Govetts Leap Bach
Client brief
The brief for this project was a small house for two avid rock climbers from New Zealand, who were eager to minimise the impact of the build on the environment. This manifested through an all-electric, passive and environmentally sustainable design methods but also the curtailing of the footprint to a mere 81m2.
Response
Sitting at the edge of the bush, in the Blue Mountains, yet wedged between two occupied blocks, the site is thoroughly suburban in its size but also because of its proximity to the neighbours. Nevertheless, the bush fire risk was deemed as extreme, with the dwelling designed and detailed to meet BAL FZ (Bushfire Attack Level Flame Zone) requirements. The desire to preserve privacy between neighbours but also engage with the bush and create a sense of being immersed within it were key factors in the initial massing of the house. Towards this, there are two wings of the house that reach to the north to capture sunlight and promote natural daylighting within the house, and extend to the rear of the property towards the bush.
Driven by the client brief, but also our own commitment to environmental sustainability this was one of the first houses that we’ve taken that next step and designed with Passivhaus principles in mind. The outcome, while never intended to reach Passivhaus certification levels, is expected, through the thermal comfort facilitated through airtightness, insulation, optimal indoor air quality, reduced thermal-bridges, high performance windows and heat-recovery ventilation to deliver an extremely efficient and comfortable home. This project demonstrates that a highly sustainable approach doesn’t have to limit the possibility of a visually radical and contemporary architecture in extreme bushfire environments.
Key Features
– An airtightness rating of 2.0 ACH was achieved through the utilisation of the Proclima Intello wrap to interior studwork and ceiling frame.
– TBA Firefly BAL-FZ wall sarking, lines the external walls, behind cladding.
– The Windows are Paarhammer BAL-FZ rated timber windows and front door. The glass is a special fire rated double glazed Low-E with argon gas.
– The joinery throughout the house, including the wall lining and joinery carcasses are made using Plytech Green plywood which is FSC and PEFC chain of custody certified.
-A heat recovery ventilation system (HRV) from Stiebel Eltron, was fitted with a ‘smoke box’ filter on the external air intake vent. During bushfire events a smoke specific filter can be utalised making it one of the first homes in Australia to use this technology that will virtually eliminate smoke inside the home.
-A life cycle assessment determined the Global Warming Potential (GWP) of Govetts Leap Bach to be 13kg of CO2/m2/year over a 50 year lifespan, which is on par with the exemplar standards of Denmark, that require all new buildings to achieve a GWP of no greater than 12kg of CO2/m2/year.
– Benchtops and window sills are made from Paperock – a product Made from layered recycled paper and bonded with phenolic resin.
– Internal walls are constructed from Austral Masonry Australite concrete blocks, which have recycled content, require less mortar and are also physically lighter than traditional blocks, which translates into a lower carbon footprint in terms of their transportation.
– Thermal bridges were minimized with the inclusion of Foamglas blocks between the structural slab and concrete block walls to reduce the transmission of cold and heat travelling into the interior space.
– An Insulated Hanson Bronze concrete slab incorporates fly ash, slag, silica fume, recycled aggregate and uses recycled water during production. Compared to traditional concrete, Hanson Bronze saves around 67KG of embodied carbon per cubic metre.
– Hydronic underfloor heating in topping over insulation layer.
– Walls are painted with zero VOC paint from Ecolour.
– 10kL Rainwater & bushfire fighting storage tank.
– Stiebel Eltron instantaneous 3 phase hot water system which makes hot water only when required.
– 8 kw solar PV system with a 13.5 kwh Tesla Power wall battery system. When the PV output and electrical load were modelled in Passivhaus software, the house achieves carbon neutral status, year round.
