Passivhaus at a crossroads?
The Passivhaus standard has been gaining serious traction; in the UK and elsewhere in northern Europe it is now the in ‘vogue’ standard for low energy/environmentally friendly construction.
The principles of the passivhaus or passive house concept are based on a simple postulation. That conserving heat energy, through insulation and reducing air permeability, is a more resource efficient means of maintaining a comfortable internal temperature, than converting higher forms of energy into heat. This has some strong grounding in basic physical principles, although achieving this requires our buildings to halt the essential entropic tendency, for heat energy to seek a state of equilibrium.
Great innovation in the levels of building fabric performance alongside a greater understanding of building physics, and mechanical ventilation technology, now means we are now able to maintain passivhaus homes without formal heating systems, even at high latitudes.
Crossway passivhaus, an architectural gem, but unlikley to be replicable for mass housing
A central tenet of the passivhaus approach is that it is also almost always cheaper to conserve heat, rather than create it, using other low carbon forms of energy. Thus this leads us to consider the two key goals of such an approach from an energy use perspective:
Conserve heat, reducing the cost of heating buildings, in an era of rising fuel prices and fuel poverty
Thus reduce combustion of greenhouse gases that are the major contributor to global climate change
This logic has informed the ‘energy hierarchy’, that now governs the approach to residential and commercial energy strategies in UK construction. However we must consider that this truism, does not always hold. I’m sure the reader can think of many examples where insulation methods such as bespoke high performance passivhaus windows, or tricky external insulation detailing, is far more expensive than installing solar PV panels for the same CO2 savings.
Indeed with PV panels continuing to fall in cost past £1k/kW, and the majority of passivhaus projects in the UK remaining for private self build enthusiasts, we have to ask ourselves what is passivhaus for and where is it going?
Almost uniquely in environmental problems, climate change and the impact of CO2 emissions are global in nature. Therefore unlike other environmental pollution problems, small localised reductions in emissions will have no impact, without the bigger picture changing.
Therefore we must consider that if the passivhaus standard is to deliver on the 2 key goals identified, it must achieve the following:
Be able to demonstrate the approach presents the most cost effective means of reducing domestic energy consumption and CO2 emissions
Be delivered at a scale that will make a significant impact to the climate change issue
Wimbish, Passivhaus social housing scheme, Essex
There are some encouraging signs as the passivhaus standard is being adopted in a number of social housing schemes of increasing scale across the UK and elsewhere. Many in the mainstream industry see passivhaus as a method that will never go mainstream, instead it will continue to inform conventional building standards by demonstrating best practice. However the key problem with this argument are that to see the cost benefits of adopting passivhaus principles, you really have to take thermal performance to a level where a wet central heating system is no longer needed. This allows for the estimated 15% increase in build cost from a passivhaus to be offset by saving £10k+ on a central heating system. So unless we can get a building down to around 10W/m2 peak heating load, we are stranded in an expensive place from a specification point of view.
The more schemes that demonstrate the standard can be achieved at a parity with a Part L compliant specification, the stronger this argument will become. Perhaps a key driver of this scenario is for local authorities to begin to specify the PH standard, vis a vis the code for sustainable homes, pre-housing standards review. However in an era of deregulation this seems increasingly unlikely.
Without a deployment for the masses passivhaus could remain a niche standard for enthusiast and dare I say it the borgousie, with the time and money to undertake their own ‘grand design’. The standard has great potential and elements that could enable deployment at mass scale, however we need to begin thinking in a more strategic way if this potential is to be realised. Everyone deserves a healthy and comfortable place to live, therefore policy-makers should aim high, and consider how Passivhaus might make a contribution a few orders of magnitude more than it has currently.
Quo Vardis Passivhaus?
Sustaianbilty Director SDC Ltd