Does Passive House Require a New Design Language?

 Architect Paul McAlister

Architect Paul McAlister

The movement of building standards towards passive house and rising fuel prices are the main initiatives driving the construction industry in the direction of certified passive house standard within Northern Ireland. It is an attractive aspiration for us within the construction and design industry to be at the forefront of low carbon design and passive house design in Northern Ireland, whilst making positive contributions to C02 emissions. Fully pursuing this standard within this industry would also open up export markets for our knowledge, skills and products, however in any potential advance towards an implementation of passive house there are many issues to be considered. The first issue is the capital cost of a passive house build. It is not possible to put a figure on the extra cost for a passive house building over a conventional building which barely complies with the 2008 Building Regulations. This would be far too simplistic. Cost depends on a whole host of variables, which includes the private residential sector, passive house clients generally insist on high quality fixtures and fittings. For example, the extra cost for passive house standard windows over standard triple glazed windows, may be due to improved functionality alongside achieving the energy standard and the criteria of passive house certification.

Those taking up the challenge and aspiring to build to passive house standard should have a clear idea of the budget limitations surrounding their project and the space requirements that budget will deliver. However, many designs, despite the best efforts to optimise design and energy modelling, will always fall short of certification. Often additional improvements which move the design towards certification don’t quite make the passive house threshold for space heating demand of 15kWh/m2/yr. Having a heat demand slightly higher than the threshold, at say 18kWh/m2/yr may have slightly higher running costs, but they are minimal when compared with capital costs of finding the final 3-5kWh in some cases. Each individual project must weigh up their capital expenditure versus running costs to decide what is best for them. When the site condi­tions and design strategy produce a performance for heat demand that falls inside the passive house criteria then certification becomes a simpler process. However if the threshold is missed by a few kilowatt hours, resulting in the design being un­able to deliver the space heating solely through the ventilation system, it may be better suited to add a secondary heat source whilst still achieving a high performance building. With unusually cooler winters predicted for the coming decade, having some extra, user-controlled, heat contributors such as the addition of a couple of radiators may be beneficial.

Another issue of the application of passive house is design, which by its nature is subjective to the client and architect. A number of bespoke, architect-designed homes are being certified within Northern Ireland, which is a promising sight. However it is difficult to imagine standard ‘off the shelf’ designs being replaced with homes designed to optimise site and energy performance. Passive house can be adapted to every conceivable style of building with the emphasis placed by the passive house modelling tool on efficient building envelopes and internal layout and orientation. This could place added expense on those restricted to single storey buildings by planning. The proposition as to whether or not ultra-low energy buildings will require a new design language and how they will contribute to urban and rural landscapes is an unknown factor. It is important that planners are educated to recognise this new typology of building that may deviate in form from designs favoured today for example, by having a design that does not necessarily face the road.

The regulatory compliance, concerned with the recognition of passive house can be an issue. The two equivalent energy performance methodologies within building regulations have shared objectives to considerably reduce energy use, but actually have conflicting methods. Passive house comes with a difficult certification process, requiring air leakage testing after completion and evidence of installed insulation. It provides a model for inspection of low energy builds to ensure that adequate attention to detail is applied. Passive house prioritises minimisation of heat loss above all else, while the SAP methodology for Part F compli­ance is not as strict on fabric and ventilation heat loss but puts a high emphasis on the use of renewables. The English version of Part L 2011 came into effect in October 2010 with enhanced standards of performance required. A proposed solution to these conflicting methodologies is that the passive house standard could be recog­nised as an alternative method of compliance with the new Part L. This could provide a pos­sible strategic move by government to support the potential of the pas­sive house building sector by moving building regulation in line with the requirement of passive house certification.

The final issue concerns knowledge of pas­sive house building procedure. There is an education process needed to show how passive house standard buildings and its retrofit equivalent EnerPHit are achieved. The responsibility of propagating this information needs to be taken up by our enthusiastic designers and architects. It would be desirable if funding for research of new, more cost-effec­tive materials and technologies is secured and buildings already complete and in use at this standard should be monitored.

The point where every new building and renovation is a certified passive house may never become a reality, however it is not the attainment of certification that's important but the aspiration to go as far as is practical within the limitations of each project. It is therefore vital to accept no less than ultra low energy buildings in an attempt to make our entire building stock practically passive house standard; this would put into practice now what building regulations will eventually catch up with in the future.

Paul McAlister