Impacts of an innovative construction method on internal conditions

Abstract

New Zealand houses are known for producing sub-optimal internal thermal conditions and unacceptably high internal relative humidities. These contribute to poor levels of health, mould and can coincide with the decay of structural timber frames. A proposed solution is to provide an alternative structure utilising plywood instead of building paper, a wrap on the internal face of the timber frame and an additional air gap serving as an internal service cavity, followed by the internal lining. The internal wrap is designed to perform as a vapour check to prevent moisture vapour diffusion from inside into the frame and to permit moisture diffusion from outside through the structure to the internal environment.

Two full scale houses had temperatures, dew points and humidity levels monitored over a full season. To avoid different occupant behaviour influencing internal moisture generation and heating patterns, the buildings are monitored in passive, unoccupied conditions.

The test case house for the research incorporated the innovative construction solution. The second, control house was of identical design and location, using standard construction practice. The houses were situated to prevent shading each other, but in close enough proximity to be on identical sites. Results indicated that the calculated internal moisture content profile appeared to be unrelated to the external moisture content as expected in unoccupied conditions. Instead it followed the profile of the changing internal temperature. Whilst the innovative construction appeared to prevent moisture diffusion into the structure in winter and permit it inside in summer this resulted in a generally higher internal relative humidity than the control house.