Field Study of Relationships Between Indoor Thermal Conditions and Two Major Causes of Allergies—Dust Mites and Mould—In New Zealand Houses

Based on field studies, this study contributes the new physical data of winter indoor thermal conditions of the indoor spaces with four different dust mite allergen levels in New Zealand houses. This study provides a new method to identify the relationships between indoor thermal conditions and indoor dust mite allergen levels. This study found that the indoor mean relative humidity (RH) close to the floor must be controlled below 70%, and there must be less than 30% of time in winter when indoor RH close to the floor is higher than or equal to 75% to maintain indoor dust mite allergens at an undetectable level; and the indoor mean RH close to the floor must be controlled below 75%, and there must be less than 50% of time in winter when indoor RH close to the floor is higher than or equal to 75% to maintain indoor dust mite allergens at a low (acceptable) level. This study also identified the relationship between indoor thermal conditions for dust mites to thrive and for mould spores to germinate. This study provides a strategy or guideline for preventing indoor allergies related to dust mites and mould under the temperate climate zone; the winter is mild and humid.