Page 49 - Build 151

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OLDER HOUSES
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AIR LEAKY
and timber windows to sheet materials and aluminium joinery with seals.
The current trend is because of the drive for more energy-e cient buildings, improved levels of indoor nish, such as square stopping and an increase in slab-on- ground construction.
Building Code relies on open windows
This trend to more airtight homes has affected infiltration rates. The question now is whether or not clause G4 needs to be updated to re ect this.
Currently, the most common route to demonstrate compliance with clause G4 is the provision of 5% of the building oor area as openable windows. This assumes that occupants open the windows regularly. Older houses probably OK
In older housing, the guidance in clause G4 is likely to be su cient, but the ventilation survey undertaken during WAVE indicated that the level of window opening by occu- pants varies.
Newer houses short on ventilation
If occupants in newer housing do not open windows, this can cause problems.
Actual ventilation rates measured in conjunction with the survey found that about a third of the sample occupants were getting insu cient ventilation.
The measured ventilation rates in these cases was very close to the estimated in ltra- tion rates from blower door tests, which indicated windows were not being opened that often (see pages 55–56).
Study checking window use
This has resulted in the BRANZ occupant behaviour project, where new sensor tech- nology will enable measurements of how often and how far occupants are opening their windows and doors.
This project will give important information on how people are using their homes.
Internal moisture
1950s
1960s 1970s 1980s
1990s 2000s
Figure 1: Increasing airtightness of newer New Zealand homes.
In BRANZ case studies, sta have seen the consequences of high indoor moisture levels from venting a dryer into a living space. One case assumed that a small extractor fan would remove the moisture, but once the moist dryer air mixed with the air in the house, it was di cult to extract.
The recommended solution is to vent the dryer directly outdoors. This requires thought at the design stage as it is sometimes di cult to do after the build is completed.
What is ventilation?
Ventilation consists of:
● backgroundin ltration
● purpose-designed ventilation achieved by
mechanical or passive means.
Background infiltration
In ltration is the uncontrolled air move- ment through gaps and openings in the building envelope. It is typically driven by wind and stack pressure differences between indoors and outdoors.
There is much debate as to the quality of in ltration air, which is dependent on where it is coming from. Air from sub oors can be a concern, with typically high moisture levels.
Roof-space air can have potential moisture and airborne particle issues.
Infiltration air can also have energy impacts – the magnitude of this varies with airtightness and the nature of the ow paths in the building envelope.
Mechanical and passive ventilation
Ventilation can be provided by:
● opening windows
● passive vents
● mechanical extraction, such as a range-
hood and bathroom fans
● mechanical supply
● balanced mechanical
● passive stack ventilators.
To be compliant with Building Code clause G4 Ventilation, ventilation air must come from outside the building.
Increasing airtightness having an impact
Work in the BRANZ WAVE (Weather- tightness, Air quality and Ventilation Engineering) programme highlighted a trend to more airtight construction (see Figure 1).
Earlier trends in increasing airtightness resulted from a shift away from strip ooring
Build 151 — December 2015/January 2016 — 47
FEATURE SECTION
Average airtightness (air changes per hour @ 50 Pa)