Ventilating Wall Cavities Above Windows

Abstract

This paper shows that the cavities above two-part head flashings can be designed to borrow ventilation from cavities flanking the window through vented battens. It is part of a program of research designed to extend the range of flashing options for windows used in temperate New Zealand. Ventilation rates are measured in the cavities above window heads with a constant and uniform emission tracer method. These are similar to ventilation rates calculated from wind and stack pressures at openings representing engineered vents and infiltration paths into the head cavities. The leakage characteristics of these openings are measured with a pressurization technique, and together with temperature and wind data, formed the data set used to calculate equivalent cavity ventilation rates. As with earlier studies of ventilation in water-managed cavities, infiltration turned out to be an important source of cavity ventilation. Turning off the infiltration paths (possible in the numerical model) shows that the vented batten solution is ultimately less dependent on infiltration than the traditional head flashing ventilated case, and that ventilation through vented battens can be engineered to replace ventilation over the head flashing.