![]() If you have a single sloped roof, then the 11’ span distance for 2×4 rafters O.C. Therefore, for gable roofed sheds, the rafter span table is indicating how far a rafter can span half of your shed’s width. If you have a gable roof on your shed, you’ll have two sets of rafters, with a ridge beam in the center uniting the rafters on each side. For instance, 2×4 SPF shed rafters can span up to 11’ when placed at 12” O.C. Understanding this is key to knowing how far your rafters can span. Another way to look at it is from the beginning of the birdsmouth cut to the opposite, interior facing edge. The span length is the measure taken from the inside of the shed framing to the interior apex of the rafter. If you forget to look at the store, don’t worry – the wood itself is usually marked SPF or SYP. There is a slight drop off in strength when using SPF for shed roof rafters, but in most areas, you only have one option when you go to your local home reno store, so at least know what you are buying. SPF is light and easier to use when framing. SYP is one of the densest softwoods, so it is strong but more difficult to cut and nail into. ![]() Many rafter span charts delineate between rafters using SYP (southern yellow pine) versus SPF (spruce, fir, pine) lumber. We will be looking at roofs that have a pitch of 3:12 or greater. While there are benefits to both, only rafters vary in the size of lumber that is used.įor more information about roof framing and how understanding the differences between types of shed roof construction, visit my guide to shed roof framing. Rafters simply rely on a center ridge beam and the outside walls for support. Trusses only use 2×4 lumber and are constructed using a “web” of 2x4s for strength. Lastly, remember that we are not talking about trusses in this article – just rafters. The reason for this is that flat or shallow roofs withstand much more abuse and loads than steeper roofs, making wider shed roof rafters a necessity. Many shingle manufacturers recommend no less than 2:12 when installing. Many roof material manufacturers have minimum pitch ratings for their products. 2×4 rafters are not strong enough for low pitched roofs under any circumstance, so avoid if you are building a shed with a flat or very shallow roof. If you look at the chart linked above, you’ll notice that for roofs that are less than 3:12, the chart does not include 2x4s as an option. ![]() What does 3:12 mean? It means a roof that rises 3 inches for every 12 inches of horizontal run. When talking about framing a shed roof with rafters, you’ll first need to know how steep your roof is – in other words, what is the pitch or slope of your roof? Most rafter span charts are organized into 2 sections: roofs with a slope less than 3:12 and roofs greater than 3:12.
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