3/12/2024 0 Comments Ibc rafter span tables![]() ![]() It is wise to research the types of insulation you are considering and the R-factor you hope to obtain and then calculate how much depth you need in the rafter cavity. This is generally cheaper than building with a larger dimension of lumber. It is possible, however, to add pieces of wood onto the rafters to fur them out to allow for more insulation. So if your rafters are only 5 1/2" deep, that is all the space you have for insulation. Roof insulation for 1 1/2 story homes (a home where you have living space in the attic) is typically installed in the rafter spaces. In making your choice, consider how you will insulate your insulate your roof. Another option are 2 X 8 rafters spaced 24 inches o.c. The table states that 2 X 6 rafters spaced 16 inches on center (o.c) can span a maximum distance of 13 feet 5 inches. Looking through the center of the table, we can find a couple of options. Let's use this example and find a size of rafter that will work. So if your house is 26 feet wide and the roof ridge beam is centered on the house, you will need a rafter that can span 13 feet. The maximum spans in the table above are for the horizontal distance the rafter can span (NOT the diagonal distance or actual length of the rafter). This table is simply a sample and may not be valid for your region. Sample Maximum Spans (feet-inches) Douglas Fir or Larch, No.1 or No.2 with 31.3 psf of Snow Loading ![]() Let's look at the sample table below which shows maximum rafter spans for a snow load of 31.3 pounds per square foot (psf).įraming Table for Maximum Roof Rafter Spans If you live in a region that gets winter snowfall, contact your municipal building department to find out what maximum snow loads you need to design for.ĭepending on your region, you may need to design for a maximum snow load of anything between zero to 65 pounds per square foot (or roughly 0-3 kPa). All roof framing tables are organized by maximum snow load. In most regions, the first thing to consider before sizing the wood framing members for a roof is the maximum snow load that the roof will have to bear. Initially, we will discuss the framing of gable roofs so that we can learn the basics of how to size a roof rafter, beam or joist. Each rafter is in turn fastened to the top of the exterior structural walls.Īs we discussed in Exterior House Designs there are many different house roof types. Along the top center of the house there is a beam to which are attached the rafters. The image below shows a cross-section of our simple 12' X 13' house from the joist span tables section of this tutorial. Let's consider a basic gable wood roof framing design. To calculate the maximum spans of species not shown above, use the Span Calculator or the Span Tables for Joists and Rafters on the American Wood Council website.Continuing on from Part 3: Floor Beam Span Tables of Residential Structural Design, we will now look at roof rafter and beam design. To calculate maximum rafter spans using different design criteria (load, snow load, spacing, grade, etc.) for these common lumber species, see the International Residential Code (IRC). The span values (displayed above) are from the American Softwood Lumber standard sizes. Rafters with ceiling not attached to rafters, ground snow load = 50 Psf, dead load = 20 Psf, deflection limit L/180 ![]() The following span table uses a moderate snow load of 50 Psf, but yours could be more or less. Consult your local building code authority to determine the snow load in your area. Note: Snow load factors can be specific to the regional location of a structure. Rafter Span Tables Rafters with ceiling not attached to rafters, live load = 20 Psf, dead load = 20 Psf, deflection limit L/180 The braces need to be supported by a bearing wall, shown in the diagram above.Įxample: In the rafter span table below, the highlighted cell (13-0) indicates that a 2" x 8" Douglas Fir rafter, with a grade of #2, spaced 24" apart, can have a maximum span of 13 feet - 0 inches (13-0) if designed for a live load of 20 Psf, and dead load of 20 Psf. Note also that you can break up the span of a rafter by adding a purlin and bracing to the underside. ![]() When calculating the maximum span of a rafter, use the horizontal distance between two vertical supports. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |