Water management in walls with direct-fixed claddings

Abstract

This research examines the extent to which drainage and ventilation drying can remove water that has leaked through claddings on walls with no specific drainage cavity. Drainage and drying rates were measured in 18 walls with claddings direct-fixed to the timber frame. The goal was to allocate risk scores to different types of direct-fixed claddings that are consistent with the risk matrix that guides the selection of claddings in the New Zealand Building Code. Drainage performance was measured by introducing a controlled water leak and recording the quantities of water draining back outside or reaching the framing, insulation and cladding. Where a wall underlay was present, it kept the frame and insulation dry, but 40%–80% of the water leak was either absorbed by the cladding or trapped between the underlay and cladding. A subset of walls with no underlay (not uncommon in older houses being retrofitted with insulation) was used to investigate different options for maintaining some drainage when insulation was retrofitted. In these walls, pans of wall underlay and drainage mats were found to keep a drainage path open and protected the insulation but were unable to prevent water reaching the frame. Drying rates from the back of the cladding were also measured and compared with evaporative drying rates calculated from climate information and infiltration behind the cladding. A companion article provides ventilation rate data measured using a tracer gas to calculate ventilation drying rates, which were found to contribute significantly more to water management in weatherboard walls than in walls with barrier-type sheet claddings. In fact, ventilation drying behind weatherboard claddings was found to be of a similar magnitude to previously measured drying rates in vented cavity walls.