Page 57 - Build 151

New homes dripping
Modern building practices often result in more airtight dwellings. BRANZ looked at two new builds with internal moisture problems and found issues could have been avoided with e cient ventilation.
BY IAN COX-SMITH, BRANZ BUILDING PHYSICIST
As well as displaying similar symptoms of water running down the windows, both buildings had virtually the same set of ventilation issues. The major di erence was that the spacious 4-bedroom house had plenty of openable windows (although these weren’t opened often), whereas the 60 m2 apartments had only one or two openable windows and smaller air volume per person.
Less air in ltration in new homes
In both cases, the airtightness measure- ments were as expected for new construc- tion with no additional airtightness construction practices incorporated other than those inherent in modern house building methods.
Modern construction tolerances generally mean much less air in ltration compared with houses from the 1980s and earlier. The air change rate that results from the measure- ment of airtightness does not represent the air in ltration rate that occurs in practice. Typically, it represents a worst-case
Internal moisture
Disconnected duct in the apartment ceiling.
LAST WINTER, BRANZ was contacted by two building owners who were nding it di cult to control the internal moisture in their properties. One was a single-level standalone 4-bedroom house, and the other was a 2-storey block of single-bedroom apartments.
In both instances, the buildings were less than a year old, and despite having double glazing, they were experiencing an almost continuous layer of condensation on the
window framing and the glass (see cover). The occupants were having to mop up moisture on the window sills daily and were nding some mould growth on walls and ceilings.
Double-glazed but wet windows
BRANZ scientists were given the oppor- tunity to measure the airtightness of the buildings and to monitor the temperatures and relative humidity to help understand what might be causing the moisture issues.
Build 151 — December 2015/January 2016 — 55
FEATURE SECTION