“It’s just a house,” says Glenn Murdoch, the design director of Theca Group. “There’s nothing special you can see. The only thing [visible] is that the windows and doors are different.
On the slope between the subtle and sprinkled projects of Passive House, Blackstone Apartments, an affordable 19-unit housing development in Portland, Maine, falls so far towards the subtle end that it falls completely off the chart. “We don’t discuss Passive House with the client,” says Jesse Thompson of Kaplan Thompson Architects. “Passive House was never a project goal, but the project should be able to meet PHIUS metrics. The property owner learned that the project was likely to meet the Passive House requirements only after final testing of the fan door.
“High-profile Passive House projects in their early stages are often launched with integrated teams, lots of fanfare, and extensive lists of consultants,” Thompson says. For many projects, however, that approach is not realistic. Kaplan Thompson Architects has gone further in its recent projects, exploring the question: How do we take Passive House’s strategies to integrate multi-family construction when the budget doesn’t allow for additional consultants or almost nothing else? Or when the owner perceives the Passive House as a luxury asset?
When working within a limited budget, the company strives to prioritise the most critical elements of the passive house, balancing improved ventilation, tightness and insulation to achieve the best possible building. For this project, Thompson pushed the team on waterproofing and ventilation while maintaining a low profile in terms of insulation specifications. “Our multi-family work has shown us the effectiveness of having at least 85% efficient ventilation,” he says, “which makes more than one foot of insulation. In addition, he adds, the developers have had decades of experience in reducing insulation to reduce project costs, so they are very skilled at it.
But those differences are important. All windows and doors have triple glazing. They are 90 millimeters thick, compared to the 60 mm of conventional double glazed doors and windows.
Triple glazing costs more, of course, but has significant advantages over heat control.
This house costs “fucking” to heat, says Murdoch. In winter, electricity bills are less than a month. In summer, electricity bills are nil, he says.
In part, the house does not need power from the grid because of the solar panels on the north side of the roof. In summer, they generate enough energy to run the house and send some electricity to the grid.
Achieving this level of energy efficiency costs 5 to 10 percent more than conventional construction, says Murdoch. Christchurch homeowners, who want to remain anonymous, spent about $675,000 building their home.
“It doesn’t cost more, you’re going to invest more,” says Murdoch with a certain ability to sell.
“It’s an important distinction…. everyone talks about the cost of capital and nobody talks about the running costs of operation.
Lower electricity bills have been estimated to offset rising mortgage costs month by month, leaving homeowners ahead, he says.
Energy efficient, comfortable and affordable houses
It is a passive house, a construction standard conceived in Europe that leads to a house that is “truly energy efficient, comfortable and affordable“, according to the Passipedia website.
“It’s a building performance standard, not a design guideline,” says Murdoch, who is an architectural designer.
“Passive House specifies a result…. and the underlying principle is that it provides a comfortable and healthy building. Energy efficiency is a secondary benefit,” he says.
Architects and engineers decide how the standard is achieved, although many passive houses in New Zealand have common elements, such as triple glazing and a demanding thermal envelope.
Passive houses are not zero-energy houses or off-grid houses. There is no composting toilet, although owners can have one if they wish. There is no heat sink or battery, although homeowners may have one as well. However, wood fires are difficult to include.
So far, 22 passive houses in New Zealand are listed on the Passive Haus website, 13 on the North Island and nine in the South. Others are under construction or not yet certified. And some owners chose not to certify.
The websites list nearly 4300 passive buildings around the world, including schools, fire stations, old people’s homes and factories.
As a general rule, they have to meet the standard comfort level of the Passive House of about 20 degrees Celsius 365 days a year. In summer, the building cannot be more than 25°C for more than 10 percent of the time occupied.
The winter standard is expressed as a mathematical formula that is difficult to display in print. But Murdoch estimates that it is about one-tenth the heat requirement for a typical Building Code compliant home.
In addition to triple glazing and photovoltaics, this is achieved through the thermal enclosure. It consists of three layers – a hermetic layer, an insulating layer and a wind and weatherproof layer. In the colder climates of New Zealand, the insulation layer is usually thicker than in the warmer parts of the country.
These layers have to be installed to exacting standards to minimize the number of “air changes per hour” to less than 0.6 per hour at 50 Pascal, or in other words, on a fairly windy day.
In conventional homes, drafts and heat loss are more common around windows and doors, and from corners, says Murdoch.
These demanding installation standards mostly resolve these leaks and can be tested with a fan door test, a technical measure of air tightness. But the design of the house also helps, so the Christchurch house has a simple shape that reduces the number of corners.
Ali Wilkinson and his family have a more complicated passive house. Their 100-year-old villa in St Albans, Christchurch, was not profitable to repair after the earthquakes and they wanted a contemporary house that looked like a villa. Only after completing the 250m2 design was it decided to turn it into a passive house.
The result cost 5 to 10 percent more than the conventional house and they had to increase insurance money to meet the standard, he says.
But after living in a damaged old villa, the family realizes how quiet and tranquil the house is. As for the temperature, “I’m barefoot all the time,” she says. Her hay fever symptoms have been reduced.
When temperatures in the city rose above 30 degrees Celsius last summer, the Wilkinson house was 6 to 8 degrees colder than the neighbors, he says. They have credit with their electricity provider after the summer.
Even in extreme heat conditions, Passive Home designers must consider water vapor from indoor and outdoor sources, such as kitchens and bathrooms. The Passive House standard doesn’t specify how these problems should be addressed, but a common solution is a ventilation system that extracts steam from the kitchen and bathrooms and expels it.
In conventional homes, steam is removed with kitchen and bathroom exhaust fans and through windows. “The evidence is clear, that doesn’t work,” says Murdoch. “The evidence says we have to ventilate mechanically.”
Ingeniously, fans often include heat exchange technology that captures heat from the kitchen and bathrooms and recirculates it throughout the house.
This helps achieve the goal of “warmth and comfort,” while only two small fans are needed, says Murdoch. These fans have come down in price in recent years and now cost about $10,000 installed. Filters in the unit remove contaminants.
The biggest energy leak from Christchurch’s first home is water heating. In other circumstances, solar energy could have been used, but Murdoch ran out of space on the roof and installed a heat pump.
Christchurch’s first home also reached a higher level, called Passive House Plus, which stipulates the amount of energy to be created at the site.
Murdoch, who had financial difficulties with a former company that built passive houses and now works for Theca, points out that the design includes shutters in the windows facing north. These shade the windows on clear days and help control heat gain.
In conventional homes, curtains are often closed to achieve the same effect. But once the heat passes through the glass, it’s too late, says Murdoch. The house won’t be warm and comfortable.