These include, but are not limited to, the design live load, the span restrictions and the snow load of your area. It is best to consult a qualified building professional before selecting a rafter size, as there are other factors to consider as well. However, if you plan to use a metal roof or a two-story application, a 2×8 rafter may be more appropriate. For example, on a 16 foot span, with a pitch of 6/12 and a one-story application of asphalt shingles, a 2×6 will be sufficient. Generally, for a 16 foot span, your rafters will need to be 2×6 or 2×8 lumber, depending on the pitch and other factors. The size of rafters you need for a 16 foot span will depend on several factors, including the roof pitch you plan to use, the type of roofing material and the type of roofing framing system you plan to use, just to name a few. What size rafters do I need for a 16 foot span? When designing a rafter system, other factors also need to be taken into consideration, such as the roof pitch and the roof span.Īdditionally, roof trusses or other supports may need to be used if the span of the rafter is greater than 24 feet. The rafter needs to have a peak height of about 5.5 ft for this span, with a minimum end bearing length of 3.5 inches. Generally speaking, if you are using #2 grade Southern Pine, the rafter can span up to 24 feet when designed for a 20 PSF live load (e. How far can a 2×8 rafter span without support?Ī 2×8 rafter span without support depends on several factors, such as the species of lumber being used and the load that is being put on the rafter. It is important that the angles of the rafters are precise so they will fit securely in place and support the roof. Finally, once you have calculated the size of the rafters and the spacing between them, you will need to measure, mark, and cut the rafters. The size of the rafter you select will depend on the weight of the roofing material, and this can vary based on the type of material being used, such as shingles or tile.Īdditionally, you will need to calculate the correct number of rafters needed, accounting for the spacing between them, which should be between 24-48 inches. If you are using rafters, you will need to note the slope of the roof and select a suitable rafter type and size. If you are using a truss system, you can simply count the number of trusses needed, based on the length and width of the roof. In order to calculate the rafters for a lean-to roof, you will need to consider the overall length and width of the roof, the pitch of the roof, and the type of material being used for the rafters. How do you calculate rafters for a lean to roof? Ultimately, the span for a lean to can vary significantly depending on the type and design. Additionally, a ridge beam can be used to increase the span of a lean to, allowing for a longer span and increased load bearing capacity. Similarly, trusses can be used to span larger areas such as a garage, though the maximum is usually 12 feet. Generally, the maximum span for a lean to is between 18-20 feet, though this can vary depending on the roofing materials used and the configuration of the roof.įor example, if using trusses, the span can be extended up to 24 feet in some cases. The span of a lean to is usually determined by the width of the rafters and the distance between them. The span for a lean to is typically determined by the design and size of the building itself. Therefore, it is advisable to consult the local building department for lumber specific details before commencing the construction of a lean to structure. For example, a 2×6 of Douglas-fir can span up to 8’ – 0” if it is used as a joist and the total load on it is less than 30 lbs/sqft. Also, if the load on the structure exceeds 25 lbs/sqft, then the structural engineer should determine the maximum allowable span of the material.Īdditionally, different species of lumber will have different maximum span capabilities. If the lumber used is of a lesser grade than #2, then the length of the span should be reduced accordingly. Generally, a 2×6 of #2 Grade southern yellow pine can span up to 6’ – 0” if it is used as a joist and the total load on it is less than 25 lbs/sqft. The maximum span of a 2×6 board for a lean to structure depends on the load the structure needs to support and the species of the lumber.
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