Performance Evaluation of Proprietary Drainage Components and Sheathing Membranes when Subjected to Climate Loads

Objective

To develop appropriate design guidelines and appropriate use of membranes and drainage components in selected wall assemblies for specified climate zones based on their drainage and drying potential.

Background

The issue of drainage of cavities behind cladding is important because lack of drainage may cause water to be entrapped in these interstitial spaces. The entrapment of moisture cannot be adequately managed by drying alone, and may result in conditions that are detrimental to the long-term performance of the wall system. In wood-frame walls it may lead to premature deterioration due to the formation of wood rot or mould in the wall components, and in both wood frame and steel framed assemblies moisture in the wall may lead to a heightened risk of corrosion of metal ties, connectors or assemblies. In either case, it may also bring about an increase in the moisture content of interior wall components and hence reduced thermal performance and increased energy costs. It is therefore necessary to investigate the suitable combinations of drainage components and sheathing membrane given specific types of wall configurations that will not succumb to moisture retention in the interstitial spaces behind the cladding, and the climates in which these combinations could be recommended. The body of evidence obtained from results of performance evaluation tests on these proprietary products is also a prerequisite for establishing compliance to the building code.

Drainage and retention of water by cladding systems have been studied. However, such studies have focused exclusively on wood-frame wall assemblies, and no thorough consideration has yet been given to the effects of natural, combined and forced convection brought about by temperature differences and wind pressure across the wall. With respect to drying, most of these studies have focused on characterization of the air flow in ventilated cavities of rain screen wall systems, measuring the ventilation rates in wall cavities and the modelling of convective drying of ventilated wall cavities in building enclosures. Such studies have not as yet been extended to permit determining selection criteria for appropriate combinations of proprietary drainage components and sheathing membrane, or the appropriate depth of the cavity behind the cladding for given building heights and specific geographic locations.

The project proposed by NRC-IRC would focus on developing the necessary performance evaluation procedures on the basis of hygrothermal simulations of wall systems comprised of selected combinations of components and subjected to various climate loads. NRC-IRC's recently developed hygIRC-C multi-physics hygrothermal software will be used for simulations, thus allowing for detailed analysis of the different test and performance evaluation scenarios. The simulations would follow from information derived from; (1) laboratory testing to determine the basic hygrothermal properties of individual components and, (2) full-scale testing of assemblies to reproduce drainage and drying conditions sufficient to characterize the different combinations of membrane, drainage media and vented space. Full-scale testing would be performed on a novel test facility configured to monitor specimen weight change over time, which would thus track the affect of wetting and drying of the test specimen.

Expected Outcomes

• Performance evaluation of WRB's, sheathing membranes and drainage components performed through hygrothermal; simulations benchmarked to laboratory testing that would:
• Determine drying potential of wall assemblies (wood or steel frame), leading to a better understanding of the capacity of various wall systems to drain and dry when wall systems are:
  • Configured with different claddings (e.g. brick, stucco, stone masonry veneer), or with other components (e.g. combinations of sheathing membrane, drainage components, including those of the project participants), and
  • Placed in different climates and subjected to extreme conditions of wind-driven rain.
• Apply knowledge acquired to the development of test methods and a guide to evaluations for use in Canada and the US.

Partners

ABAA (Air Barrier Association of American) / NRC-IRC (Institute for Research in Construction)

The main benefit to the partners joining this project will be obtaining firsthand knowledge of the moisture management and dissipation performance of wall systems configured with their products that incorporate different combinations of cladding, sheathing membrane and drainage systems. Such knowledge will permit partners to understand the consequences of combining specific components on the moisture management capabilities of the wall systems. It will also permit suggesting appropriate choices for moisture management components in respect to a particular wall system and the climate in which it is expected to perform. Knowledge and expertise contributed by the partners will also provide highly useful input to the development of evaluation guides and acceptance criteria of such products and systems. It is intended that any test procedures developed in the project would provide the basis of a testing and evaluation protocol for a product evaluation guide forming part of an approvals process.

Start/Expected Completion Dates

This project is expected to begin in May 2010 and will be completed in 2012.

Project Managers

Michael A. Lacasse, Ph. D. (IRC-CNRC)
M. Laverne Dalgleish (ABAA Industry representative)

Related Information

Institutes:

• NRC Institute for Research in Construction