dwelling neighbours to the east and west, and an abutting lot to the south, it was therefore critical to balance optimisation of views with visual and acoustic privacy. We understood the kitchen would be the heart of the home, the space in which our clients would spend most of their time as well as where entertaining would primarily take place. As such, it was crucial to afford an open plan kitchen, living and dining area that housed a kitchen centrally, enabling the gentle spilling out into adjacent common spaces. Hence the brief was fairly contained, with the only other requirements being a master bedroom with an ensuite, and a study which could double as a guest room on occasion, along with a separate bathroom. A garage was also required to house the clients’ range of outdoor recreation gear, as well as the Tesla power wall and electric car.