![]() ![]() DIFF IN LENGTH OF JACKS 16 INCH CENTERS.HIP OR VALLEY RAFTER LENGTH PER FOOT OF RUN.COMMON RAFTER LENGTH PER FOOT OF RUN - this is the top line in the rafter length tables.Holding the framing square with the front of the blade facing you and the tongue pointing down and on your right, you'll see six lines of rafter tables: Here is the Identification of each line of numbers on the blade This key is at the left end of the front of the framing square Tables give the length of the rafter per foot of horizontal run.Ībove we see the key to the lines in the rafter length table. You need first to understand the type of rafter you are cutting.įor a common rafter, or for each of the other rafter types, these To use the rafter length tables on the framing square blade front Normally roof slopes are expressed as inches of rise per foot of Our sketch above illustrates the concepts of run (horizontalĭistance) and rise (vertical distance) along the length of a rafter. The full scale number will be the length of the rafter in inches for The rafter tables allow you to calculate the length of a rafter byĬhoosing a "full scale" number that matches the unit rise (slope or Here we describe how to use the rafter tables found on the front How to Use the Framing Square Rafter Length Tables - the Rafter Tables We also provide a comprehensive ARTICLE INDEX for this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need. This article series gives clear examples just about every possible way to figure out any or all roof dimensions and measurements expressing the roof area, width, length, slope, rise, run, and unit rise in inches per foot. Roof measurement methods: these articles explain various methods for measuring all roof data: roof slope or pitch, rise, run, area, and other features. How to use the rafter tables on a framing square to measure & lay out rafters or to figure roof pitch, slope, length, and all other roof and angle measaurements.Īlso use these tables for stair rise and run and riser heights and stair stringer layout. We have no relationship with advertisers, products, or services discussed at this website. With the purlin/bracing installed, the long rafter span would be broken into two shorter spans, thus allowing the rafter to carry additional load.īefore you decide on lumber sizing and span, consult your local building code officials to determine design loads for your area.InspectAPedia tolerates no conflicts of interest. You can break up a long span of rafters by installing a purlin and bracing on the underside. When calculating the span of joists or rafters, use the horizontal distance between vertical supports. The number 1 grade material is more expensive than the #2 grade, but if you can use fewer or smaller number 1 grade joists or rafters in your design, you may actually save money.ĭepending on the availability and cost of various size framing materials, it may be more economical to use larger joists or rafters in your design because you can typically use fewer of them. For example, you can span a #1 grade (no knots) southern yellow pine joist a greater distance than a #2 grade of the same species (with knots). The lengths and sizes of joists vary depending on the species and quality of the lumber used. To calculate maximum spans of additional species of lumber, use the Span Calculator or the Span Tables for Joists and Rafters on the American Wood Council website.Ĭonsiderations when using the Rafter and Joist Span Tables ![]() Contact your local building code officials to determine the building code for your area. Weigh all of the elements when designing wood structures. Some areas have wind and seismic conditions. For example, some localities get large amounts of snow, whereas others get none. Before determining the maximum spans for joists and rafters, you must know the load requirements for your region.
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