The Passivhaus method
The Passivhaus method Developed in 1996, five years after the first experimental PassivHaus project in Germany, the PassivHaus standard relies upon a very simple set of criteria; i.e. very high levels of insulation, the elimination of cold bridges, thermally broken triple glazed windows orientated to the south to maximise passive solar gain, and an incredibly well sealed building fabric. It is estimated that using the PassivHaus method to construct a typical house results in a 90% reduction of carbon emissions compared to that of an average home.
Concrete brings major benefits to the passive eco design, in the exploitation of its thermal mass. All components of the exterior shell of a Passivhaus are insulated to achieve a U-Value that does not exceed 0.15 W/m2/K – typical house is around 0.25 to 0.35. The thermal mass of concrete helps store large amounts of heat and then release this heat back into the building footprint which in turn helps to maintain and control the internal temperature of the building without the use of traditional central heating, hence the term, ‘Passiv’.
England's first Passivhaus
Aggregate Industries are proud to have been involved in the first certified Passivhaus in England which was featured in an episode of the Grand Designs programme in 2010.
The Underhill Passivhaus is located just outside the market town of Moreton-In-Marsh in Gloucestershire. The house built into a hillside and has been constructed underneath a 300 year old listed stone barn. The house is hidden from the surrounding countryside by having the excavated hillside built back on top of the precast concrete framed house.
The offsite precast concrete panels used on the project demonstrate sustainability and innovation and forms a monolithic structure which is naturally airtight and minimises air leakage through the joints by using insitu grouting. Air leakage through the fabric must be less than 0.6 times the volume of the house per hour (this is the equivalent of an air permeability value of less than 1m3/hr/m2 @ 50 Pa). This equates to approximately a factor 10x better than a typical new-built.
The precast solid walls were then externally insulated using EPS insulation sheets to achieve a U value of 0.15 W/m2degk and exposed external walls received a thin coat render system to finish.
The use of a precast concrete panelised system also gave all of the benefits of off-site construction, with reduced wastage and a fast-track programme, but also of course provided a superior interior finish, important because much of it is actually exposed internally.