Roof Joists Vs Rafters

Rafters are the building components that run diagonally from the wall plate to the apex of a roof structure.

Roof joists vs rafters.

Continuous ceiling joists or collar ties span from rafter to rafter. 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. The simplest is a planar truss which is used as a roof support system. In traditional timber they are nominally 2 inches thick and typically 8 to 10 inches wide.

There is no need for bearing posts under the ridge board which is nonstructural. This structural support comes in the form of roofing joists ceiling joists rafters or trusses and can be made from a variety of materials including wood metal reinforced concrete etc. However in canada the most common material used in residential framing is wood so that is the material we will discuss here. Trusses are of many types.

The major functional difference between the two is that trusses are built mostly with 2x4s in place of the wider dimensional boards. Joists are used in floors and as column support. Throw in the element of a construction budget and this is where rubber meets the road. In a typical roof framed with dimension lumber the rafters rest on the exterior wall top plate at the lower end and bear against a ridge board at the top.

Lastly remember that we are not talking about trusses in this article just rafters. They are secured at the bottom by ceiling joists. Rafters form the foundation for attachment of the roof boards onto which the final roof covering is fixed. Cost comparison of roof rafters vs trusses.

While rafters are less and less frequently used today due to the higher cost of rafters vs trusses they do have certain advantages. A rafter is a traditional roof framing method in the form of elongated lumber that s normally inclined from a central ridge beam and joins with the outer walls. What is a rafter. Constructing a roof using rafters is also known as stick framing which simply means that each rafter is built on site with lumber every piece of lumber is carefully measured cut and tightened together labor.

Trusses only use 2 4 lumber and are constructed using a web of 2x4s for strength. Collar ties placed horizontally halfway down the rafters hold the rafters and roof planes together. The joist also called bandsill supports the load which the floor is built to bear it is like the skeleton a building.