FEMA P55 Coastal Construction Manual, Fourth Edition - Mad Cad

11 Designing the builDing envelope Volume II
Figure 11-52.
Blow-off of one of the
nailers (dashed line on
roof) caused panels
to progressively fail;
cantilevered condenser
platform (arrow);
broken window (circle).
Estimated wind speed:
130 mph. Hurricane
Katrina (Louisiana, 2005)
11.5.5.2 Hail
Several metal panel and shingle systems have passed UL 2218. Although metal systems have passed Class 4
(the class with the greatest impact resistance), they often are severely dented by the testing. Although they
may still be efective in inhibiting water entry, the dents can be aesthetically objectionable. Te appearance
of the system is not included in the UL 2218 evaluation criteria.
11.5.6 Slate
Some fber-cement and tile products are marketed as “slate,” but slate is a natural material. Quality slate ofers
very long life. However, long-life fasteners and underlayment are necessary to achieve roof system longevity.
11.5.6.1 High Winds
Because of limited market share of slate in areas where research has been conducted after high-wind events,
few data are available on its wind performance. However, as shown in Figure 11-53, wind damage can occur.
Methods to calculate uplift loads and evaluate load resistance for slate have not been incorporated into
the IBC or IRC. Manufacturers have not conducted research to determine a suitable pressure coefcient.
Demonstrating slate’s compliance with ASCE 7 will be problematic until a coefcient has been developed. A
consensus test method for uplift resistance has not been developed for slate.
In extreme high-wind areas, mechanical attachment near the nose of the slate should be specifed in perimeter
and corner zones and perhaps in the feld. Because this prescriptive attachment suggestion is based on limited
information, the uplift resistance that it provides is unknown.
11-46 COASTAL CONSTRUCTION MANUAL