What is Passive House?

Traditional homes (especially in the UK!) are poorly insulated, draughty, prone to condensation, costly to heat and – as a result - uncomfortable to live in.  The Passive House approach changes all of that. These are the key principles:

 

Insulation: The starting point for creating a Passive House is high standards of insulation to reduce heat loss. As a result very little energy is needed to heat the home. This isn’t just about insulating the attic and the walls – it’s about insulating the WHOLE building envelope, including the floor.  For new buildings it’s reasonably easy to do this without ‘thermal bridges’ (where the outside is connected directly to the inside of the building, allowing heat to escape and cold to penetrate).  For retrofits like my EcoBungalow, achieving continuous insulation is a lot harder – so there will be compromises and some thermal bridging.

 

Air Tightness: To work properly, a well-insulated home needs to avoid accidental air leakage.  Think of all the holes in the external walls in a traditional house – where pipes to the kitchen sink connect, where the toilet drains, even the letterbox.  All of these result in warm air escaping the building and cold air entering.  Not very efficient! So a Passive House is not only well insulated, it’s also as air tight as possible.  If you’re a hill walker like me, you’ll know that putting on a fluffy fleece will help you keep warm but – if it’s windy – the cold air whistles straight through the insulating fleece and you lose all the benefits.  So you put a windproof jacket on top and – hey presto – the fleece can do its job of keeping you warm. It’s the same principle for Passive House air tightness.

 

Ventilation: ‘But if your house is airtight, won’t you get condensation?’ is a question I’m often asked. Airtight doesn’t mean that there’s no ventilation.  It means that the ventilation is carefully controlled, and not haphazard. This is achieved through Mechanical Ventilation with Heat Recovery (MVHR), a system that supplies fresh air from outside, warming it with the heat of outgoing stale air. People tend to recoil at the term ‘mechanical’ – in reality, MVHR is whisper quiet and provides the home with filtered air, resulting in much better internal air quality than a standard home.

 

Energy sources: The key principles of Passive House is to REDUCE the need for energy through insulation, air tightness and controlled ventilation. So there isn’t a single prescribed approach to energy generation.  Like many retrofit projects, the EcoBungalow will have an air source heat pump to provide space heating and hot water.  If the budget can stretch to it, there may be some Photovoltaics to generate electricity.