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A beam hanger, also called a joist hanger, is a mechanical device used to fasten joists and rafters known as carried members to beams and headers known as carrying members. Beams and joists may be constructed from dimension lumber, timber, structural composite lumber, wood I-beams, or metal in a variety of sizes, so these beam hangers vary in size and design. Beams and joists are attached to each other by fasteners driven, bolted, or screwed through holes in the beam hanger to both the carried and carrying member.
The design of steel beam hangers is determined by the function of the carried member, either joist or rafter. A joist is a carried member that is horizontal and is generally attached to a beam via a joist hanger at a 90° angle. Any structural attachment should utilize hangers and fasteners as identified in the engineer’s or architect’s material specification list for safety and adherence to building codes. Special I-beam hangers are available to accommodate the popular wood I-beams often found in residential construction.
A rafter has slope measured in rise over run, such as a one-in-four pitch. That is, for every four units of horizontal measurement, the rafter slopes up one unit. When building design calls for a hip roof or a roof with one or more ells, rafters also have a skew, which means they meet the carrying member beam at an angle other than 90°.
When a rafter has both slope and skew where it meets a beam, a compound miter cut is required for a typical attachment. Specialized beam hangers are available during installation to adjust on-site to most angles of skew and slope. Some vendors have produced a beam hanger that requires the builder to cut only for a slope angle and reduce production time by saving a miter cut for skew.
For multi-story commercial construction requiring hot-formed I-beams, attachments are typically made using techniques and designs involving welding and rivets; they are not generally used by residential and light commercial builders. Metal rafters and joists used in most residential and light commercial building are cold-formed and have joist hangers especially designed to accommodate their shapes and material. Self-tapping metal screws are used as fasteners in most of these applications, although attention must be paid to the specification list to ensure safety and code compliance.
Two common designs of steel beam hanger are generally available through building supply outlets and hardware stores. They are the face-mount beam hanger and the top-flange beam hanger. The top-design has tabs set at 90° to the face of the beam hanger and rests on the top surface of the carrying member.
Advantages of the top flange on a joist hanger are primarily speed of installation, while disadvantages include bumps created in a sub-floor and the requirement of a precise fit of the dimension lumber used for the rafter or joist. A face-mount wood beam hanger takes a bit more time to install accurately, but it is much more versatile in use. In either case, it is important that the seat, the bottom of the hanger on which the carried member rests, is the same dimension as the joist or rafter and that the side flanges are not longer than the height of the joist or rafter.
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