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The purpose of this paper is to propose a methodology for evaluating the hygrothermal performance of framed wall assemblies based on design limits. This methodology allows designers to evaluate wall assemblies based on their absolute performance rather than relative performance which is typically done for most hygrothermal analysis.

The approach in developing this methodology was to evaluate wall assemblies against three typical design loads (e.g. air leakage, construction moisture, rain penetration) and determine limits in minimum insulation ratio, maximum indoor humidity and maximum rain penetration rates. This analysis was performed at both the field area of the wall and at framing junctions such as window sills.

The findings in this paper shows example design limits for various wall assemblies in heating-dominated climates in North America. Design limits for wall assemblies with moisture membranes of different vapour permeance are provided for both the field area of the wall and at window sills. Discussions about the importance of 2D hygrothermal simulation and performance of vapour permeable sub-sill membranes are also provided.

This framework of hygrothermal analysis will enable designers to make better decisions when designing framed wall assemblies suitable to the local climate and interior specifications for their projects. It will also enable the development of a design tool that will allow designers to visually see the implications of certain design decisions and filter out designs that do not meet their design conditions.