2001 ASD Supplements - unprotected PDF - American Wood Council

L-44 SPAN TABLES7.1 Universal Span TablesThe tables in this Section provide joist and rafter spansfor design criteria listed at the top of each table. Spantables are provided for the following commonly used loadand deflection criteria:Applications Live Dead Deflection TableLoad Load Limit No.(psf) (psf)Floor joists 40 10 span/360 7.130 10 span/360 7.2Ceiling joists 10 5 span/240 7.320 10 span/240 7.4Roof rafters 20 15 span/240 7.530 15 span/240 7.640 15 span/240 7.720 10 span/240 7.820 10 span/180 7.9The applications and associated load and deflectioncriteria listed above are commonly encountered in designsof residential wood structures. The use of the tables is notlimited to the applications listed.These span tables for joists and rafters are calculatedon the basis of a series of modulus of elasticity (E) andallowable bending design values (F b ′). The range of valuesin the tables provides allowable spans for all speciesand grades of nominal 2-in. framing lumber customarilyused in construction. These span tables assume installationof at least three joists or rafters that are spaced notmore than 24 in. o.c. The calculated spans assume fullylaterally supported members, properly sheathed and nailedon the top edge of the joist or rafter.Lumber Design ValuesUse of these span tables requires reference to the applicabletabulated design values for the various speciesand grades of lumber. These tabulated design values arefound in Tables 4A, 4B, 4C, and 4F of the NDS Supplement.Span MeasurementThe tabulated spans are shown in feet and inches. Thespans are the distance from face to face of supports whichdoes not include one-half the required bearing length ateach end. For sloping rafters, the span is measured alongthe horizontal projection.Use of Universal Span TablesSpans for floor and ceiling joists are calculated on thebasis of the modulus of elasticity (E) with the requiredallowable bending design value (F b ′) listed below eachspan. Spans for rafters are calculated on the basis of allowablebending design value (F b ′) with the requiredmodulus of elasticity (E) listed below each span. Valuesdetermined from the span tables should be compared tovalues from Tables 4A, 4B, 4C, and 4F of the NDS Supplementmodified appropriately by the adjustment factors.Species and grades with allowable bending design valuesand modulus of elasticity values greater than or equal tothose shown in the span tables are appropriate.AMERICAN WOOD COUNCIL