When roofing a home, there are two roof framing systems used—rafters and trusses. Rafters and trusses provide the roof support for your home. It’s crucial that whichever your home uses, it is in proper working condition to provide the necessary support for your homes structure.
Roofs that are framed with rafters use individual rafters, which is just sawn lumber members, that are spaced at about 24 inches on center and go from the exterior walls to the ridge or into the sides of the main hip rafters. Commonly referred to stick-framing, this roofing style consists of two-by-sixes. But, because of the use of this small size, they don’t span very far and need to be braced near mid-span.
In most roofing structures, the roof-bracing system carries the majority of the weight of the roof. Because of this, it’s crucial that the roof braces rest on the load-bearing walls and not the most convenient interior room partition wall. While this seems standard, many framers often support the roof bracing system on the closest wall, which leads to floor sag and other complicated issues in the structure.
Along the peak of the roof is a ridge board that is used as a bearing-plate for the opposing rafters. And while the ridge board does not provide any structural support, it is required that it be tall enough to be placed in full contact with the cut face of the mating rafter and that opposing rafters align directly with one another.
These requirements are vital to the structural integrity of the home. When the ridge board is not structurally sound, the roof rafters should be lapped alongside and connected to the underlying ceiling joists at the exterior wall plate. And, the ceiling joists that extend across the home must be properly lapped and connected to create a tension-tie across the home. If these standard practices are lacking, the roof ridge will sag and the exterior walls will begin to lean outward.
Roof systems framed with trusses use pre-engineered, light-gage-plate-connected sawn lumber members fabricated according to a proprietary engineering design. The benefits of trusses include its ability to withstand structural load requirements and difficult roof framing configurations.
Trusses are able to transfer all of their load to the outer bearing points, thus, they do not need any support from interior room partition walls. However, truss-framed roofs can still create floor sag and other issues. When trusses are excessively long, they become flimsy and fragile. Unless handled with extreme care, during the erection process, the metal-plate connection can detach from the wood members and the truss can no longer be used.