MIL-HDBK-1011/2
allow cooler air that has passed over the body of water to enter the building
from below. Elevating the building may also be worthwhile if the ground is
continually damp or when the building is located in a flood plain.
Airflow beneath a highrise elevated building may be accelerated
beyond a level which is comfortable or safe for pedestrians. Refer to
Appendix A, para. 3.3.3.
4.5
Building Envelope and Structure
4.5.1
General Principles. The building materials and type of
construction used will have a significant effect on the heat gain and heat
loss characteristics of the building. For naturally ventilated buildings,
lightweight materials with light-colored, heat-reflecting outer surfaces are
desirable. The major building components of the structure are the roof, which
provides shade and protection from the rain, and the fenestration system,
which determines the volume, velocity and distribution of interior
ventilation.
4.5.2
Roof and Roof Ventilators
[retrieve figure]
4.5.2.1
Roof Overhang Effects on Room Ventilation. Roof overhangs
can enhance ventilation by damming the airstream in a pocket at the
wall thereby increasing the positive pressure outside the window and
consequently the airflow through the opening (see Figure 19).
Figure 19
Roof Overhand and Room Ventilation
4.5.2.2
Roofs--Thermal
Considerations. Roofs receive the most solar radiation of any building
surface and are the primary protection from direct radiation in low-rise
buildings. The amount of solar radiation falling on the surfaces of a
building varies with latitude, season, time of day and building
orientation. Figure 19 shows the relative solar intensities throughout the
day for each building surface for 26MN. latitude for each season.
Use light coloring on the roof to reflect solar gain. Effective
insulation, including the use of radiant barriers above resistive insulation,
is critical to ensure comfort in spaces below the roof (see Figure 21).
Attics above living spaces need to be independently ventilated. As roof pitch
decreases, the temperature of the ceiling below can be expected to rise.
Also, ventilation of the attic space becomes progressively more difficult.
Attic ventilation
should be designed so that openings are provided in both positive and negative
pressure areas to provide proper cross-ventilation. Refer to Appendix A,
Section 3.) When venting attic spaces, be careful to place exhause outlets so
that hot air is not
blown into occupied spaces or near air inlets.
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