Please distinguish it from the rafter length, measured diagonally along the rafter. The rafter span is the horizontal distance between the supporting wall and the center of the roof. Industrial roof construction projects mostly require 2×12 wooden rafters or steel rafters. However, for closely spaced rafters, you can use thinner lumber boards (2×4 or 2×6). Generally, you need thicker rafters (2×8, 2×10, or higher) for wider spacing. Meanwhile, the span size address all rafter length concerns. The “size” is mainly concerned with the width and depth. Rafter size is one of the most important factors when determining the right rafter spacing. However, the six most important factors are as follows Rafter Size Several factors influence rafter spacing. Rafters rely on their individual and collective “strength” to carry the loads and counter additional pressures, and spacing is critical for the “collective” strength. Meanwhile, a dead load is any weight-bearing feature permanently stationed on the roof, notably the shingles and decking. A live load refers to any temporary weight-adding factor, such as a contractor on the roof, wind, ice, or standing water. These loads are classified as live or dead in roofing circles. In addition, ice dams add significant weight in winter. Remember also that the roof is constantly up against winds and storms. Given rafters are the primary framing members responsible for carrying and distributing the roof load, any sign of laxity can bring the roof down. So, you can see the importance of rafter sizes and spacing. You need a strong framing structure to carry such weight without sagging or crumbling for decades. Meanwhile, a sheet of 7/16 OSB decking weighs 43.8 pounds, and you need about 50 per for a standard roof, adding 2,000+ lbs to the roof. This means the shingles alone weigh up to 3,600 lbs, equivalent to 24 average-sized adult humans. Yet, a standard roof is 1,500 square feet. Unfortunately, decks and roofs are heavy.įor instance, shingles weigh up to 240 lbs per square (100 square feet). Rafters support decks, which support the shingles or panels. Why is rafter spacing important? Because the wrong spacing leads to a weak roof, thus, a weak house. Measure from the center of the first to the center of the next. The same applies if measuring the distance between ceiling joists. “On-center” means measuring the distance from the first rafter’s center to the next rafter’s center. Rafter spacing is the shortest distance between two parallel rafters measured “on-center.” Alternatively, you can determine the rafter spacing by measuring the distance between two ceiling joists on-center. Many roofers join rafter feet with ceiling joists for a more rigid structure. But more importantly, they distribute the roof load down to the walls and the foundation for a structurally sound home. First, they provide a platform for decking installation. It’s eco-friendly, energy efficient, beautiful, and easy to install. They are laid side by side in a series to provide base support for roof decks.Īlthough steel is preferred in industrial construction, dimensional lumber is the best rafter material for residential homes. Rafters are roof framing members that run from the ridge or hip of the roof to the wall plate, eave, or downslope perimeter. Generally, the smaller the rafters, the closer the spacing. The exact figure depends on many factors, including the type of roof structure, roof design (style), etc. However, you can also space your rafters 12 inches or 19.2 inches on-center. The standard rafter spacing for metal roofs is 16 or 24 inches on-center. We also briefly explain rafter spacing requirements for various structures, including porches, pergolas, and sheds. Indeed, you can be penalized if a home inspection reveals improper rafter spacing.įor this reason, we’ve developed this guide to explain rafter spacing requirements for metal roofs on residential homes. However, the opposite is true, especially for the main home. Did you know that there are standard guidelines for roof rafter spacing? Unfortunately, many DIYers think you can space them as you wish.
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