![]() ![]() However, most roofers use 2×6 and 2×8 rafters. Though important, we’ll leave out the length for now.Ĭommon rafter sizes are 2×4, 2×6, 2×8, 2×10, and 2×12. Size here primarily refers to the dimensions that impact the thickness, thus the width and depth. Rafter Sizeīesides material and grade, consider each rafter’s size. Similarly, you need more rafters when using lower-grade lumber. For instance, weaker softwood lumber, such as spruce, necessitates more rafters per square than a hardwood like oak. The type and grade of the timber matter a lot. Meanwhile, steel offers better strength properties for industrial applications. Wood is the material of choice for residential roof construction. Rafters are typically made from timber or steel. We’ll only consider the six most important ones. Rafter spacing depends on multiple factors. This means measuring from the first rafter’s center to the next rafter’s center. ![]() Rafter spacing is measured “Off Center” (OC). Alternatively, it’s a near-horizontal member that doubles up as a roof joist on flat roofs. A rafter is a diagonal framing member on pitched roofs running from the apex of the roof to the roof plate or the eaves. Rafter spacing refers to the horizontal distance between two parallel rafters on a roof. But 24-inch on-center spacing requires 50% fewer rafters, thus significant cost savings. Also, the rafters must be deeper (thicker), of a higher grade/quality, and from a stronger wood species. However, 24-inch on-center spacing exerts about 50% more weight on each rafter than 16-inch on-center spacing. Which is better? This guide explains everything you need to know to make an informed decision.īoth options are practical. But the big dilemma is choosing one between the two. But, more importantly, they’re the sole framing members responsible for distributing roof weight to the walls.įortunately, many roofers and homeowners already understand that 16 and 24-inch on-center are the standard rafter spacing measurements. Please contact the specific manufacturer to verify product availability.Roof rafters, the roof framing members running from the wall plate to the roof ridge, must be properly spaced.įor one, they directly impact joist and ceiling spacing and the integrity of the roof deck. All SFIA manufacturers may not produce all products listed in this publication. For the latest information regarding a particular manufacturer’s products, contact that manufacturer. The SFIA and its member companies reserve the right to make modifications and/or change materials of any of their products without prior notice or obligation. This publication contains the latest information available at the time of printing. These products should not be used in design or construction without an independent evaluation by a qualified engineer or architect to verify the suitability of a particular product for use in a specific application. All data, specifications and details contained in this publication are intended as a general guide for using SFIA member companies’ products. SFIA makes no representation, warranty, or guarantee in connection with this technical data and expressly disclaims any liability or responsibility for failure resulting from the use or misapplication of computations, detail drawings and specifications contained herein. * A concerted effort has been made to ensure the accuracy of the technical data represented in the Steel Framing Industry Association (SFIA) Technical Guide for Cold‐Formed Steel Framing Products. eBook: Specifying Cold-Formed Steel Framing: A Guide for Architects and Engineers.4 K-12 School Design Trends that Make Use of Steel Framing. ![]() Checklist for Architects and Engineers Writing CFS Specifications.The Steel Framing Industry Association (SFIA) provides its members with exclusive access to technical cold-formed steel (CFS) framing services, including the SFIA Steel Framing Learning Portal. SFIA member services include access to market data, market analysis, technical design guides, architectural services, environmental product declarations, CFS certification and more.Įditor’s note: This post was originally published in February 2022 and has been updated for accuracy and comprehensiveness.
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