A survey of airtightness and ventilation rates in post 1994 NZ homes

The airtightness of 36 houses built since 1995 and across four cities in New Zealand (NZ) was measured. In a subset of 31 of these homes, the average ventilation rate was measured over several weeks in the winter using a perfluorocarbon tracer technique (PFT). These results can be added to earlier airtightness data to provide a platform for improving the air quality and energy efficiency of residential ventilation in NZ.
Earlier airtightness data from the mid 1990’s showed a trend for newer houses to be more airtight than older houses, largely as a result of sheet lining materials replacing strip flooring and the development of more airtight joinery. This trend continued in this study, even though there are no airtightness requirements for houses in New Zealand. The average N50 result for houses built since 1995 was 6.7 air changes/hour (ACH), down from 8.5 ACH for houses built in the previous decade.
Most new houses meet NZ building code requirements for ventilation (window and door openings that exceed 5% of the floor area), but the PFT measurements showed that most houses struggled to reach recommended levels of ventilation (0.35-0.5 ACH during the winter) because the windows weren’t open often enough.
In recent years it has become common for occupants to add additional supply-only ventilation to control moisture. Houses with operational supply-only ventilation systems generally had more than enough ventilation but there were several cases where the ventilation system had been turned off.
There was clear evidence of moisture problems in several of the more poorly ventilated houses.