Ultimate guide to a Passive house
Passive Houses (known as Passivhaus in most of mainland Europe) are homes designed to combine ultra-low energy consumption with consistently good air quality.
They are built to a rigorous voluntary standard, with superinsulation, low-volume heat recovery ventilation systems and tightly controlled rates of air infiltration, which combine to make sure the building’s carbon footprint is as small as possible.
By achieving Passivhaus standards, a building can manage without conventional heating systems, although most Passivhaus structures do have some kind of minimal heating system to boost temperature levels.
Who first thought of Passive Houses?
The idea of a Passivhaus began with a conversation in 1988 between a Swedish academic, Bo Adamson, and Dr Wolfgang Feist of the German Institute for Housing and the Environment. They developed their concept through a series of research projects, and the first experimental Passivhaus homes were built in 1990 in Darmstadt, about 27 miles south of Frankfurt in south-west Germany. The modern version of the Passivhaus developed from these prototypes.
In 1996 Dr Feist founded the Passivhaus Institute, a research institute dedicated to developing the Passivhaus and encouraging countries around the world to adopt its standards and technology. In 2001 Passivhaus buildings began appearing in other European countries, but the majority of Passivhaus buildings (around 25,000 in 2010) are still in the German-speaking countries and Scandinavia.
The first Passivhaus-certified structures in the UK were built in Machynlleth, in Wales. They include The Stag Centre, a Passivhaus office, and Y Foel, a private dwelling. Other Passivhaus buildings around the world include schools, kindergartens and a supermarket.
Passive solar home design
There’s even a Passivhaus houseboat in the Netherlands. It doesn’t need any dock connectors for energy or water; it gets energy from solar hot water collectors and processes water through a built-in water treatment system. It also has a heat recovery ventilation system, EPS insulation, and IKEA furnishings.
What are the advantages of living in a Passivhaus?
An officially certified Passivhaus home or workplace, designed and built to Passivhaus standards, can provide:
- Lower energy bills and protection from fuel price rises.
- Warm, snug rooms without any draughts or cold spots in winter, and cooler rooms in summer.
- Cleaner, healthier air quality inside.
- Low maintenance costs.
- Less technology to go wrong, so there are fewer heating emergencies and expensive repairs.
- Peace and quiet when the windows are shut.
- More wall space, as you don’t need any radiators – giving you more choice of where to place pictures, pianos or sofas.
Some Passivhaus advocates also claim that you get more floor space because of the lack of radiators. This isn’t strictly true, as Passivhaus walls tend to be thicker to provide more insulation, which can actually reduce the floor space.
How energy efficient is a Passivhaus?
This table compares a superinsulated Passivhaus with a modern home and a heat-leaking Victorian house.
As you can see:
- A Passivhaus needs just 15 kWh of heating energy per square metre net floor surface per year (15 kWh/m2a). Assuming it’s an average-sized UK home, that’s the equivalent of around £50 worth of gas per year.
- A draughty gas-heated Victorian villa (the same size as the houses above) would use 300 kWh/m2a and spend £1,000 a year.
Passivhaus standards require that a building does not exceed this 15 kWh/m2a standard – if it does, it can’t be classified as a Passivhaus.
What is superinsulation?
Superinsulation is simply a way of building that produces much greater levels of insulation and airtightness than usual, so that the cost of heating its internal spaces is lower than the cost of its hot water.
There are no set parameters that define superinsulation, but a superinsulated building would probably be:
- Insulated to a U-value of 0.15 watts per square meter kelvin in the walls and 0.1 in the roof. The U-value is the rate at which heat passes through insulation; it should be no more than 0.30 watts per square metre kelvin – in fact, the lower the better.
- Built so that the insulation continues without a break wherever walls meet the roof, foundation or other walls.
- Completely airtight, particularly around windows and doors.
- Supplied with a heat recovery ventilation system to provide fresh air.
- Fitted with relatively small windows on all sides. (Although Y Foel, one of the passive buildings in Wales, has very attractive large windows.)
- Heated by a smaller system than usual, such as a single backup heater.
A superinsulated house should have very low heating needs and should mainly be heated by integral sources, such as the waste heat produced by lighting and electrical appliances or the body heat of residents, pets and visitors. According to Wikipedia, each person can emit heat equal to an average of 100 watts of radiated thermal energy.
The extra cost of building a home with superinsulation can be balanced out by the fact that there’s no need to install a central heating system.
The first superinsulated houses, which predated the Passivhaus movement, came in standard shapes with stud walls, but nowadays they take all kinds of shapes (e.g. earth-sheltered, earthship) and materials (including concrete, straw bales or insulated panels). Any regular watchers of aspirational design-and-build TV programmes will have seen all of these.
Do Passive Houses have special windows?
To retain as much heat as possible, Passivhaus windows are made of triple-pane insulated glazing, and the gaps between the glass panes are sealed and filled with argon or krypton gas. Their technology also includes a ‘low-emissivity’ coating, ‘warm edge’ glass spacers and specially developed thermally broken window frames.
Do they need special furniture and fittings?
If you want your superinsulated home to comply fully with Passivhaus specifications, you’ll need to select furniture and interior finishes carefully to make sure you’re minimising air pollution indoors. That means checking for volatile organic compounds (VOCs) when choosing paint, for example. If you can’t avoid all VOCs, you’ll need to add plants or even a water feature to your interior decor, and also open the windows briefly at intervals.
Do all Passive Houses look the same?
Not at all. Passive Houses come in a wide variety of styles and layouts.
They can be built from either dense or lightweight materials, but they always need a certain amount of internal thermal mass to reduce heat in summer, maintain stable temperatures in winter and prevent overheating at other times.
You can choose the colour of the external walls, but they need to be designed to reflect or absorb heat, depending on the average temperature where you live, and this can limit the choice of colours.
Is it true you can’t open the windows in a Passivhaus?
No, it’s not true. In summer, a Passivhaus needs to have openable windows, to release any heat that’s accumulated during the day. In winter, it’s still possible to open the windows but, depending on where the house is sited, the air might feel fresher inside than out, so residents prefer to keep them shut.
Keeping the windows open all night, every night, can reduce the internal temperature slightly and add a minimal amount to a Passive House’s energy use.