roof terminology
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| Q | hip |
| A | A hipped roof is a roof which slopes downwards from the ridge to the eaves at the corners of a building. The hips are formed with hip rafters. The (jack) rafters are cut into the hip rafters for support. close |
| Q | rafter |
| A | A rafter is a sloping timber between the ridge and the eaves of a roof. The rafters sometimes span all the way from the ridge to the eaves, but sometimes additional support is provided by purlins. In residential properties, rafters are normally cut from lengths of timber. If the rafter is part of a truss it is called a principal rafter. In commercial buildings, such as steel portal framed structures the same terminology is used, but with this type of structure the rafters support the purlins, unlike with a residential roof. close |
| Q | purlin |
| A | A purlin is a horizontal beam which in traditional timber roof construction provides support to the rafters. If the purlin is at the ridge then it is called a ridge purlin. In steel portal frame roof construction the supporting arrangement is the other way around with the purlins being supported by the rafters. close |
| Q | trussed rafters |
| A | Most modern roofs are built with trussed rafters. These are a series of braced timber frames, normally spaced at around 600mm centres. They are normally supported on the outside walls of the building with no internal support being required. There are several different types of truss, with 'fink' and 'attic' trusses being the most common ones. Trussed rafters are manufactured in the factory, with pressed metal plate connections and then delivered to site. The supplier designs the trusses as part of their Contract. Their main advantage is that they are relatively cheap and they can be erected by semi skilled labour. close |
| Q | king post truss |
| A | these are traditional timber roof trusses used in buildings in this country from around the 17th century. Their configuration is a principal rafter on each roof slope, a tie beam between the bottom of the rafters, a central vertical post (the king post) and inclined struts from near the base of the king post to midway along the rafters. close |