An introduction to Passivhaus
If you’ve taken an interest in modern building construction or watched ‘Grand Designs’ (Channel 4) in the past couple of years, you’ll have been hard-pressed to have missed the term Passivhaus being flung around, but what does it mean?
Regarded as the gold standard of energy efficiency, Passivhaus is a voluntary standard for a house’s energy efficiency rating.
Developed in Germany in the 1990’s, it translates to ‘passive house’ in English, and its purpose is to construct houses in a way that meets rigorous energy efficient design standards. This enables a building to maintain a constant temperature with minimal involvement of heating or cooling systems, thereby reducing the energy consumption and environmental impact.
Principles of Passivhaus design criteria aim to ensure the most cost-effective and robust methods of achieving low-carbon buildings through a combination of maximising insulation, strengthening airtightness, thermal bridging, and passive solar gain to reduce heating loss and minimise the need for heating input.
What are the key criteria for Passivhaus certification?
In order to qualify for Passivhaus certification, builders need to meet the following criteria:
- The exterior insulation must achieve a U value of less than 0.15 W/m2K
- Windows must have energy efficient glazing and frames should have U-values no greater than 0.80 W/m2K
- To achieve air tightness, the air leakage created through unsealed joints must not exceed 0.6 times a room’s volume per hour and a pressure differential of air changes 50 Pa (equivalent of an air permeability of less than 1m3/m2/h @50 Pa)
- Passivhaus ventilation must have over 80% of heat recovery from ventilation exhaust air, using an air-to-air heat exchanger
- A Passivhaus building should have a simple compact shape to minimise the external surface of the building in comparison to the internal floor area.
- The total energy demand for any space heating or cooling should be less than 15 kWh/m2/yr for the treated floor area
- The primary energy use for all appliances, domestic hot water, and space heating and cooling should equal less than 120 kWh/m2/year
For more information on Passivhaus criteria visit: www.passivhaustrust.org.uk
What are the benefits of Passivhaus?
Passivhaus designs have multifaceted benefits which appeal to different stakeholders. At a macro level the Passivhaus build criteria has the potential to improve building performance by lowering energy demand while retaining comfort levels for the occupant. With the use of renewable energy installations such as solar power, many passive house builds have the potential to generate more energy than they consume, achieving net zero status and aligning with the UK’s target of reaching net zero by 2050.
While the initial construction cost may be higher than conventional methods, the long-term drop in energy consumption and reduced energy costs associated with Passivhaus outweigh the initial building costs. Additionally, Passivhaus design principles pose a promising solution to the social housing sector amidst the UK’s ongoing struggle with fuel poverty.
The reduced utility bill costs could conceivably alleviate the burden of overwhelming fuel costs for lower income households and could eliminate the challenge of heating homes, while still trying to make ends meet.
However, with the majority of the UK housing being of older stock, consideration needs to be taken on whether buildings can be retrofitted to incorporate these energy saving methods and meet Passivhaus standards.
Can you retrofit a building to Passivhaus standards?
There are numerous Passivhaus developments already erected and in the works across the UK, however the task of introducing Passivhaus techniques into pre-existing building presents its own challenge.
Retrofitting requires making alterations to an existing building to improve its energy efficiency. However, each home is different, with the UK’s housing ranging from various periods in time and incorporating different building materials and techniques, it’s not a one-size-fits-all solution. What energy efficiency measures may work for one project may not be appropriate for another, and before any retrofit work is carried out, a ‘whole house’ retrofit assessment should be done to ensure that the retrofit does not result in damaging the building fabric.
While the principles of Passivhaus design can be applied to any building, it is unlikely you will be able to get the same results from older buildings than newer builds as considerations such as the building’s orientation and shape cannot be applied to existing structures. However, to accommodate for these limitations in older structures the passive house standard includes a retrofit standard called EnerPHit which provides revised criteria for retrofit work.
If you would like to enquire about SDL Surveying’s retrofit services, visit: https://sdlsurveying.co.uk/home-energy/retrofit-services/
For more information on EnerPhit see: https://www.passivhaustrust.org.uk/