A Passive House is a building in which indoor air temperatures above the WHO recommend minimum of 18°C are maintained year round without the need for heating appliances. For indoor comfort however, 18°C are not sufficient; for a comfortable home, a minimum of 20°C is required. In a Passive House, the small amount of energy needed to lift the temperature profile accordingly can be supplied via the ventilation system.

That is right, neither radiators, nor wood or gas burners, nor heat pumps or air conditioners are needed to live in a comfortable, dry and well ventilated house. This is not a case of wishful thinking but rather of applied physics. All you need is a maximum heat load of 10W/m². 

Every new building can be a Passive House, the standard is not confined too residential dwellings. Personally I have been involved in the planning process of a Passive House office building, and a Passive House school. They all have great thermal comfort in common. 

Is this an experimental concept?

No. There are currently more than 30,000 Passive House buildings operating in the world (most of them operating with considerably more extreme outdoor temperatures, than you will find in New Zealand), with the oldest one up and running since 1991. The Passive House concept is proven both scientifically and empirically to work well.

Is a Passive House also a Zero Energy House?

No, it is not. You still need a minimal amount of external energy to provide a comfortable and healthy indoor climate in a Passive House, although in some regions in NZ that amount would be next to zero. You certainly can go the extra mile, and turn a Passive House into a Zero Energy House. But this very last part of the way is the most expensive. A Passive House tries to balance economy and ecology, and therefore stops short of the last meters. You can easily cover the remaining need for heating and cooling energy with renewables, though, but the therefore applied technology is mostly active. 

Why is it called Passive House?

A Passive House tries to provide a comfortable and healthy indoor climate without the need to use active heating or cooling appliances. It heats and cools itself. There are machines to facilitate this purpose, namely an efficient ventilation system (no air-conditioner!), but many experts consider a ventilation system a vital ingredient of a healthy and comfortable home anyway, so it is not specific to Passive Houses. Other than this, there is no machinery needed. A good ventilation system by the way is easier to operate than your average remote control.

Do I need to have a north facing site to build a Passive House?

No, there are plenty of examples where a Passive House works perfectly without being aligned ideally. It is a bit harder though, but definitely possible.

Do I need thermal mass?

No. Thermal mass is a supporting actor. Nice to have, but not a precondition.

Can I open the windows in a Passive House?

Sure you can! Only – you do not need to do it, if that is your choice. But you definitely can do it, if you want. It is up to you.

Are there specific shapes needed for a Passive House?

No. You might very well build a Passive House that looks like a 19^th century villa. You can have it look Tuscan style or state house, or just plain modern. They come in all sizes, too.

What about summer?

The good news: insulation works both ways on opaque components like walls and roof. The “solar” design you chose to catch the sun in winter however could be a mayor problem in summer. One more reason why you should not exaggerate window sizes, because thereby you also magnify summer heat load. But there is a solution: keep the sun out in summer simply by using movable shades, like shutters. Always put them on the outside of your windows. It would be nice to automate closing and opening in dependence of solar radiation, too. This can be done quite easily with a small photovoltaic sensor and solar driven motor. On the other hand, you might need the exercise of doing it yourself… The ventilation system can, in combination with a mostly passive ground heat exchanger, work as a dehumidifier and also cool down indoor air a bit. Again: a big step towards comfort with only a small amount of energy!

How do Passive Houses work?

They work by minimizing heat losses and maximizing passive heat gains. To minimize heat losses you first and foremost need lots of insulation (roughly 15 cm+, depending on location in NZ) . By insulation I mean materials with a thermal conductivity ≤ 0,1 W/(m K). This could be wool-, cotton- or polyester fleece, cellulose, glasswool, polystyrene, foam glass, fibreboards, straw bales or others – in other words: low density materials with many enclosed air cavities. Neither rammed earth, nor clay, nor loam, nor concrete would do, since all of those do not have noteworthy insulation values. 

All the windows, too, need to be very well insulated. And do not oversize them. Think of your home as a present: you need to wrap it all around neatly. And do not forget the corners! 

Next you need an airtight barrier interior of the insulation layer. This can be made of any material that is and stays airtight. Building papers, polyethylene foil, engineered timber boards, plaster etc..  Just do not forget joints and connections. They need to be airtight, too. Read more …

You need to ventilate your home. But you do not have to loose indoor warmth doing so. Heat recovery is the solution. It only works well in airtight houses, though. Read more …

Now that you have cut the losses, maximize the gains. Catch as much winter sun as possible – but avoid overheating all the same. Try to align the house as north facing as you can, and provide moveable shades on the outside of the building. You also receive gains from appliances and occupants. But it is not very wise to maximize gains here. In the case of appliances: you would not want to waste the energy you save on heating to run inefficient appliances (efficient appliances only generate minimum heat). And I do not reckon you want to subdue your families planning to heating purposes, either (more persons will yield more interior gains). Heating problems solved, think about warm water supply. You can easily get it without burning fossil fuel or fossil generated electricity. Solar water panels are readily available to do the job without sending monthly bills. There are systems operating in Europe, where solar panels are integrated with the heat recovery system. Even a clothes dryer can be part of the ensemble. So far these systems are not readily available here. Hopefully it will only be a matter of time. But even without the most sophisticated technology: it is very well possible to build a Passive House in New Zealand!