As winter approaches, the young and the elderly are benefiting from Dunedin rentals designed to passive house standards. Kim Dungey reports.
The picture propped on top of Terry Collard’s heater says it all.
The appliance hasn’t been switched on since the 79-year-old moved into the Dunedin City Council’s School St units last July.
The previous council flats on the site and the energy-efficient one he now lives in are like chalk and cheese, he says.
"For one, my power bills have gone from $70 a fortnight to $15, because I haven’t used the heater at all."
The council complex is the country’s first social housing project, and new student apartments in Leith St the first developer-led project, to be certified to the passive house standard. They are also the second and third certified passive house multi-unit projects in New Zealand after the the Toiora co-housing development in Dunedin’s High St.
Both were designed by Architype, which is also working on passive housing as a pilot for one of the country’s largest group home builders, Fletcher Living in Auckland.
Architect and certified passive house designer Tim Ross describes a passive house building as one where the building envelope protects the occupants from the elements and maintains a comfortable indoor environment with minimal energy input.
"It’s great for students ... but if you look towards older people, who are more home-based, the benefits are even greater. They’re in the environment much longer so the cost savings are magnified even more."
He believes passive houses are the way of the future, given increasing concerns about energy security and climate change.
Kainga Ora is building its first passive house pilot project in Auckland. In Scotland, authorities plan to mandate passive housing for all social housing projects by next year.
In both Dunedin developments the units have been designed to be draught-proof, with a centralised hot-water heat pump system providing reticulated hot water for about a quarter of the usual cost and mechanical heat-recovery ventilation systems constantly providing fresh filtered air.
The ventilation systems extract moisture but also recover almost all the heat from the outgoing air. So even when the air outside is freezing, incoming air is heated by the outgoing air to 18degC. More heat is generated by the occupants themselves, appliances and cooking.
This means the units should remain at 20degC to 22degC with next to no additional heating. However, a small electric panel heater in each unit can be switched on in the event of cold winter nights or consecutive cold, cloudy days.
Triple glazing lessens heat loss and reduces noise transmission, the latter taking on more significance in a busy student area.
The developer behind the Leith St complex, where power is included in the rent, had already built student apartments with mechanical heat-recovery ventilation but struggled with them being stuffy. Modelling them using the passive house planning package meant that was not a problem, Ross says.
Co-ordinating the ventilation units for all 19 apartments and completing the build for a "reasonably standard" per square metre rate were challenges. However, using cross-laminated timber solved several issues.
While concrete and steel created moisture and cold spots, timber helped reduce thermal bridges and made it easier to achieve the passive house standard. The prefabricated cross-laminated timber reduced construction time, had an excellent fire rating and was lighter so foundations did not have to be as heavy. Having very little steel in the building also made it a low-carbon construction.
The sharing of walls means the building is inherently energy-efficient anyway, with the middle units losing heat only through the front and back walls.
When it came to the council units, the brief was to provide healthy, comfortable and energy-efficient accommodation for the tenants.
DCC property services group manager Anna Nilsen says sensors are monitoring environmental conditions in the units and the results will help inform future plans for council housing.
At this stage, there are no plans to build more passive housing or to retrofit existing units to passive house standards. However, work is under way to upgrade the heating and insulation at some community housing sites. The Palmyra complex in Carroll St has already benefited from this, gaining higher grades of insulation, heat pumps and thermally broken double-glazed windows.
The council has committed to investing $20 million in community housing over 10 years.
Mr Collard, who was the first tenant to move into the School St complex, appreciates the warmth, sense of security, level-entry shower and the fact triple glazing makes the units quiet inside.
The wider doors mean he can "put on quite a bit of weight", he jokes, but are also good for moving things in and out — he plays the piano, guitar and trumpet but the latter "is a bit loud, even for here".
Rents at the complex have increased to $185 per week (including hot water) because the nine units that were demolished were all bedsits and the new ones each have a separate bedroom.
But the reduced power bills mean "it probably comes to about the same outlay, for a much better situation", the retired electrician says, and building more council units to the passive house standard would be a "great idea".
"The problem is cost, I suppose. But I think once you built the place, the maintenance is going to be quite small because they’re beautifully built."
DCC community housing
- Ten one-bedroom units.
- Cost: $2.2 million.
- Walls constructed using structural insulated panels, which have high insulation values and minimise draughts.
- The homes are organised around a central green space. On the other side, each unit has its own small deck.
- The entire site has level thresholds between inside and outside. All doors are wide enough to accommodate wheelchairs and all bathrooms are fully accessible.
- Each unit has a parking spot for a mobility scooter by the back door. These spaces have power points for charging.
Leith St student apartments
- Three-storey complex, comprising 19 (mainly one-bedroom) units.
- Built from cross-laminated timber.
- Each unit has a north-facing deck or patio for outdoor space. The decks provides shading for the units below, preventing them overheating.
