Passive House – Optimise, Not Maximise

Why Passive House?  In 2015, the Paris Climate Conference (COP21) produced a global consensus agreement addressing climate change.  This agreement represented the widely, though unfortunately, not universal (ahem, Mr Trump) understanding that the need to cut greenhouse gas emissions is an urgent issue facing us all.

To emphasise the issue, greenhouse gas emissions (GHG) from the building sector alone have more than doubled since 1970, to reach 19% of global GHG emissions in 2010 (see the chart below).  According to Environment and Climate Change Canada, the building sector was the third largest contributor to emissions in Canada in 2015.  Reducing these values is crucial.

In a local effort to address this issue, the City of Vancouver has recently passed a mandate to become the greenest city in the world by 2020.  The measurement metric they have chosen to achieve this title is demonstrable reductions in carbon emissions.  The first step is a reduction in energy use – improving efficiency and reducing demand are widely considered as the most promising, fastest, cheapest, and safest means to limit emissions and mitigate climate change.

This may be achieved through a variety of means, however the Passive House standard represents a proven, quality assured methodology.  As such, design and construction to the Passive House standard is now one of two low energy compliance paths compulsory in Vancouver for any publicly funded projects, or in any project requiring rezoning – zoning by law reclassifications, required to build alternate building types or to place additional density on a previously low density site.

Passive House (or Passivhaus if you prefer) is not a brand name – it is not really about passive design, nor is it about simply houses.  It is not a point or credit system, but rather is a methodology for the design and construction of buildings that use very little energy to heat and cool a building.  It is a quality assured building energy performance standard, plain and simple, with real, measurable reductions in energy use, and hence, reductions in emissions.

It’s a standard that can work equally well in cold climates as it can in hot climates – but it isn’t a one size fits all solution.  Passive House is really about creating the optimal design response specific to the site, location, and typology.  In simplistic terms, Passive House is a balancing act between how much heat is being gained and lost in a building.  Passive House is really about optimisation.

From a design perspective, before putting pen to paper, it is important to first understand the basic concepts and methodologies of Passive House.  Design of a Passive House is essentially about understanding the implications of each design move made.  Succinctly summarized by Elrond Burrell, Passivhaus in Plain English and More (www.elrondburrell.com) an experienced architect and Passive House writer, there are five principles about Passive House that you need to get right, before you delve into the technical.  These principles are methodology, location, orientation, form, and construction.  The design process is much simpler the more you understand and adapt to these basic principles.

The design brief in a Passive House project is very similar to any other project, however with the added nuance of having strict energy use limitations.  Like designing to a cost budget, designing to the Passive House standard essentially means you are also designing to a strict energy budget.  Avoiding expensive and impractical design decisions from the outset and designing with thoughtfulness, practicality and rigour are keys to success.

Targeting an energy efficient design suggests a design that is efficient in its form.  If the form is more expansive and sprawling, or with extraneous jigs and jogs, the problem gets that much more difficult.  Passive House may still be achievable, but generally with more and more insulation, and thus, greater cost.  Optimised design is key.  In general terms, a simple form creates a simpler and more cost effective path to Passive House performance.  Basically, when looking at design options, if the exterior wall area of one highly articulated option is double that of another, the insulation and performance values will be double as well.  Surface area matters.

It is also important to note that a Passive House is fundamentally different from a passive solar house.  Solar gain is important in a Passive House, however the impacts must be understood to be managed.  The key is to keep the heat where you want it… either in or out, optimised to suit, and balanced with all other energy sources.  In a Passive House, the shell or envelope enclosure is nearly the same – airtight, well insulated, with high performance glazing.  As everyone knows, the basic difference is that in cold climates, the building is oriented to open to the sun, and in hot climates, you protect the building from the sun.  As best stated by Aeschylus (524 – 456 BC), “Only primitives and barbarians lack knowledge of houses turned to face the winter sun.”

Not to be confused with the five design principles, a Passive House building will feature five basic technical aspects.  These are – a high performance and well insulated building envelope, airtight construction (pressure tested and verified), thermal bridge free construction, high performance glazing and high efficiency heat / humidity recovery ventilation.  These are integral to achieving the promised energy performance.

Fundamentally, Passive House is an envelope first approach to sustainable design that is entirely performance based.  It is fundamentally about design, best approached as part of an integrated, iterative design process, with ongoing modelling of the design to a level of detail appropriate to the design stage.  There are no materials or methods prescribed as to how to build the standard, but rather only the required performance metrics.