Wind Damage >> How Long Do Hurricanes Last

The most critical aspect of building in hurricane hazard areas is the method of connecting the structural members. Pilkey et al. (1981) note that wood is one of the best materials for absorbing short-duration loads such as those caused by wind, but the strength of wood cannot be used to advantage if the How Long Do Hurricanes Last members are not adequately attached to one another. 

Construction in hurricane hazard areas must differ from construction in less hazardous areas. In conventional construction, buildings are designed to support primarily vertical loads: the weight of the building, its contents, and inhabitants. Under normal conditions, these gravity loads comprise the primary stress applied to the How Long Do Hurricanes Last structure. 

Significant horizontal forces may How Long Do Hurricanes Last be applied to structures in hurricane hazard areas. Pilkey et al. (1981) recommend that structures in hurricane hazard zones be built with the assumption that a horizontal or uplift force of at least 25% of the vertical load on a structural member may be applied to the structure during a hurricane. 

The key for enabling the structure to resist these loads is to adequately How Long Do Hurricanes Last connect, or anchor, each element of the structure to the adjacent element. FEMA (1986) notes that an anchorage system should adhere to the following criteria: 1. withstands all anticipated forces without structural failure; 

2. continues to perform satisfactorily when materials are wet, as well as under wetting and drying conditions; 3. is protected to withstand How Long Do Hurricanes Last corrosive conditions without loss of strength for many years, preferably for the lifetime of the building; 4. is readily available and requires only normal carpentry for installation. 

Connectors must be properly selected according to application, adequate in size and number, and properly attached. Wolfe et al. (1994) conclude that the extent of the damage resulting from Hurricane Andrew was not due to any inherent weakness in wood-frame buildings, How Long Do Hurricanes Last but was due in part to misapplied connections. 

Manning and Nichols (1991) concluded after examining damage from How Long Do Hurricanes Last Hurricane Hugo that most of the roof damage was due to the failure of connectors that were inadequately sized. Improper connections were the cause of most roof failures during Hurricane Alicia (1983) as well. 

Wall failures during Alicia were attributed to inadequate connections between roofs and walls, and between walls and floor plate, deck, and floor joists (AIRAC, 1989). Simple nailing, especially toenailing, How Long Do Hurricanes Last is not adequate in hurricane hazard areas. Bolts, lag bolts, or nails at right angles to the direction of force provide the greatest factor of safety. 

Lag bolts offer a significant advantage over nails. According to Issa et al. (1994) the smallest lag bolt has more that four times the withdrawal How Long Do Hurricanes Last resistance of the largest nail. Toenailing provides an especially weak connection because of the tendency of the nail to split the wood in the toenailed member (Pilkey et al., 1981). 

Roof-to-wall connections are the most important. This is not only because of the large uplift forces that may be at work on the roof, but also because the number of connections is limited to the number of roof rafters or trusses in the system. At lower levels in the structure, How Long Do Hurricanes Last the number of possible connections is greater. 

For example, in wall construction, nailed plywood sheathing can be used to supplement strap connections between roof and wall, and How Long Do Hurricanes Last wall and sill plate. Galvanized connectors, also called "hurricane straps," are the most common connectors used in hurricane hazard areas. 

The straps come in a variety of shapes, but typically connect the rafter or truss to the top plate or wall stud. The strength of hurricane straps lies in the fact that the nails used to hold the strap in place are always at right angles to the wood members to which they are attached. Wall-to-foundation How Long Do Hurricanes Last connections transfer uplift forces on the roof downward to the foundation. 

Plywood sheathing can act as an effective connector. It is important that the sheathing be nailed into the top plate of the wall, and How Long Do Hurricanes Last to the floor joists at the bottom. 

If the sheathing is only nailed to the bottom plate, the connection will be inadequate because the nails that hold the bottom plate to the floor joists lie in the same plane as the uplift forces that must be resisted; How Long Do Hurricanes Last the bottom plate may simply pull off. 

