However, the roofing engineers can adjust these measurements as they see fit.Ĭonsidering the factors that determine the size of the rafters, it is most common to use 16- or 24-inches sized rafters.Įach rafter size can work with these roof spans. The industry standard for roof rafter span is in four dimensions: 12, 16, 19.2, and 24 inches, respectively. These factors include the building span, the timber grade used to make the rafter, and the load the roof carries. Knowing the size of rafters suitable for your flat roof depends on certain factors. There are four main rafter sizes which are 2×4, 2×6, 2×10, and 2×12.
What Size Rafters Should I Use for My Flat Roof?