A roof structure is the load-bearing assembly of a roof. In construction, every beam, panel and connection has its own technical term. This terminology makes it possible to read building drawings, specifications and details unambiguously.
Main components and their terms
A traditional pitched roof structure consists of fixed components, each with its own function and name:
- Truss — the triangular main load-bearing structure that transfers the roof load to the wall
- Ridge beam — the horizontal beam at the highest point of the roof
- Purlin — horizontal beam resting on the trusses, supporting the rafters
- Wall plate — horizontal beam on the wall on which the rafters rest
- Rafter — sloping beam running from the wall plate to the ridge
- Collar tie — horizontal beam between two rafters, prevents bowing
- Hip rafter — sloping beam at the outside corner where two roof planes meet
- Valley rafter — beam in the inside corner between two roof planes
- Roof sheathing — boards or panels on the rafters as substrate for the covering
- Battens and counter-battens — strips on which the roof tiles are hung
- Eaves — lower edge of the roof plane, often with gutter and fascia
Types of roof structures
The common wooden roof structures are:
- Rafter roof — without purlins; rafters rest directly on wall plate and ridge beam
- Purlin roof — with trusses, purlins and rafters; suitable for larger spans
- Scissor and A-trusses — factory-prefabricated trussed rafters
- Flat roof — usually steel or wooden joists with sheathing
Application
Knowing these terms is essential when reading building drawings, during alterations (such as adding a dormer that interrupts rafters), and when discussing the work with carpenter, roofer or structural engineer. On detail drawings, components are often shown with abbreviations, where the correct name prevents execution errors.
Related terms
- Roof structure
- Roof truss
- Rafter
- Purlin
- Wall plate
Want to learn more about construction terms? Visit our knowledge base at fredsdiyplans.com.