The IRC provides details about 2圆 rafter spans under various spacings and loading conditions. Rafters are capable of spanning longer than joists because they have to carry less loads. The dead load on rafters incorporates loading caused by wind, snow type of ceiling finishing, and weight of the ceiling material (metal, tile, etc.). Similar to joists, rafter spans are also influenced by wood species, wood grades, spacing, and loads acting on them. Rafters are used to support sloping roofs of houses. 2圆 Ceiling Joists.ĭepending upon the ceiling finishing, the dead load is about 5psf for drywall and 10psf for a plastered wall.įollowing is a table extracted from the IRC 2021 that showcases the different span lengths of 2圆 ceiling joists under a 5psf dead load and a 10psf live load. In this case, the joist span will have to be selected using floor joist tables. The minimum possible span for 24” spacing provided in the IRC is 13’-1” for grade #2 Southern pine wood.Īs evident from the code, all the spans for ceiling joists are relatively longer as compared to floor joists.Ĭeiling joists are used to support the weights of attics and ceilings and roofs, but if the attic accommodates a sleeping space, then ceiling joists act as floor joists. The SS grade of the Douglas fir-larch is the maximum spanning member available in the IRC for a 2圆 ceiling joist, having a span length of 20’-8”. It is advised to check into local codes as well before proceeding with construction.įollowing is a table extracted from IRC 2021 that showcases the different span lengths of a 2圆 floor joist under a 10psf dead load and a 30psf live load.įor general floor joist span guidelines, read this: Floor Joist Sizing, Span, Spacing: IRC Requirements How Far Can 2圆 Ceiling Joists Span?Ĭeiling joists have to bear relatively lesser dead and live loads as compared to floor joists, and as such, have the tendency to span greater lengths. There are more spacing and loading conditions available in the code that give off different values for the span length of a 2圆 floor joist.Ī 2圆 floor joist is often used in small cabins, sheds, or small two-story houses. Similarly, a Southern Pine joist will now span 10’-9”. Similarly, for all of the above conditions, a Southern Pine wood 2圆 joist spans 11’-10”, whereas a Hem-fir spans 11’-7”.Īs is evident, the span length increases as the spacing decreases.Ĭhanging the spacing to 16” and keeping the rest of the conditions the same, a notable decrease in the span lengths is observed.Ī Douglas fir-larch will now span 10’-11”, and a Hem-fir will span 10’-6”. It is all based on the wood specie, grade, spacing, and loading.Ī structural select (SS) grade 2圆 joist made from Douglas fir-larch has the greatest span length of 12’-6” for a 10psf dead load and 12” spacing, as indicated in the IRC 2021.Ī grade#1 Douglas fir larch floor joist under 10psf dead load and 30psf residential live (sleeping areas) and 12” spacing spans a total length of 12’. How Far can 2圆 Floor Joists Span?Īccording to the IRC, a 2圆 floor joist can span anywhere between 6’-10” and 12’-6”. A same-grade and specie joist tends to have a smaller span as compared to a rafter under the same load. Loads also play a key factor in limiting span lengths. You will find different spans for the same-sized member in the case of a joist, a beam, or a diagonal rafter, Spans vary depending on differing conditions. In addition to effective spans, there are also clear spans ranging from one face of the support to the other. A length measured as such is known as the effective span. It is usually measured center to center in between supports. Span is the measurement of the length in between supports. This article is aimed at clarifying what a span is, how long a 2圆 can span as different structural members, without having any support, and what factors influence these spans. Thus, there is not a single maximum value for the spans a 2圆 can achieve when used as floor joists, ceiling joists, rafters, or in deck boards, etc. The span length for a 2圆 or any type of wooden structural member relies on wood species, wood grade, the spacing between the members, total loads, and their location. The selection of a span size is quite challenging and requires notable considerations. These values are only possible if the members are made with the SS grade (structural select) Duglous fir-larch wood type. According to the International Residential Code 2021 (IRC), the maximum length a 2圆 can span as a floor joist is 12’-6”, as a ceiling joist is 20’-8”, as a rafter is 18’-0”, as a deck board is 24', and as a deck joist is 9’-11”.
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