1.1 DESCRIPTION OF THE GUIDELINES
The purpose of these guidelines is to provide practical design and construction information directed
towards achieving good thermal envelope performance through the avoidance of thermal defects. It
is assumed that the designer has already chosen the envelope system and will use the guidelines
as a source of information on design and construction issues key to thermal performance.
The guidelines are concerned primarily with conductive heat transfer, air leakage and airborne
moisture transport through the building envelope. The guidelines do not cover the many other
issues important to the thermal envelope performance such as appropriate levels of thermal
insulation, daylighting and other glazing system issues, thermal mass effects, design methodology,
thermal load calculations, and interactions between the envelope and HVAC equipment. The
control of heat, air and moisture transfer constitutes only a portion of the performance requirements
of building envelopes, and obviously the envelope design must address all of the varied
requirements. Some of these other envelope design issues include structural performance,
aesthetics, fire safety, lighting and rain penetration.
The guidelines present many design details that lead to thermal defects, along with improved
alternatives. The alternative details have been selected based on their being practically
constructable and having a demonstrated record of performance. Suggested fixes that do not have
a well-established record of performance are intentionally omitted, though they may turn out to
provide acceptable performance.
The guidelines are organized into three sections: principles, design and systems. Each section
consists of a series of stand-alone "fact sheets" addressing a specific issue or system. The first
section, principles, provides background information on thermal envelope performance including a
discussion of thermal defects and their potential consequences. The material in this section is not
necessary for the user, but does provide useful background information and describes the
motivation and bases for the guidelines. The second section, design, contains fact sheets on basic
design principles for achieving good thermal performance and avoiding thermal envelope defects.
The material in this section describes air barriers, vapor retarders and thermal insulation,
specifically addressing the design features of each that are essential to envelope thermal integrity.
This section also contains a discussion on the control of rain penetration. The third section,
systems, constitutes the substance of the guidelines. This section contains fact sheets on particular
envelope systems, each one describing those design features that are crucial to achieving good