Studio style

Architects Uta and David Green’s experimental studio in South Hobart is complete, and helping to ease the city’s housing crisis.

On the slopes of kunyanyi/Mt Wellington in South Hobart, with tranquil forest views to the north and a creek burbling at its feet, sits a diminutive wedge-shaped studio. A secondary dwelling on the property of architects Uta and David Green, it was built as the new office of their practice, Green Design Architects.

As is often the way when designers create something for themselves, it was a testing ground for ideas and materials the couple wanted to try out: “As architects, when we design our own place, we get to play,” says Uta. In this case, they set out to create the most sustainable building they could, including minimising the footprint, designing with Passive House principles in mind, and carefully considering the embodied energy in the materials used. Uta documented the design process in an ‘Experts explore’ article in Sanctuary 56, back in 2021. Towards the end of that year and into 2022, hit by Covid lockdowns, material shortages and price rises, the studio was completed.

The unusual shape of the 60-square-metre building (42 square metres for the studio and 18 square metres of deck) is because the ideal building site – the part of the block with the lowest bushfire attack level (BAL) – is squeezed between an easement and a thoroughfare. “Although it’s on our property, we wanted to retain the track that provides fire truck access to the rear of the cohousing community next door,” explains Uta. Most of the floor space is taken up by the main room, which features large triple-glazed doors opening onto a sunny deck to the north. At its eastern end, the deck is a little wider and has a built-in bench seat. Still sheltered by the walls of the building, this space allows for outdoor living on Hobart’s warmer days, and offers the best view of the mountain. In the southern point of the triangle, tucked underneath a loft, is a compact kitchen and a bathroom.

The construction is lightweight: timber framing clad with fibre cement sheet, and a suspended timber floor. During the design process, David and Uta worked closely with energy assessor Rebecca Boyle to test the impact of different wall and floor construction options on the overall energy rating of the building (see the Sanctuary 56 article for more detail). A variety of wall frame depths, insulation levels, and innovative ways to introduce thermal mass into a non-concrete floor were assessed. “We were trying to work out what was easiest and most practical to build, that still had a decent Star rating,” explains David.

Because the building is so small, and Passive House standard harder to achieve in this climate, the walls needed to be thicker than the standard 90-millimetre frame. They opted for different combinations of 70, 90 and 140-millimetre layers on different walls, including thermal mass in the form of water-filled containers within some walls.

The thermal mass in the walls partly makes up for one idea that they didn’t get to include. Having modelled the inclusion of a 50-millimetre layer of sand under the timber floor and found that it would give a Star rating similar to an insulated concrete slab, they were all set to do that, but it was vetoed by their builder: “He didn’t want to get sand into his power tools!” recalls Uta. “On paper, it’s really easy to draw 50 millimetres of sand, but the practicalities are different.”

Although they tested the design using the Passive House software, Uta and David were not originally planning to pursue full Passive House airtightness, as they were concerned about the noise of a mechanical ventilation system with heat recovery (MVHR) in such a small space. Instead, they planned to experiment with low-tech ‘trickle vents’ they developed when designing bushwalkers’ huts for the Overland Track in Tasmania’s wilderness. However, one pandemic-related material substitution “required a lot of extra bracing on the outside of the wall, leading to an increased risk of condensation and mould in those places,” says Uta. “We ended up installing an internal membrane to combat that, and going full Passive House after all.” They are happy to report that despite their fears, the decentralised MVHR is whisper-quiet.

The finished studio is a delight: light, bright, cosy and quiet. “It’s a very beautiful space, and that’s important,” says Uta. “We might forget about the ambient feel of a place if we just talk about the performance, but it’s the feel that really makes us happy.” David agrees. “Passive Houses can sometimes be rather unattractive: like a machine, rather than designed for beauty and for the occupants. This one does both. The space feels wonderful, and it hugs you on grey days.”

It’s lucky that the couple’s approach to designing sustainable buildings includes flexibility for future uses, meaning that the studio was intended to be able to function as a small self-contained home after its life as an office. “Little did we know that the Covid years would bring a severe housing crisis to Hobart,” Uta says. “We did briefly use the studio as our practice office, but now we are providing it for someone to live in, until (hopefully) the housing situation relaxes in the next few years.”