Standard house roofs today are built mostly with a symmetrical (equal) pitch. There are many individual shapes and styles, but they are all built to keep out the elements, wind, rain, snow and even excessive sunshine.
Roof construction in the UK up until the 1960’s was the domain of specialised carpentry, cutting all the required timber lengths by hand on site to each and every different buildings specification.
Traditional, or cut roofs are still utilised but normally for one-off designs or for the roof space to be used as extra living space.
Today’s most commonly used roofing structure is the prefabricated roof truss. These are triangular timber structures, designed and manufactured in a factory. They are then transported to the building site and lifted into place by crane.
The design is very important, to ensure that once the house walls have been topped, or framed the roof carries its weight to the load bearing outside walls.
Around three quarters of new homes constructed today use pre-fabricated roof trusses instead of traditional rafter roof support.
In the traditional build, the ultimate strength of the roof could be variable depending perhaps, on the ideas of the builder, the timber available and quality of the carpenters.
A truss roof system is designed and made in a factory to specific requirements and also come up to building regulations and codes, which allows for more standardisation of size and pitch of the roof.
Because they are manufactured under controlled conditions the risks associated with building sites, of damage and exposure to the weather are avoided.
The most commonly used truss is the Fink or W type, which is a duo pitch truss, which is two equal sloping surfaces meeting in the middle at the apex of the triangle.
They are placed at regular equal spaces to suit the type of load they are to bear.
These are placed on top of the load-bearing external walls of the house.
The heavier the load the closer the trusses are placed. The usual spacing for the average house build is two feet.
In most house builds the end walls are finished in a triangle. These are known as the gable ends and the end truss or couple of trusses are fixed to the inside face of them.
This helps stabilise and bind the timbers, as does the battening for the tiles.
The bottom length of the trusses’ triangle, the horizontal, is also a ceiling joist, the ceiling being attached to the underside.