11.7 Surrey Hills, Victoria

This extensive renovation of a 1930s duplex in Surrey Hills, Melbourne, incorporates the latest technology in solar efficient design, water collection, greywater re-use, and photovoltaic grid-interactive power systems. It also uses forest friendly timber products and low toxicity finishes.

The owners, a young couple, wanted to renovate their 1930’s brick duplex. The existing home was a maze of small pokey rooms.

Their brief called for the existing home to be upgraded to a solar efficient 2-bedroom home with large living areas, two separate studies and two bathrooms. They were keen to incorporate the latest technologies in sustainable home design.

The climate is cool temperate. The prevailing winds come from the southwest in winter and from the northwest in summer. The diurnal (day/ night) temperature range normally exceeds 8°C. [See: 4.2 Design for Climate] The site is a long urban block, 48 x 10m wide, running east-west. Northerly access was limited by the presence of the neighbouring half of the duplex, situated directly north and sharing a party wall. The neighbours’ proposed extension also had to be taken into account. [See: 2.2 Choosing a Site; 4.3 Orientation]

DESIGN SOLUTIONS

General planning

The existing home was partly demolished and re-planned. The front living room was converted to a master bedroom with ensuite attached, and the rear of the building was removed and rebuilt. Only two rooms remained intact by the completion of the project.

Maintaining the streetscape and the connection to the neighbouring duplex was seen as important by the owners. This was achieved by leaving the street facade of the house intact to match the neighbouring duplex and to fit in with the character of the street. [See: 2.3 Streetscape]

The extension was built with a suspended concrete slab for thermal mass and an AAC blockwork party wall for its excellent fire rating and good sound insulation properties. The pitch of the north-facing roof was designed to accommodate solar panels and a solar hot water service. [See: 6.7 Photovoltaic Systems]

Courtyards were located to the north of the building to maximise solar gain, with an extensive area of double glazing in the roof over the dining/ living area. [See: Passive Solar Heating]

Cladding

External walls are a combination of rendered fibre cement sheet and AAC blockwork. Both products were chosen on an environmentally preferred basis for their low embodied energy and more sustainable manufacturing processes. [See: 5.1 Material Use] Boundary walls are AAC (autoclaved, aerated concrete) blockwork. The fire rating and insulating properties of this material made it an ideal choice for a boundary wall.

Thermal mass and insulation

A new suspended concrete floor slab at the rear of the house and the brick walls which have been retained at the front of the house provide the majority of the thermal mass required to even out day/night temperature variations. [See: 4.9 Thermal Mass; 5.12 Concrete Slab Floors]

Concrete slab insulation is provided by 50mm thick RMAX L grade foam insulation with an R-value (insulating value) of at least R1.0. This insulation was placed on the underside of the entire suspended slab. [See: 4.7 Insulation]

AAC walls in the dining area provide reasonable thermal insulation (R1.5 for 200mm thickness) due to the trapped air bubbles within the blocks. They also contribute moderately to the thermal mass of the structure due to the masonry component. [See: 5.5 Construction Systems]

Wool/ polyester bulk insulation batts were installed in the walls and ceiling. The R-value of the batts was R1.5 to walls and R3.0 to ceiling. ‘Air-cell’ (an innovative insulation product that combines the benefits of reflective and bulk insulation by trapping bubbles of still air inside reflective foil) was used in addition to bulk insulation in the roof. This increases the total summer roof R-value by around R2.2 and provides a sarking layer.