The roof is an important element in providing protection from the weather and contributing to the aesthetics of the building. The roof also has a significant role to play in the reduction of heat loss from a building. Roofs are classified as being either pitched or flat. Timber is the most common material used nowadays, usually in the form of prefabricated timber trusses. Although it is common practice to construct pitched roofs from prefabricated timber trusses, space has been reserved in this discussion for the traditional timber roof built on site, primarily as an aid to understanding the construction and terminology, but also as an aid to those involved in repair and refurbishment projects. The traditional site‐built roof is included in the chapter to explain the main principles of roof construction. Roof coverings range from natural slates, clay and concrete tiles, through to metal sheet materials, membranes and green roofs.
6.1 Functional requirements
The functional requirements of a roof are:
- Strength and stability
- Resistance to weather
- Durability and freedom from maintenance
- Fire safety
- Resistance to the passage of heat
- Resistance to the passage of sound
- Resistance to air leakage
Strength and stability
The strength and stability of a roof depends on the characteristics of the materials from which it is constructed and the way in which the materials are formed as a horizontal (flat) platform or as a triangular (pitched) framework.