Rafter and roof joist spacing is only one part of a complex roof design that works together to form a structure that meets building codes and can hold up the weight of the roof and roof load.. Chapter 8 roof-ceiling construction section r801 general r801.1 application. rafters, trusses and ceiling joists shall be identified by a grade tional building code. 2. identification of the treating manufacturer. 3. the name of the fire-retardant treatment. 4. the species of wood treated.. There are 3 accepted standard spacing for roof rafters based on local code. you don't mention what state/county you are in so this is a general statement. framing would be either 12", 16" or 24" on center ( center of the beam to center of the beam)..
Commonly used residential building codes. international residential code (2009) form revised 5/10 . roof framing . 30. roof design. rafter shall be measured along the horizontal projection of the rafter. conjunction with these standards the design shall comply with the international building code. 1. american forest and paper. These rafter spans are for #2 lumber, a ground snow load of 30 psf, the ceiling not attached to rafters, and a dead load of 10 psf. all other data can be found in the 2012 international residential code rafter spans. be sure to use rafter clips on every rafter not nailed into a ceiling joist.. As an extreme example, with a 70-psf snow load, an 18-foot rafter span, 24-inch on-center rafter spacing, and rafter ties raised to their maximum 1/3 height, a 1.5 multiplier is applied, which results in a requirement of 59 nails for each rafter/rafter tie connection..
