A Dunedin couple have built a new home with no heating. What were they thinking? Kim Dungey reports.
It's a cool, rainy Monday but John Crump is walking around home in his shirtsleeves.
The temperature outside hovers around 9degC. The temperature inside is about 22degC. In every room, every day of the year.
Yet there is no fireplace and no central heating.
''I call it the anti-Dunedin house,'' Mr Crump says.
''It's light and it's warm.''
The home is the first in Dunedin to be certified under the international ''passivhaus'' standard which is designed to maintain an indoor temperature of 20-22degC while reducing heating costs by about 90% over a code minimum build.
The standard, which can apply to all buildings, not only houses, was developed in Germany in the early 1990s while Mr Crump was living in a ''freezing'' Dunedin flat and studying medicine.
When he and wife Jen moved back to the city five years ago, they resolved to find a warm home. It proved a challenge.
''We looked at a lot of real estate, before deciding to go for a derelict place and starting again,'' says Mrs Crump, a teacher who hails from Vancouver.
''The problem around Dunedin is that a lot of houses that are considered derelict are still able to be rented out to students.''
After demolishing a Stuart St property with mould and rotten floorboards, the couple commissioned architect Tim Ross, of Architype Ltd, to design them a child-friendly home that made the most of the views, had outdoor space and would not look out of place among its traditional neighbours.
Overlooking Otago Harbour, the house has public spaces at the front and private ones behind. The two living areas and four bedrooms are organised around a sheltered, sunny outdoor space to the north of the site. The stacking volumes and reinstated bluestone wall take cues from the historical homes nearby.
But it's what you don't see that makes this home different. It has very high levels of insulation. The building fabric is extremely airtight. Triple glazing keeps the heat in. And fresh, filtered air is delivered to every room, thanks to a ventilation system that also transfers most of the warmth from the outgoing air to the incoming air, resulting in low energy losses.
As in a passive solar home (that may have concrete floors and large north-facing windows), the house uses free heat from the sun. But it also traps the heat generated within: the physical body heat of the occupants and the warmth produced when they use household appliances, take a shower, use the computer or watch TV.
Passive House Institute NZ treasurer Guy Shaw says an entire passive house could be heated with a bathroom fan heater or the equivalent of a hairdrier: ''Most of the year, you don't need heat and when you do, it's not much at all.''
The Crumps are yet to spend a winter in their home, but Mr Ross, who has since designed 19 passive houses for a co-housing project to be built on the site of the former High Street School, estimates that on the coldest, windiest night, there will be a need for 2kW of heating. This could come from an oil column heater, he says.
''Or they could put a roast on or have some friends around.''
Space-heating requirements have been calculated at 14kWh per square metre per year.
''This means each year each square metre of floor area will require a mere 14 kilowatt hours of energy to maintain an indoor air temp of 20-22degC. To put this in perspective, a house built to the NZ building code minimums would require around 150kWh per square metre per year and even then, there would be problems with humidity, condensation, mould and draughts.''
The German standard does not dictate any particular construction system or materials but sets 15kW per square metre per year as the maximum amount of heating or cooling that can be used to maintain comfort year-round, then leaves owners to work out how to achieve it. Avoiding overheating in summer is crucial, so the Crump house has few west-facing windows and an overhang protects the large glass sliding doors in the living area.
As with the 12 other certified houses in New Zealand, key components were imported from Europe. These included the high-performance windows, the ventilation system and the structural insulated panels used for the exterior walls. The panels, which have polyurethane insulation sandwiched between oriented strand board, were lifted in by crane fully assembled.
Inside, plasterboard walls provide a cavity through which to run power and plumbing and avoid unnecessary penetrations of the thermal envelope. A condensing clothes drier and a recirculating rangehood were chosen for the same reason.
Passive houses reduce the heat lost through the building fabric by insulating the walls, roof and floors in a continuous layer and minimising the thermal bridges often found at junctions between elements, Mr Ross says, drawing an analogy between constantly topping up the heat in a draughty home and filling up a leaky container: ''You can have a bucket and just accept the holes in it and constantly fill it up with water. Or you can plug the holes and keep the water in there.''
Building the world's southern-most passive house was not without its challenges. The design took two years and the construction 18 months, partly due to the big basement and external bluestone walls. A simpler, more compact design would have required less insulation because a larger thermal envelope transmits more heat per usable area and a complex shape involves more junctions. The documentation required was also extremely detailed.
Using a spreadsheet modelling tool allowed Mr Ross to optimise the windows and insulation, modify the design as he went and have certainty around the final thermal performance. There were also two tests to measure the amount of air leakage from the 224sq m L-shaped building. The results can be significantly affected by nail holes or gaps around plumbing and windows.
