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Feedback from the 2018 AIVC Workshop in Wellington

06-09-2018 | New Zealand

The 2018 AIVC workshop was held in Wellington, New Zealand on 19-20 March. The theme of the workshop was how airtightness and ventilation can contribute to better buildings. The workshop brought together researchers, policy makers, designers and practitioners.

Historically, NZ homes have had a rudimentary approach to both airtightness and ventilation. In contrast, many European countries have airtightness and ventilation targets entrenched in their codes and regulations – largely driven by EU wide energy directives. The workshop was a chance for the NZ audience to learn from experiences from overseas and discuss what might be a practical way forward for New Zealand.

The following bullet points are a selected summary of the workshop:

  • The poor condition of the NZ housing stock was discussed to help put the NZ situation into context for the overseas researchers

Approximate figures from the most recent BRANZ house condition survey show:

  • 50% of houses need more insulation in the ceiling or floor.
  • 50% of people do no heat their bedrooms in winter, leading to startlingly low temperatures.
  • 50% of houses don’t even have basic extract ventilation in the bathroom or kitchen.
  • 50% of houses have visible mould inside, due to a lack of adequate insulation, heating and ventilation.
  • The health costs associated with indoor air quality are now becoming known and are a stronger argument for improved airtightness and ventilation control

Overseas, airtightness requirements were founded on energy saving principles. However, from an energy standpoint, NZ houses only contribute 8% of the countries carbon emissions (In Germany, for example, this changes to 28%), and much of our electricity comes from renewable sources - if anything we should be using more energy to heat our homes up a bit! From a health standpoint, about 1600 people die each year from conditions attributable to poor housing in NZ.

  • If the building code were to include an airtightness requirement, it need not be a step change from current construction practice. However, many older homes would benefit from an airtightness upgrade.

BRANZ data shows that most new houses are now at an airtightness level that is comparable with countries with similar climates. There was some discussion as to whether we should be aiming for ultratight houses. Researchers from the US suggest that this is not worth doing because, in our relatively mild climate, the energy savings are simply not worth the effort. For US climates with similar heating requirements, net-zero energy houses are common, but these are built to an airtightness level similar to a typical new NZ house; They could build more airtight houses, but it is easier to simply add more solar panels to achieve the necessary energy savings. In colder parts of NZ, it might be justified tightening the envelope slightly, but it would not be a massive shift from current practice.

For the older houses, it would be sensible to perform draft stopping as part of any insulation upgrade, because many of the older uninsulated houses will be excessively ‘air loose’, based on measurements by BRANZ and others.

  • Ventilation requirements do need a rethink. 100% of the attendees thought the acceptable code solution of relying on openable windows was inadequate.

Along with the lack of heating New Zealanders use in the home, a lack of ventilation causes a number of moisture related problems. The New Zealand building code stipulates that openable windows are an acceptable ventilation solution if the window size is 5% of the rooms floor area.

In the newer, reasonably airtight and well insulated homes, we know that occupants don’t open their windows enough. Japan experienced similar problems and ended up introducing requirements for 24hr mechanical ventilation. In the US, the situation is also similar but there the focus appears to be on encouraging use of mechanical systems by the occupant. At the very least, the workshop attendees thought that ventilation provided by mechanical systems should be performance verified either by the installer or a third party as part of the commissioning process.