How PU can be used in Passive House projects

Passive House principles have been adopted and proven across Europe and are increasingly being employed in the UK to deliver buildings that are energy efficient, comfortable and affordable at the same time.



hat was once a niche approach to building, but now proven on a whole raft of building types from houses to schools, offices to apartment buildings, a key feature of this tried and true construction concept is that it incorporates very high standards of insulation. But then does an energy-efficient building with a very well insulated building fabric provide its occupants with a comfortable and healthy indoor air environment throughout the year?

Polyurethane insulation materials are often used by architects and designers to create a highly-insulated building fabric and are compatible with maximum levels of energy efficiency required for Passive House certification. For an ongoing project launched in Belgium in 2011, the potential of using polyurethane materials has shown the environmental and economic benefits of this method.

Developed by ISOPA, the European trade body for diisocyanate and polyol producers, the end-of-terrace four-storey family house was completed in Evere near Brussels in 2013. It is now occupied and working as a low-energy test bed; its running costs and energy use closely measured to show the savings possible for homeowners.

One of over 12,000 new build Passive House certified buildings across Europe, the ISOPA house is unusual in using a high proportion of PU to achieve its highly insulating fabric first design which reduces the need for heating and saves around 80% of the energy used by a normal house. PU insulation has been used wherever possible, including in the cavity between the brick and block wall at a depth of 18cm achieving a 0.124 W/m²K U-value. A similar depth has also been applied in two PIR board layers at a depth of 25cm between the concrete ground floor and the screed, which has underfloor heating embedded in it. Windows are highly-insulated PVC frames with a PU core and the roof is also insulated using PIR board. Furthermore, all concrete slabs on the first and second floor are insulated using PUR spray foam as they also have radiant heating.

The house has been designed so that all of the construction elements work together in an integrated way, from the solar panels on the roof to the geothermal heat pump and the MVHR system which ensures that warm fresh air circulates internally despite the high air tightness levels. The University of Leuven has been evaluating the house’s overall performance, energy use and indoor comfort levels, which would verify whether the PU products as installed were really achieving the calculated performance levels.

Leuven University performed a co-heating test on the empty building, which measured the heat input necessary to keep the house at a constantly elevated set temperature. By plotting the energy use against indoor-outdoor temperature differences, an estimate of the heat losses through the building fabric was made. The analysis of the data yielded an estimated heat loss coefficient of 60.0 W/K, with a standard deviation of 3.0 W/K. This indicates that the thermal performance of the building fabric meets the very high standards expected, which was instrumental to the project reaching the performance levels required for Passive House certification.

Polyurethanes are ideal for Passive House construction because they provide very high levels of insulation thanks to low thermal conductivity, meaning they provide reduced thickness, increasing their affordability and reducing the impact on building footprints. As well as requiring fewer adjustments to be made to the design of buildings and less aesthetic compromises, such as with deep window reveals, further cost savings on depth of eaves, joists, rafters or studs, lengths of fixings can be achieved. In short, the extremely low U-values required for Passive House projects can be much more easily achieved with PU than with other materials as far fewer changes to design detailing are required.

Rigid PIR insulation boards are also light but strong, moisture-resistant and easy to install, and they, as well as spray foam PUR insulation, retain their insulating properties for the life of the building. Last but not least, PU materials contribute to preservation of natural resources by reducing the need for energy, which assists their sustainability credentials in Passive House projects.

Creating practical ‘near zero energy’ houses are essential if we are to meet the Climate Change Act and reduce our carbon emissions 80% by 2050. With houses accounting for 40% of energy consumed across Europe, achieving the means of constructing new Passive Houses affordably using PU, which can deliver the results while saving homeowners money, is the realistic way forward, as demonstrated at the Polyurethanes Passive House.

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