Moisture in New Zealand Bathrooms - Analysing Moisture Events

A literature review was carried out on the impact of moisture in New Zealand homes as well as the role ventilation and occupant behaviour play in controlling this. Bathrooms in residential homes were identified as being especially vulnerable. NZS4303:1990, clause G4 Ventilation of the New Zealand Building Code, and clause E3 of the New Zealand Building Code were summarised to provide context for how New Zealand buildings are designed. Measurements taken in houses throughout New Zealand by BRANZ as part of the House Condition Survey were made available for analysis. This included measurements of relative humidity and temperature. Data from one Dunedin house was thoroughly explored. This involved three objectives. The first step focused on identifying periods of rapid change in the amount of moisture introduced to the indoor environment, measured in absolute humidity. These periods were named 'moisture events'. The second objective was to visually communicate the changes in temperature and absolute humidity taking place on individual days, highlighting moisture events. The third objective was to analyse the identified moisture events, finding the key areas to focus on for the full analysis as well as areas that could be explored in further research. This process was then applied to all remaining houses. Moisture events were grouped into four categories: increases, decreases, episodes, and combinations. Episodes were the focus of the analysis, representing moisture being actively introduced to the indoor environment and then removed. These categories were further filtered, identifying the moisture events were most likely to have had a large impact on the indoor environment. Days were broken into four hour periods, with the filtered moisture events taking place in each period recorded. These were used to identify patterns in moisture events for each house. If a certain pattern of moisture events frequently took place, then days containing that pattern were described as a 'typical day' for that house. The mean and median absolute humidity at the start, peak, and end of the unfiltered episodes from each house were then calculated. The mean and median episode length was also calculated. The results were compared to the Household Energy End-use Project (HEEP) and to the typical days for each house. The results were grouped according to factors such as the number of bathrooms in the house, the floor area, the house location, and the event length. The number of bathrooms present in the house was found to have a large impact on the size and frequency of moisture events. As expected, larger bathrooms recorded lower increases in absolute humidity from the start to the peak of episodes. Rooms with a greater volume would require more moisture to reach the same number of grams of water per cubic metre. However, the smallest bathrooms also recorded low increases in absolute humidity.