The Crumps say the glazing, thermal modelling and certification added about 10% to the home's construction costs, but reduced running expenses mean it will pay for itself relatively quickly. Their power bills used to be $200 in summer and up to $600 in winter. Now they are $60-$70.
Michael Sly, whose home near Arrowtown has also been designed with no heating or cooling, says costs will reduce as more components are made in New Zealand. Last year he and his business partners set up a Cromwell factory to manufacture structural insulated building panels, and recently the 135mm-thick larch window frames made by Mosgiel firm ThermaDura became the first building product in the southern hemisphere to be certified for passive house projects. Certified materials are not mandatory, but owners using them know the manufacturers' performance claims have been checked.
Before moving into their 150sqm home 15 months ago, Mr Sly and partner Jodie Lynes spent $11,000 a year on energy and petrol. Now, with no heating and a hybrid vehicle that is recharged partly from solar panels on the home's roof, those costs are about $1500.
Being warm without any heating system, even when outdoor temperatures plummet to -7degC at night and only 2 or 3degC during the day, is a ''surreal feeling'', says Mr Sly, a director of design and construction company Climate House.
''In a passive house, you don't have to do anything. You don't worry about drawing curtains or getting the fire ready. You literally walk in and it's 20 to 22 degrees through the entire home. There are no cold spots and no draughts.''
The concept is so foreign to most people that he once drew an ''undie-o-meter'' showing how many days he felt comfortable walking around in his underwear. In his old house, he always reached for something to put on as he got out of bed.
Critics of passive houses say the German model is not suited to all climates and its sophisticated, often expensive, systems are an over-the-top approach for New Zealand. Mr Sly says local climate data is used for calculations, so a passive house in Nelson, for example, would need less insulation than one in Queenstown and only double rather than triple glazing.
Another ''misconception'', those interviewed for this story say, is that occupants can't have their windows open.
''You can leave the windows and doors open whenever you like,'' Mr Ross says, ''but in the middle of winter you don't have to leave the windows open to get fresh air into the building.''
The men say New Zealand lags behind most other developed countries that have raised their building standards in the past decade and experienced economic and health benefits.
Mr Shaw says it is ironic that Nasa astronauts are able to work in a ''shirt-sleeve environment'' in space, but New Zealanders struggle to achieve it in their houses.
''The whole point of doing this is the concept of comfort, that generally, as New Zealanders, we have no idea exists,'' Mr Sly says.
''It's like trying to explain what snow looks like to someone who's never seen snow.''
Many of the houses his firm builds are not full passive houses but are low energy: ''It's not this or nothing. You just try your best.''
Building costs have increased, so people should consider building smaller homes, too: ''The rest of the world is building three-bedroom, 120 to 140sq m houses. Here we have this 200sq m-plus philosophy. If you [do away] with the [extra] 60sq m, you can build a much more beautiful, high-performance home and have lower living costs.''
Back at their house, the Crumps are listing some of their favourite features. These include the sweeping views and the study where Mr Crump, co-director of the Centre for International Health at the University of Otago, can work across time zones without disturbing his four young sons. But it's the comfort factor they really appreciate.
''I can feel the air moving and it's fresh air, not stale, musty air,'' Mrs Crump says.
''The only time we put on jerseys is when we go outside. The only condensation we occasionally see is on the outside [of the windows].''
''The kids used to stand on a chair, just to get dressed,'' she says, demonstrating how they would stretch upwards to get close to the wall-mounted heatpump in their old house.
''Now they don't even think about that.''
''People who come at night, [notice] we don't have to close curtains to keep heat in the house. And they're surprised there's not a heater on.''
- The Crumps are monitoring indoor and outdoor temperatures for 12 months. To see the results, go to https://tinyurl.com/hj9lt79. Different time periods can be selected at the bottom.
The details
• Walls were constructed using 140mm thick ''structural insulated panels'', which provide insulation values three times higher than current building code minimums
• Well-insulated timber window frames and high-performance triple glazing drastically reduce heat losses through the windows and doors
A solid layer of insulation under the timber flooring on the ground floor creates a continuous ''thermal bridge free'' connection to the wall construction
• The roofs have timber trusses with 300mm of fibreglass batts. An airtight membrane under the bottom chord of the trusses creates a draught-free roof assembly
• Every junction in the external envelope has been designed to be airtight, eliminating draughts and air infiltration from outside (the thermal envelope does not include the garage)
• A mechanical ventilation system draws stale, humid air from the kitchen and bathrooms and supplies fresh, pre-warmed air to the bedrooms and living areas. The system transfers heat from the stale outgoing air to the fresh incoming air, resulting in low energy losses
• Hot water comes from an air-sourced heat pump and there is a drying cupboard for passive, low-cost drying of clothes using the home's ventilation system
• The home also has LED lighting and energy-efficient appliances
More information
• For more information on passive housing, visit www.phinz.org.nz
