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What is Passivhaus and why does it matter?

What is Passivhaus

The energy consumption timebomb

In September 2017, the world took a battering. Tropical Storm Harvey wrought devastation on Houston, Texas. Hurricane Irma flattened Barbuda in the Caribbean. In India, Mumbai ground to a halt under waist-high flooding, and monsoons killed more than 1,200 people in north India, Bangladesh and Nepal.

For decades, scientists have been warning about climate change. One of the long-predicted outcomes is that we’re going to see more of these extreme weather events, and the destruction that goes with them.

We’ve lived through a period when fossil fuels were cheap and seemingly endless. And for decades, we designed buildings where reducing power consumption fell way down the priority list. But the world is changing. Rampant energy consumption is becoming a serious issue as we look for ways to reduce our dependence on fossil fuels.

Architecture’s dirty secret

In the UK (in 2010), 40% of the country’s total energy usage was taken up by buildings, and 60% of that was for heating and cooling. The built environment produces nearly half of our carbon dioxide emissions.

When it comes to thermal insulation, our homes, offices and factories are woefully inefficient. To address this issue with existing buildings, the government introduced schemes to improve insulation and, therefore, lower energy consumption. Recent programmes included offering free cavity wall and loft insulation to homeowners.

One of the ways architectural designers and scientists have come together to reduce energy usage in new buildings is by developing a standard called Passivhaus.

What is Passivhaus?

Established in Germany in the early 1990s, the Passivhaus Institute developed a standard for the design and construction of homes and offices that consume a fraction of the energy used by traditional structures. A Passivhaus-rated building aims to provide highly energy-efficient, comfortable and affordable spaces for living and working.

Take-up started slowly slow but is growing. Since the millennium over 30,000 Passivhaus-rated buildings have been constructed.

Passivhaus specifies building techniques and materials which significantly reduce the need for heating and cooling systems. Homes and offices are warmed by the sun’s heat through glazing and are cooled by shading during the summer months. Passivhaus buildings are extensively insulated, and draughts are eliminated, creating an airtight environment.

One of the main aims of the Passivhaus standard is to create a comfortable internal living temperature. This consistent atmosphere is achieved using a mechanical ventilator and heat exchanger which recirculates the air and recovers heat from it. In a conventional house, the biggest cause of heat loss is ventilation. A Passivhaus ventilation system decreases this heat loss by 80%, while at the same time eliminating the problems caused by damp and mould.

What are the benefits of living in a Passivhaus?

Dramatically lower energy bills. Passivhaus buildings do not use traditional heating systems or require fireplaces. To achieve Passivhaus certification, a building must consume less than 15kWh/m2 of electricity per year. A typical semi-detached house in the UK consumes 17 times this amount.

Improved indoor air quality. The highly efficient Passivhaus ventilation system manages humidity levels by balancing rooms with high air moisture content, such as kitchens and bathrooms, with other areas such as living rooms and bedrooms. The system also introduces fresh air from outside which is filtered, removing dust and allergens.

Comfort levels. The Passivhaus standard sets an explicit target for consistent living temperatures throughout the home. The ventilation system manages humidity and air quality, and the building’s construction eliminates draughts.

Peace. Due to the highly insulated nature of a Passivhaus home, and the use of high-performance windows and doors, exterior noise is reduced substantially. The standard also stipulates that the ventilation system operate quietly.

Long-term value. While the design and construction costs of a Passivhaus house will be 10-15% higher than for a conventional home, the standard can reduce your heating costs by up to 90% indefinitely. A recent British study concluded that taken over the 25-year life of a mortgage, a homeowner would be better off building a Passivhaus home than a comparable sized traditional house.

Is it possible to apply the Passivhaus standard to an existing building?

A small number of existing homes have been retrofitted to meet the Passivhaus standard. However, the requirements for energy efficiency and airtightness are tough to achieve.

In recognition of this, a new energy performance standard, known as EnerPHit, was launched in 2011. EnerPHit sets less stringent requirements to allow retrofit properties to become certified as Passivhaus.

Retrofitting is not for the faint-hearted. The process is very invasive, involving stripping back walls and removing ceilings to get to the bare internal structure of the house. The costs involved may make retrofitting prohibitive.

How do I build a Passivhaus property?

Building to Passivhaus standard is not without issues, especially in the UK. The key to delivering a successful Passivhaus building lies with assembling the right team at the start of the project. Because the design principles of a Passivhaus build are substantially different from those of a traditional house, you should select a designer with experience of working with Passivhaus standards.

The builders you choose will most likely be unfamiliar with the construction methods. You may need to import key components, such as the windows and the ventilation system, from abroad. Constructing an airtight building requires a systematic approach and close attention to detail – hence the 10-15% premium in project costs compared to building a standard home.

The cost of construction should become more competitive with the completion of greater numbers of Passivhaus projects. These costs should lessen still as our demands for low-carbon, energy-efficient products increases.

As we begin to reduce our dependence on fossil fuels, the Passivhaus standard points to a future for buildings that allow us to live in comfort, at a cost that is sustainable to ourselves and the environment.

For more information about Passivhaus, see this video interview with Wolfgang Feist from the Passivhaus Institute.

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Photo credits:

“Passivhaus in Holzriegelbauweise” by Pichler Haus (Own work) [CC BY-SA 3.0], via Wikimedia Commons

“Prescott Passive House” by Studio804 (Own work) [CC BY-SA 4.0], via Wikimedia Commons

“Original Passivhaus, Darmstadt, in winter” by Passivhaus Institut [CC-BY-SA-3.0], via Wikimedia Commons.


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