NISTIR 4821 Envelope Design Guidelines for Federal Office Buildings: Thermal Integrity and Airtightness  

Date: 
03-01-1993

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.

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