A proactive approach to a Passive House
‘Passive House’ is a standard for a cost-effective, low-energy construction concept that produces buildings with remarkable energy efficiency qualities without compromising on comfort.
With all of the necessary information published freely on-line, it is claimed that any competent architect can design a Passive House. The standard is also relevant to non-residential buildings such as schools and offices. While it is most simply achieved with a new-build, it can also be successfully applied during a major building renovation.
Passive House buildings combine the use of energy efficient materials, a very high level of floor, window, roof and wall insulation and an airtight design. They are designed to be ‘thermal bridge free’, meaning the insulation has no cold corners or weak spots, reducing any problems with condensation. Ventilation is nevertheless essential, and an unobtrusive system supplies constant fresh air to maintain high levels of internal air quality without creating draughts. It incorporates a highly efficient heat recovery unit that captures heat for re-use in the building.
The designers ensure that the building makes such efficient use of the sun, internal heat sources such as domestic appliances and heat recovery that a conventional heating system is unnecessary, even on the coldest days of winter. This is what defines a Passive House. During the summer, passive techniques such as strategic shading help to keep the building comfortably cool.
Tests and calculations on existing Passive House dwellings are producing some impressive data. Measurements carried out on more than a hundred Passive House properties in central Europe as part of the European Union’s CEPHEUS project showed average energy savings of approximately 90% by comparison with traditional building stock, and 75% savings against new-build equivalents.
As a result, Passive Houses are environmentally friendly by definition. While some additional energy may be required initially for their materials and construction, this is insignificant by comparison with the energy savings they enable throughout the life of the building.
Similarly, the necessary financial investment in high quality materials and design required by the Passive House standard will be offset by the greatly reduced cost of installing and running heating and cooling systems. Calculations for German Passive Houses suggest that initial construction costs are now only approximately 5% higher than those of a comparable traditionally built house. Payback periods of course depend on the size and construction cost of the building, but under most circumstances the reduced running costs are likely to offset the construction costs in two to three decades, even allowing for loan repayments.
The Building Research Establishment (BRE) is one of the certifying bodies for Passive Houses, and there are fewer than a hundred of its Passivhaus buildings in the UK. The ‘Sleepy Dorset’ blog (here) tells the story of one family’s self-build Passive House since 2016 and its successful achievement of Passivhaus status. It relates how the house performed in Dorset’s coldest winter weather for many years in March 2018, and how the family awoke each morning to a comfortable 18ºC without any heating, despite outside temperatures of -6ºC and thick snow.