Rafter Vs Joist On Flat Roof

This is our ultimate roof rafter guide for people designing and building an off grid cabin or tiny home.

Rafter vs joist on flat roof. The size of rafters for a flat roof depends on the horizontal span of the building the type and grade of timber used and the load on the roof. A joist is a horizontal structural member used in framing to span an open space often between beams that subsequently transfer loads to vertical members. They are nailed securely to exterior wall plates and to each other. The major functional difference between the two is that trusses are built mostly with 2x4s in place of the wider dimensional boards.

Discover the pros and cons to multiple roof designs. Rafters are the building components that run diagonally from the wall plate to the apex of a roof structure. Similarly ceiling joists are the planks of wood that create the flat surface of your attic floor or top story ceiling. Learn the 1 rafter design that will guarantee your roof that is safe and strong for years to come.

Ceiling joists can be on both low sloped roofs and high sloped roofs and help to prevent racking and spreading of your rafters or walls which could lead to sagging. Rafters form the foundation for attachment of the roof boards onto which the final roof covering is fixed. In traditional timber they are nominally 2 inches thick and typically 8 to 10 inches wide. For heavy roofs or in areas with substantial snowfall or winds call your local building department for code requirements.

The rafters in a flat roof serve as ceiling joists for the space below. Trusses and rafters have many common parts including the sloping rafter boards and a bottom joists that form the ceiling of the space below.