Passivhaus, or Passive House, was originally all about saving energy, and sets strict limits on heat loss and air infiltration. The very rich people in this world don’t worry much about energy costs, yet more and more of the nicest houses in the world are being built to Passivhaus standards. One incredible example is this Bloomsbury Town House in London, renovated by Prewett Bizley Architects.
Originally built in 1820 and previously used as office space, the architects, working with interior designer Emily Bizley, restored it to single family glory. It also had “the added ambitious target of pushing its energy efficiency towards Passivhaus Enerphit standard.”
Enerphit is a standard developed for renovations, and slightly relaxed from the Passivhaus standard. It’s still tough, and even though it appears that they missed the airtightness test by just a bit, the results are still spectacular.
Our work has transformed the energy efficiency of the house, reducing the overall space heating demand by 95% from 160kWhr/m2a to 20kWhr/m2a, and the air leakage from 8 to 1.0 ACH. The energy strategy relies on an intricately planned and installed insulation approach and an advanced secondary glazing system developed for this house with a leading supplier.
Sometimes the goals of those in the architectural preservation world clash with those in the energy conservation world, and in this case it appears to have been quite the battle; according to the Architects Journal:
Although the sash windows were not original, having been replaced in the Victorian era, they nevertheless proved a sticking point for the local authority conservation officer and had to be maintained. A triple-glazed Passivhaus certified sash system is available, but was deemed unsuitable because of its frame thickness. It took a year and a half of careful negotiation to allow the original window surrounds to be dismantled and reassembled with secondary glazing incorporated between the restored sash window and shutter, which helped partially conceal the new frame. Thermally insulating evacuated glass has been set into a slim timber frame for improved performance and narrow sightlines….‘It took three more applications until eventually permission was granted after we had been on site for eight months,’ recalls Prewett.
There is a lot to read between the lines in that paragraph; anyone who cares about architectural preservation (and I am past president of the Architectural Conservancy of Ontario, where I fought these battles many times) knows that windows are the eyes into the soul of buildings. Old windows are also capable of being pretty energy efficient if restored, but not if you are aiming for anything near Passivhaus standard. So a lot of choices had to be made about how far to go to meet these tough standards.
This is a lot of work. If you don’t have to worry about the price of a few watt/hours, why bother going for Passivhaus or Enerphit? What’s the benefit in spending that time and money? New York architect Mike Ingui, who does a lot of high end renovations, explains that his clients love the quiet and the air quality, but also, since they are sharing walls with neighbours, the lack of dust and bugs coming through the party walls. Once you are building at this stratospheric level, the cost premium for going Enerphit or Passivhaus is pretty minimal. Sometimes Mike doesn’t even tell his clients he is doing Passivhaus; it is just his standard.
Robert Prewett tells the Architects Journal:
On the one hand there was a very technical side to do with energy efficiency and building physics. On the other there was the opportunity explore how historic and contemporary spaces could be woven together along with the technical issues.
It is a challenge. Passivhaus and Enerphit set difficult goals; Heritage preservationists are attacked all the time for letting silly things like windows stand in the way of energy conservation. Prewett Bizley have shown that one can achieve both. They also help make the point that Passivhaus isn’t just the best standard of efficiency; it is also the new standard for luxury.
More at Prewett Bizley.