Building Design
Energy and Greenhouse Emissions
Design response
The building is situated on the highest point of the property to take advantage of the spectacular views over the Clematis Valley to the north and to facilitate vehicular and services access from the existing road. The designers chose to orient the building to approximately 15 degrees west of north to follow the line of the contours and to avoid overshadowing by the large adjacent trees to the north-east. The building form of two stories is set into a bermed wall on the south side of the dwelling and opens out to large areas of glazing to the north.
All habitable rooms are located on the north of the dwelling to receive optimum solar access. The ground floor steps up the contours of the slope from the west to the east with with a floor difference of 0.75m. All living areas are located on the ground floor with bedrooms on the upper floor set back from the line of the ground floor to form a north facing deck. Service areas and carport are located on the south side of the dwelling and the entrance is located on the sheltered east side. An existing stand of trees has been retained to the south and west of the dwelling to act as a windbreak.
Energy and greenhouse emissions
Natural daylight is maximised in the building with all habitable rooms oriented to the north. The design incorporated adjustable shading devices throughout the ground floor living areas to allow for flexibility in controlling solar access in an unpredictable climate. The meals area is shaded with a pergola fitted with adjustable shade sails and the remaining north and west facing windows are fitted with parallel arm shading devices. At the time of writing these were yet to be installed, however the owners reported that the house still remained quite cool in summer. Upper floor bedroom windows are shaded with fixed eaves that are sized to admit the winter sun and exclude summer solar access.
The main bedroom is also fitted with a retractable vertical blind of a porous material to allow breezes and limited light to penetrate the room. In addition to the fixed eaves, the spa area is fitted with Azurlite, a heat restricting glass with a shading coefficient of 0.66 and visible light transmittance of 77%. While this is insufficient to prevent some unwanted heat gain in the summer months, the spa can be closed off to the rest of the house and vented through the door opening onto the balcony to the west and windows to the north east.
In a cool temperate climate, the main energy efficiency strategies were to provide an insulated envelope with internal thermal mass and to allow maximum solar gain in winter. The entire building envelope is insulated with R1.5 wool / polyester batts and Tyvek wrap in the walls and R3.0 loose fill wool insulation and sisalation / polyester blanket in the roof space. Slab edge insulation of R1.0 is also provided and all windows and doors are fitted with draught proofing. The windows are double-glazed, with all areas of glass on the ground floor fitted with low-E glass to give the equivalent performance of triple glazing.
Window frames are timber to minimise heat transfer losses through the frame. Large areas of glazing to the north admit the winter sun which is stored in the thermal mass of the ground floor slab and earth bermed wall to the south of the dwelling. This thermal mass also modulates the internal temperature in summer acting as a heat sink. The wine cellar is located in the south bermed wall section so that fairly even cool temperatures are maintained throughout the year. Nighttime cooling of the thermal mass is achieved through admitting the the cool summer night breezes from the south.
Cool summer breezes from the south-west are funnelled by the western south bermed wall and then admitted to the dwelling through small casement windows in the south wall which open in the direction of the breezes. Cool air passes through the living area and out through the glazed doors to the north of the living and meals area. The eastern side of the dwelling is also ventilated through southern casement windows, but due to the smaller areas of glazing, does not require the same level of ventilation. Stack effect ventilation is also encouraged in summer through the openable roof level windows above the staircase. The upper floor is ventilated in a similar manner with the addition of roof ventilator to supplement ventilation rates.
Auxiliary heating is provided by means of a Rinnai 4 and 1/2 star rated gas wall heater and open fireplace in the living room. The location of the auxiliary heating at the lower level of the ground floor allows heat from this area to migrate to the mezzanine area and then up the staircase to heat the upper floor. Additional off-peak electric floor coils are provided in the slab of the meals, kitchen and rumpus area. These are sized only to take the chill off the slab on cold winter nights rather than as a means of providing space heating.
No auxiliary heating is included on the upper floor and no auxiliary cooling is employed throughout the entire residence. The hot water system is an Aquamax 200 gas 5 star storage unit. The intention was to originally install a solar hot water unit, however it was found that this was cost prohibitive due to the inclusion of the spa. The designers have also specified low-energy appliances and efficient dichroic and compact fluorescent light globes throughout the dwelling.
Building materials have been selected to reduce embodied energy and to provide a highly durable finish. Most walls are constructed in aerated concrete block, a material that has approximately half the embodied energy of standard brickwork and finished with "The Paint", a highly durable exterior finish with a guaranteed service life of more than 20 years. Other materials used in the construction such as pine framing, recycled timber and cement sheet cladding were also chosen for their low embodied energy.
The building is designed to collect water from the roof to be fed into two lage water tanks, sufficient to provide all the water requirements for the property. At the time of writing however, these tanks have yet to be installed. All grey and black water from the dwelling is recycled in a Biocycle integrated waste management system for use on the lawn. Other garden areas have been designed with xeriscape plants to reduce water requirements. Appliances such as the Dishlex global 400 dishwasher and AAA rated showerheads and taps have also been selected for their low water usage.
The location of the dwelling in close proximity to the road and the design of the stepped ground floor slab along the contours of the site minimises the extent of excavation work required. Soil from the excavation work has been utilised to form the earth bermed wall to the south of the dwelling. Waste from off-cuts of the AAC and concrete blocks were also utilised in the bermed wall to provide adequate agee drainage. All timber materials in the dwelling have been selected from sustainable managed sources including the plantation pine framing and plywood flooring and the cedar window frames from suitably managed forests in Canada.