What is a passive house?

A passive house is a home built to exacting design and construction standards which ensure minimum energy is used to heat it.

There have been more than 65,000 buildings designed, built and tested to this standard worldwide with over 1,000 in the UK (1), including the ground-breaking Goldsmith Street social housing development in Norwich, which won the prestigious Stirling Prize awarded by the Royal Institute of British Architects.

For some, passive house standard is seen as the only realistic way currently to achieve the goal of zero carbon housing in the UK as a central element in the drive to Net Zero by 2050. For others, it would be a key part of the overall zero carbon strategy in the coming decades.

Goldsmith Street

As an example of what can be achieved with intelligent, environmentally focused design, the Passive House development in Goldsmith Street, Norwich is extraordinary. It’s a superb model for energy-efficient social housing that could be readily copied throughout the UK. The terraced homes were built directly by the council and rented with secure tenancies at fixed social rents.

The RIBA Stirling Prize judges described it as “a modest masterpiece, representing high-quality architecture in its purest, most environmentally and socially conscious form”. Designed by London firm Mikhail Riches with Cathy Hawley, the 105 cream-brick homes have energy costs that are around 70% cheaper than average. Heating bills could be as little as £150 a year. (2)

The walls are fully insulated and the roofs are angled at 15 degrees so that each terrace does not block sunlight from the homes behind. Other elements include letterboxes built into external porches, rather than front doors to avoid heat loss through draughts.

Fossil-fuel free heat

The Passive House concept first took form in discussions between Swedish and German academics, developing into the Passivhaus movement, informed at first around North American house building experiments of the 1970s in response to the oil embargo and rocketing fuel costs. These homes attempted to use little or no carbon fuels, relying instead on solar and other energy forms.

The first Passivhaus homes were built in Darmstadt, Germany in 1990 and the Passivhaus-Institut was founded there six years later to promote and control the standard. And there is a consortium supported by the EU that is actively promoting the standard.

Passive House buildings must achieve a 75% reduction in space heating requirements, compared to standard practice for UK new build. In designing and constructing a Passive House, the aim is to reduce the heating requirement so that inefficient, large conventional heating systems are not needed. The building will maintain constant temperatures and avoid the need to burn fossil fuels for heating and cooling.

In this passive mode, the heat generated from “free” sources like the sun, human occupants, household appliances, lights and the heat from the extract air cover a large part of the heating demand. This is sustained through the excellent insulation and airtightness of the structure.

Heat recovery

The passive house uses a mechanical ventilation system, with an air-to-air heat recovery component, delivering fresh air and removing stale air. Air being expelled goes through the heat recovery ventilator, which transfers the heat to the incoming fresh air.

The Passive House standard has three requirements for certification:

Space heating demand cannot exceed 1.4 kWh / sq. ft. / year
Air-tightness pressurization (blower door test) cannot exceed 0.6 air changes per hour at 50 pascal pressure
Total source energy including domestic electricity cannot exceed 11 kW / sq. ft. / year.

Applying the exacting standard to retrofits is complex but has been achieved through detailed planning and design that avoids issues with thermal bridges, along with selection of quality building components, superior insulation, ventilation with heat recovery and airtight construction.

Relaxed retrofit

EnerPHit is a more relaxed retrofit standard for buildings where architecture and conservation requirements rule out full Passive House standard application, allowing thermal bridging, with lower airtightness and heating demand criteria.

For those of us who can only dream of having the resources for painstaking retrofits, there are still many ways to reduce energy demands, including a focus on the highest levels of insulation and choosing high-performance windows and doors with insulated frames, along with solar panels for water heating and electricity.

We can also consider a boiler upgrade if it is getting old and can fit smart controls on radiators, which are an effective way of managing heat more efficiently. If you use oil heaters, then a more effective form of heating is a far infrared panel, which heats objects rather than the air.

And to ensure we have the most energy-efficient home, we can fit LED lights that consumer 80% less electricity than standard bulbs, as well as fitting eco taps and shower heads that reduce water-heating needs by 60%.

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