A PassivHaus Renovation: Heritage Meets Energy Efficiency
In the UK and North America, heritage buildings are under serious threat; our history is being bulldozed under the false mantra of energy efficiency when in fact, most buildings can be insulated, sealed and brought up to a much higher standard without throwing away the embodied energy stored in those bricks.
That is why this Victorian terrace house in West London is so interesting; the builders are not just doing a renovation, but are going for the PassivHaus standard, tough to do in new construction and perhaps impossible in a heritage structure like this.
The PassivHaus standard is tough to meet; it requires a lot of insulation, really low air infiltration and a compact form. Old houses often meet the latter requirement but leak air like sieves.
Tom Pakenham (and Sophie, Baby Luke and the Green Tomato Team) are "charting the epic conversion of a draughty, freezing, solid brick walled Victorian house into a cosy, efficient and beautiful home for the 21st century." They hope to prove that "low-energy houses are not only much more comfortable living spaces than the old clunkers we live in now, but also don't have to look like a nuclear bunker."
There is a lot more than a lot of insulation going into this house; it has solar thermal, solar photovoltaics, (all carefully integrated into the slate roof) a green roof, ground tubes for preheating and precooling fresh makeup air; a green roof and rainwater harvesting.
Along the way, they have to fight with those nasty heritage officials who like chimneys and slate roofs and brick exteriors. Maintaining the historic character means that they have to insulate the front facade inside, with 130 mm of high efficiency rigid insulation. This eats up a lot of space, and these houses are not very big to start with. That is one reason so many older houses get wrapped in that horrible exterior styrofoam and stucco.
But there is another problem with interior insulation of this magnitude: heat loss through the exterior walls will be virtually eliminated. A little bit of heat loss through old brick walls drives out moisture; if you get rid of it completely, there is the possibility of freeze-thaw cycles causing the brick to deteriorate. Fortunately London doesn't get too many of these.
The new roof.
The real challenge with Passivhaus design is controlling air infiltration; the detailing around those bay windows will be interesting. Tom notes:
Because we are renovating and have to fill lots and lots of gaps and cracks, this component is likely to prove the biggest challenge. About halfway through the build, we will bring in a special door called a blower door and test the whole house for air leakage. We hope to fill or tape up any leaks that we find.
Good luck; it is almost like building a house within a house.
The PassivHaus standard is difficult to achieve, but is an important goal, using less than a tenth the energy of a typical home. To do it in a retrofit of a protected heritage building is a real accomplishment; I am not sure that it can be done, and I don't think Tom is either. But even if they get close, it is still a spectacular achievement. We will be watching closely.
More at the Ecohome by Green Tomato