This paper describes the guidelines prepared by NIST for GSA. These guidelines are organised by envelope construction system and contain practical information on the avoidance of thermal performance problems such as thermal bridging, insulating system defects, moisture migration problems, and excessive envelope air leakage. For each envelope system, both good and bad practice are discussed with an emphasis on the graphical presentation of envelope design details.
There are several methods by which the airtightness of a building can be measured. One method involves the use of a fan to pressurize or depressurize the building. This creates a known pressure difference across the building envelope. Thecorresponding air flow through the fan is measured and this is an indication of the airtightness of the building. This air flow rate can be expressed as the number of building air changes per hour, a useful unit when comparing buildings of different volumes. So far only simple methods have been employed to analyse this condition.
An appropriate way to identify the most efficient ventilation systems and improve their design is to use design codes for ventilation rates. These rates are strongly influenced by spatial and temporal fluctuations in wind pressure on the facade and roof. The influence of the effects of wind on ventilation was studied using a model which includes air compressibility, together with the pressure field measured on a model in a boundary layer wind tunnel. The simulation results obtained are analyzed using a design code.
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