BUILDING DESIGN FEATURES AND PRACTICES
Introduction. This section contains information on design features
and practices affecting natural ventilation in buildings. Guidelines based on
the best available data are provided. Conflicts between differing guidelines
will arise in some cases. Resolution of these conflicts is left to the
designer's discretion, since each must be handled on a case-by-case basis.
Comfort, life-cycle costs, maintenance concerns and functional efficiency
should be the primary criteria for such decisions, and designers should draw
on their previous experience as well as on the guidelines presented here. In
most cases, there are several alternative approaches to achieving a desired
Site Selection and Planning
impacts on the comfort of the building's occupants and on the functioning of
the building and its systems. In fact, the feasibility of using natural
ventilation for cooling may depend on proper siting. Consideration of the
wind and thermal implications of site planning and selection must be given the
highest priority for any building project in the earliest stages of the
planning and design process.
The first task of the planner or designer is to identify the most
suitable site for the building(s) to take advantage of the favorable, and to
mitigate the adverse, characteristics of the site and its microclimate. For
buildings using natural ventilation, this includes avoiding enclosed valleys
and sheltered locations, maintaining adequate building spacing (avoiding wind
shadows and wakes) and organizing the site layout to increase interior air
velocities and minimize interior heat gain.
Design of the buildings should not only be related to conditions in
the building interior, but also to the external spaces between and around
them. Comfortable outdoor spaces can provide valuable additional or
alternative living area in many types of projects.
Ventilative Considerations. The major site factors affecting
ventilation are described in paras. 184.108.40.206 through 220.127.116.11. Figure 6 is a
flowchart for design and analysis of factors.
Topographic Features. If maximum ventilation is desired, avoid
enclosed valleys and very sheltered locations. Sites near the crest of hills
or ridges may provide increased exposure to winds for ventilation. Ridge
crests can receive wind speeds higher than those on flat ground; an increase
of 20 percent is an average rule of thumb. In very windy locations, sites at
the crest of hills or mountains may recieve too much wind with potential for
problems with structure and driving rain. Appendix A, Section 2 discusses
airflow around such features as hills and valleys.
If continuous ventilation is desired, sites on or near the top of a
slope (for increased wind exposure), and facing south (to southeast for
decreased afternoon solar exposure) are recommended. If night ventilation is
desired, recommended sites are those near the bottom of a slope (to catch the