b'TECHNICAL ARTICLEAN EXPERIMENTAL STUDY:Hygrothermal performance of vented and ventilated wall systemsBy Fitsum Tariku, BCITT his is a two-part article; in this first part, experimental measure-ment results on cavity ventilation, hygrothermal and thermal performances of wood frame wall systems with different flashing design are presented. In the second partto appear in a future issue of Elementsa model for estimating cavity ventilation in ventilated wall systems will be presented based on experimental measurements.Since the mid-1990s, adding an air gap behind an exterior cladding has become common practice to enhance the hygro-thermal performance of wall assemblies in climate zones with high rain load. Tenwolde et al. (1995) and Lstiburek (1999) state that all wood-frame wall assemblies require a drainage space for locations in North America that receive more than 500 mm of rain annually. Some building codes, such as the National Building Code of Canada (2015) and British Columbia Building Code, require 10 mm minimum air gap behind a cladding in climates with a high moisture index. Other building codes require a means of draining water without specifying what the minimum air gap should be (Interna-tional Building Code 2018).In such wall systems, which are normally referred to as rain-screen wall assemblies, the air gap will act as a capillary break,FIGURE 1: TEST PANELS CROSS-SECTIONS AND FLASHING DESIGNS CONSIDERED IN THE STUDYA) which in effect not only reduces (orCONVENTIONAL WALL (WALL WITH NO AIR GAP); B) VENTED WALL DESIGN; C) VENTILATED WALL DESIGN.eliminates) liquid moisture transfer but also limits the vapour diffusion and convective moisture exchange between cladding and sheathing to the moisture storage capacity of the air in the air gap. The air gap also allowsments on cavity ventilation at BCIT and thematerials used to construct the test panels air to move through, transporting heat andimpact of cavity ventilation on the thermalare shown in Figure 1. Figure 1a represents moisture into and out of the cavity. Althoughand moisture performance of rain-screena conventional wall system: a wall with the function and benefit of a capillarywall systems are shared.on-air gap between the sheathing board and break has been demonstrated in severalcladding. The other two wall systems have publications, the relative contribution ofFor the study, three test panels with differentthe same air gap width but different top cavity ventilation (airflow) in the moistureair cavities and top flashing designs wereflashing designs, intended to create a vented management of wood-frame wall systems ismanufactured, instrumented and installed(Figure 1b) and a ventilated (Figure 1c) wall not clear. In this article, results are obtainedside-by-side on the BCIT Building Envelopesystem. In the ventilated wall system, the from long-term filed experimental measure- Test Facility (BETF). The configuration andclearance between the cladding exterior 14 BCBEC ELEMENTSA BCBEC PUBLICATION'