Thermal bridges of modern windows – experience with minimum acceptable surface temperature

Description

A ventilated cavity behind the cladding of timber frame walls is often considered good building practice that facilitates the removal of moisture from the construction. However, moisture will only be removed from the construction by ventilating it with dry air, whereas ventilating with humid air might add moisture to the construction.

Full-size wall elements with wooden cladding placed in a test building were exposed to natural climate on the outside and to a humid indoor climate on the inside. Temperature and moisture conditions inside the wall elements and climate parameters were monitored. Test parameters included cavity/unventilated cavity/no cavity, cavity size, vent geometry, type of cladding and type of wind barrier.

The potential durability of the wooden façade claddings was evaluated by coupling the measured time series of moisture content, temperature and time by means of a model for mould growth on wood-based materials.

The paper presents results from the investigation with emphasis on a discussion of the effect of cavity ventilation on moisture content in timber frame walls. In terms of moisture content behind the wind barrier, the behaviour of wood frame walls with a non-ventilated cavity was found not to be inferior to the behaviour of wood frame walls with a ventilated cavity.