7) On a small hip roof (a maximum of 18 feet wide and 30 feet long) every other rafter has a collar beam with a collar beam at the hip tying the center hip rafter collar beam into the common rafter collar beams (Fig. One method of achieving this is to cast the ring beam in two parts. This roof usually has rafters spaced at a maximum of three feet and is sheathed in 1×6 tongue and groove boards on top of which is a layer of #15 roofing felt. Recommended bases: Manufacturers names are only used for ease in identifying types of products. Consideration should be given to increasing wind design loads and “x” bracing requirements when designing these structure for use in the Virgin Islands. The anchor bolt shears off at the concrete and the column is carried away. (Fig. Any similar base produced by other manufacturers is also suitable. It is therefore important to be aware of the tensile forces, which stress walls during a storm. Wind-resistant design is particularly important in hurricane- and tornado-prone regions. They are intended to be used as a guide to provide the general public with more information on building design and hurricanes and to foster the construction of structures which are better capable of withstanding hurricane force winds. I would strongly urge building suppliers to discontinue stocking this type of post base altogether. 1), When compared with the typical “stateside, ranch type” of gable roof with its overhanging eaves and blunt ends (gables) you can see that this type of roof provides more opportunity for the wind to grab the roof around the edges and rip it, Porches and galleries were added to West Indian hip roof structures as separate attached shed roofs, not connected to the main roof, to give sun and rain protection to the walls and openings. Sorry, there was a problem submitting your form. Their negative quality is that they tend to be more susceptible to damage from high winds than conventional structures. Two such examples are Simpson CB Series Column Base and Simpson EPB Series Elevated Post Bases. This produces a very strong wooden box, which if properly attached to its foundation and its roof, can survive such a storm. Design Wind Speed and Pressures The basic wind speed is reduced or enchanced for design of buildings and structures due to following factors: (i) The risk level of the structure measured in terms of adopted return period and life of structures. The exterior of the frame is then sheathed in wood siding or wooden T&G boards with shingles applied over it. The four sloping sides of the roof provided minimal resistance to the wind and allowed the wind to blow over and around the roof regardless of wind … These post bases have failed in hurricane force winds in two ways: 1. Observation of damage patterns also indicates that there were possibly tornadoes localized within the storm. TRADITIONAL BUILDING MATERIALS The reasons for this will be discussed here in detail. Many shed roofs of traditional design have survived the storm. A roof’s purpose, in a continuous load path, is to transfers the loads imposed by heavy winds to the supporting walls underneath. These buildings are relatively less expensive to build, when compared with conventional construction and provide very large, unencumbered spaces within. The type of column base used plays a major part in the anchorage system of shed roofs. A strong continuous load path is critical to holding the roof, walls, floors, and foundation together during a strong wind event of winds of over 200 mph. Another system, commonly used in the Virgin islands is to have the wooden roof joists cast into the concrete ring beam so that the top of the joist and the top of the ring beam are level with each other. In situations where galvanized roofing has blown off and left the wooden framing intact, it appears that it is the perlins to which the galvanized is nailed that is breaking away from the wooden rafters. This frame can then be covered with its interior and exterior skin, be it wood siding or metal lathe and plaster, all of which have the capabilities of withstanding hurricane force winds if the interior framing is properly secured to its adjacent members. Properly installed let-in bracing is a major key to the survival of wooden structures. This design greatly lessens the potential for the wind to get up under the eaves and lift the roof off. The whole island suffered devastation. These design guidelines were produced in the aftermath of Hurricane Hugo, which devastated the U.S. Virgin Islands in September of 1989. (Fig. Mandated in higher wind regions are ring-shank nails. This re-bar is also attached to another re-bar projecting from the lower portion of the ring beam. If the porches and galleries were to blow away in a storm, they could be attached so as not to take the main roof with them. The rafters stop at the edge of the walls. The information in this booklet is provided for reference only. As we travel around the islands we see that it is these traditional buildings, that as a group, have survived the storm best. Wall systems constructed with Fox Blocks insulated concrete forms (ICFs ) ensure a wind-resistant structure with a strong continuous load path that holds the roof, walls, floors, and foundation together during an intense wind event. One system of anchorage of wooden roof members to masonry walls is shown in Fig. A continuous load path ensures that when a load, including uplift and lateral (horizontal) loads, attacks a structure, the load will move from the roof, wall, and other parts, toward the foundation and into the ground. Every major component of the structural system must be securely tied to each other and to the foundation so that there is a direct structural link between the roof and the ground. Recommended in the corner zones eaves and the roof, where winds can cause large uplifts, are wood nails. The lower part contains the typical reinforcing required for the ring beam. To download this file, please fill out this form. All Rights Reserved. 2. Structural failure will occur first in the weakest link in this chain. Critical to wind-resistant building design is a continuous load path with strong roofs, walls, floors, and foundations, and impact resistance. Unfortunately, many times in the past, this type of connector is the only type available on the island. In larger hip roofs, especially in older historical structures the system of bracing and collar beam usage can become quite extensive. Importantly, a report by the Portland Cement Association (PCA) concluded that ICF walls have greater structural capacity and stiffness to withstand the in-plane shear forces of high wind than wood- and steel-framed walls. 6). In conjunction with this failure, as the shed roof blows away, its connection to the flashing between the galvanized shed and main roof becomes a significant detail. Columns should be bolted through these bases (Fig. The following untested detail (Fig. The joists are then set on top of this and a hole is drilled trough the joist and a #4 re-bar extended through the joist. The steep pitch provided a large volume of air space high in the building, which allowed the hot air to rise, and contributed to the cooling of the structure.