What is a passive house?

I intend over the next few weeks to explain all the main elements of passive house, from triple glazed windows, through heat recovery ventilation, airtightness and so forth. I would like firstly to explain what exactly a passive house is, however, so here goes.
Firstly, I need to clarify that the term passive house is perhaps a little misleading because you might have the wrong impression that it concerns only ‘houses’, but that couldn’t be further from the truth. I have visited a range of passive house projects across Europe, including passive house schools, passive house offices, passive house community centres, passive house churches and, believe it or not, even a passive house fire station. So, you can build pretty much anything to the ‘passive house standard’ (including a passive house house, by the way!). 

The next common urban myth about passive houses is that you have to follow a very strict design style in order to achieve the required standard. Week in week out we receive planning permissions drawings from people who want to test their house design to see if it can achieve the passive house standard. We’ve seen all sorts of shapes, sizes and orientations and the vast majority of them, with enough insulation, high quality glazing and good airtightness can pretty easily achieve the required standard. So, the passive house standard is not as limiting as many people assume in terms of building design.

Next, I need to emphasise that the passive house is not magic. You’ll read from time to time that passive houses are buildings that don’t need heating, but that is simply not true. All buildings in a climate even as mild as Ireland need some form of heating – even if it is a tiny fraction compared to a conventional building. As a example, my demonstration home, ‘Out of the Blue’, in Wicklow, uses just 10% of the heating energy compared to a conventional house, but it does need that 10%. So a passive house is not a zero-heating house, but a building that needs a very small back-up heating system and without the need for radiators or underfloor heating.

At a more technical level, there are three criteria that must be achieved in order to reach the passive house standard, as follows:
- Maximum annual space heating demand per square metre of 15 kWh
- Minimum airtightness of 0.6 air changes per hour measured at a pressure of 50 Pascal
- Maximum annual primary energy demand per square metre (for all electrical use, even white goods) of 120 kWh

So I would conclude that the passive house standard is a method of design and construction that delivers a building with a very low heating energy demand. Nothing more, nothing less. I will be giving a step by step guide on the main elements of the passive house over the next few weeks, so stand by.

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