The Passivhaus approach

Over 30,000 buildings worldwide are accredited to the Passivhaus standard, with that figure continuing to rise as the global pressure to create energy-efficient buildings increases. Here Nicolas Tye, Director at Nicolas Tye Architects, shares his insight into the approach architects can take when designing and building Passivhaus-accredited buildings for both the residential and commercial sectors, particularly with regard to the importance of rooflights.

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ounded in the early 1990s in Germany by the Passive House Institute (PHI), the Passivhaus standard is a construction concept that aims to significantly reduce a building’s ecological footprint, whilst also ensuring the property is comfortable and affordable.

Initially considered a ‘trend’, the Passivhaus standard has evolved into an industry-leading standard, with my architectural practice, along with many others across Europe, seeing an increase in interest for both private and public buildings where the primary design influence is for the construction to be as environmentally-friendly as possible.

Whilst we originally received requests for one-off private dwellings looking to achieve the Passivhaus standard to primarily cut heating bills, there has been a significant influx in recent years for projects within the local authority environment, such as schools and other commercial buildings, to be built to the Passivhaus standard. Of the residential projects, there’s an interesting divide between those who are striving to officially achieve the Passivhaus standard and those who are simply influenced by the practice and are wanting to create a thermally-efficient home without having to go through the procedure of an official accreditation.

This is indicative of the positive impact the Passivhaus standard is having on both Europe and specifically the UK, as homeowners and local authorities are increasingly looking to construct buildings led by ecological designs to provide cleaner air inside. As the Passivhaus standard supports the construction of entirely energy-efficient buildings that minimise ‘heating demand’ by using energy sources from inside the property, such as the body heat from residents or solar heat that enters through windows, it eliminates the traditional requirement for heating and manual ventilation systems. This dramatically reduces energy use and carbon emissions, which subsequently decreases energy costs, whilst also supporting the building’s ongoing health and overall indoor air quality.

To achieve a Passivhaus-accredited build, an alternative approach must be taken with regard to the building’s overall design, reconsidering the quality and performance of the building components specified. There are five main areas that architects should consider when undertaking a Passivhaus build: airtightness, thermal bridge-free design, thermal insulation, Passivhaus windows and adequate ventilation with heat recovery.

In response to the building’s envelope, focusing on the Passivhaus windows section, in particular, the PHI outlines that the recommended maximum U-values for walls, floors and roofs is 0.15W/m²K. With regard to roofs, all building materials must offer maximum energy efficiency, whilst also diminishing the loss of heat. As the roof is one of the main areas where heat is lost due to radiation, the addition of rooflights can play an important part in maximising energy efficiency.

The PHI states that the highest U-value for complete window installations remains at 0.85W/m²K, requiring the specification of rooflights that do not exceed this maximum U-value. To achieve this, we work with manufacturers such as Roof Maker, who offer a Passivhaus-accredited fixed flat rooflight with a U-value of 0.2W/m²K. Specifying products such as the above ensures we can be confident we are well within the PHI’s requirements to achieve complete energy and solar gain efficiencies, without compromising on the aesthetics and overall design of the space.

However, the installation of windows, doors and rooflights can often be where the greatest level of energy is expected to be lost, due to the glazing present, along with the breaks between the frame and the glass where there is the opportunity for heat to escape. Therefore, the frames must be well-insulated and fitted with low-E glazing filled with argon or krypton to prevent heat transfer. For most cool-temperate climates, this requires a U-value of 0.80W/m²K or less, with G-values around 50%.

The inclusion of rooflights within the ceiling and roof design of a Passivhaus building can not only support and increase the thermal performance of the property but also ensure natural light is maximised for additional interior comfort, both physical and thermal.

For architects, it’s important to find that balance between establishing an ecological design that doesn’t impede on personality or creativity, whilst also specifying the highest standard but most affordable products. Following the five design principles offers a strong blueprint with which to begin, to ensure all key elements are not only adhered to but seamlessly integrated into the build itself.

As the PHI states, Passivhaus is a “building standard that is truly energy-efficient, comfortable, affordable and ecological at the same time”, architects can revolutionise the expectations and realisations of both residential and commercial constructions to pave the way for a more energy-efficient future.

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