FEMA P55 Coastal Construction Manual, Fourth Edition - Mad Cad

11 Designing the builDing envelope Volume II
performance of the building envelope is also necessary. Good building envelope performance is critical for
buildings exposed to high winds and wildfre.
Good performance depends on good design, materials, installation, maintenance, and repair. A signifcant
shortcoming in any of these fve elements could jeopardize the performance of the building. Good design,
however, is the key element to achieving good performance. Good design can compensate to some extent for
inadequacies in the other elements, but the other elements frequently cannot compensate for inadequacies
in design.
Te predominant cause of damage to buildings and their contents during high-wind events has been shown to
be breaching of the building envelope, as shown in Figure 11-1, and subsequent water infltration. Breaching
includes catastrophic failure (e.g., loss of the roof covering or windows) and is often followed by wind-driven
water infltration through small openings at doors, windows, and walls. Te loss of roof and wall coverings
and softs on the house in Figure 11-1 resulted in signifcant interior water damage. Recommendations for
avoiding breaching are provided in this chapter.
For buildings that are in a Special Wind Region (see Figure 3-7) or in an area where the basic (design) wind
speed is greater than 115 mph, 2 it is particularly important to consider the building envelope design and
construction recommendations in this chapter in order to avoid wind and wind-driven water damage. In
wind-borne debris regions (as defned in ASCE 7), building envelope elements from damaged buildings are
often the predominant source of wind-borne debris. Te wall shown in Figure 11-2 has numerous windborne
debris scars. Asphalt shingles from nearby residences were the primary source of debris. Following the
design and construction recommendations in this chapter will minimize the generation of wind-borne debris
from residences.
Figure 11-1.
Good structural system
performance but
the loss of shingles,
underlayment, siding,
housewrap, and soffts
resulted in signifcant
interior water damage.
Estimated wind speed:
125 mph. 3 Hurricane
Katrina (Louisiana, 2005)
2 The 115-mph basic wind speed is based on ASCE 7-10, Risk Category II buildings. If ASCE 7-05, or an earlier version is used, the
equivalent wind speed trigger is 90 mph.
3 The estimated wind speeds given in this chapter are for a 3-second gust at a 33-foot elevation for Exposure C (as defned in
ASCE 7).Most of the buildings for which estimated speeds are given in this chapter are located in Exposure B, and some are in
Exposure D. For buildings in Exposure B, the actual wind speed is less than the wind speed for Exposure C conditions. For example,
a 130-mph Exposure C speed is equivalent to 110 mph in Exposure B.
11-2 COASTAL CONSTRUCTION MANUAL