This connection's strength depends on the number of nails used (FEMA, 1986). North Carolina coastal building standards, designed for building survival in 120 mph winds, How Long Do Hurricanes Last provide a good example to follow for connecting roofs to foundations. 

According to AIRAC (1989), the standards require that 1. every other rafter be tied to the ceiling joist and studs with a metal tie; 2. rafters be braced with collar beams and horizontal braces to ceiling joist; and 3. secure connections using a combination of wind anchors, How Long Do Hurricanes Last plywood or steel rods be provided from the rafters down through the floor joists or beams. 

4. Connectors made of metal are the most commonly used. However, in coastal areas this presents a problem. Coastal areas have a highly corrosive atmospheric environment, How Long Do Hurricanes Last because of inland transport of salt spray by the wind, combined with generally higher moisture levels in the air. All metal connectors are subject to corrosion over the life of the structure. 

In this environment, the typical life of fabricated metal connectors is five to 10 years (FEMA, 1986). While pre-galvanized connectors work well in protected areas of the structure, galvanized connectors are preferred in exposed parts of the building. Recently, How Long Do Hurricanes Last stainless steel connectors have become available, and offer the greatest protection against corrosion. 

Detailed information on connector selection and application can be found in Standard for Hurricane Resistant Residential Construction (SSTD-10). Preparing a home to withstand hurricane forces is best begun before construction, How Long Do Hurricanes Last when mitigation techniques can be incorporated most economically and effectively . 

However, this does nothing to protect the enormous inventory of existing homes in hurricane hazard areas.The options for improving the storm-worthiness of homes are limited once homes are constructed; nonetheless, How Long Do Hurricanes Last some steps can be taken. 

According to FEMA (1986), additional rigidity and stability of a gable roof framing system can be provided by installing 2x4's on 2-foot centers between the roof rafters or trusses, for about 8 feet at each end of the house. These will not only strengthen the roof, How Long Do Hurricanes Last but will provide additional nailing surface for roof sheathing materials. 

Using construction adhesives in addition to nails when installing roof sheathing will also improve uplift resistance. Cook et al. (1994) suggest that the highest priority for retrofitting is the protection of openings with shutters or How Long Do Hurricanes Last impact resistant glazing. In high wind areas, better attachment of roof sheathing is also important. 

This retrofit is easily accomplished when re-roofing a building. Once old roofing is removed, sheathing can be renailed to a more rigorous schedule, How Long Do Hurricanes Last and a wind-resistant roof covering can be installed. Calfee (1995) goes a step further and recommends removing sheathing at the time a house is re-roofed, and installing hurricane clips. 

Cook et al. (1994) recommend requiring that roof sheathing be renailed as part of the permit process How Long Do Hurricanes Last for re-roofing buildings. The following are potential ways to retrofit: 1. add shutters for glazed openings 2. renail sheathing 3. create a secondary water barrier 4. provide support for sliding glass doors and double doors opening to the outside 

5. improve anchorage of windows to openings 6. add ridge ventilators to reduce uplift of How Long Do Hurricanes Last roof sheathing 7. strengthen garage doors and particularly double-wide garage doors 8. improve connections of porch roofs and overhangs 

9. anchor adjacent structures, including privacy fences, pool enclosures, and How Long Do Hurricanes Last patio roofs Gaus et al. (1993) offer several examples of steps that could be taken by a homeowner to reduce the risk of hurricane damage to the home. It is not possible simply to renail a roof with suspect sheathing to joist or truss connections. 

However, a bead of construction adhesive could be How Long Do Hurricanes Last applied from within the attic with a caulking gun to each side of the roof rafters or trusses to form a connection with the sheathing. This connection, in the opinions of Gaus et al. (1993) would be at least as strong as that provided by common forms of nailing. 

The homeowner could also brace gables and rafters. Tension straps could be directly fastened to roof members How Long Do Hurricanes Last in readily accessible areas. Adhesives could be used where there is insufficient access.

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