Communique June 2017
We have noticed a recent mini-spike in claims resulting from internal moisture issues. One of the key requirements of the NZBC E3-Internal Moisture Clause is to safeguard the occupants against illness, injury, or loss of amenity that could result from the accumulation of internal moisture (Clause 3.1 (a)).Architects have normally associated this with careful detailing around the so-called internal ‘wet-areas’ of buildings, such as bathrooms and kitchens.NZBC E3 Clause also asks that buildings be constructed to avoid the likelihood of fungal growth or the accumulation of contaminants on linings or other building elements and damage to building elements caused by the presence of moisture. With modern construction methods and increasing awareness around energy efficiency and air change rates, a prudent architect allows for expert analysis/review of the hygro-thermal performance of their design. This applies to all areas of a building as well as the traditional ‘wet areas’ such as bathrooms and laundries.Architects are expected to design their buildings in such a way that an adequate combination of thermal resistance, ventilation, and space temperature is provided to all habitable spaces where moisture may generate or accumulate. As the design develops, some thermal bridging and associated moisture issues may become apparent and architects are expected to understand and resolve these potential problem areas before they arise.Most internal condensation issues are caused by thermal bridging and then lack of air tightness strategies. Controlling interstitial moisture through ventilation, for example, is a myth as it doesn’t solve the original problem: the moisture shouldn’t be there in the first place.When detailing projects with high diurnal and seasonal temperature swings, architects should specifically consider thermal bridging and hygro-thermal performance.P.S. Hygro-thermal pertains to the movement of heat and moisture through buildings. Computer-based modelling by a reputable engineer offers an accurate prediction of hygro-thermal performance. Hygro-thermal assessments can model virtually any assembly type, including walls, roofs, floors, and even below-grade foundations. This assessment will allow architects to determine moisture content, relative humidity, dew point and temperature at chosen surfaces and depths for each assembly component, and enable design to avoid early degradation and reduced material life.