Types of Roof Trusses

Types of Roof Trusses

A roof truss put simply, is a structure that includes one or more triangular units that include straight, slender members with their ends connected via nodes. The roof truss is what supports the weight of whatever material is used for the roof, be it slate or tile etc. Trusses have immense strength; the structure disperses the weight evenly, therefore, creating an incredibly sturdy construction. Trusses are also very versatile and can be used on a range of widths of buildings – just about any shape truss can be custom built. Additionally, any truss can be formed out of any material, be it steel, timber etc. Roof trusses are the ideal choice for all roofing projects including extensions, new builds, residential developments and commercial projects. Timber trusses come in two forms; prefabricated trusses and traditional trusses.

Prefabricated Trusses

Prefabricated trusses are used on nearly all modern mass-produced homes such as those constructed by housebuilding companies. The benefits of prefabricated trusses are that they are quick to construct, cheap to manufacture and easy to work with. The large span structures are delivered on a lorry, and then a crane is used to slot them into place on site. As they are prefabricated off-site, this minimises the installation time, working at height and the associated labour costs. Most of these trusses are fink; this is a basic webbed truss design that provides the most economical roof solution. The roof truss design is in the shape of a ‘W’ to provide masses of strength.

Traditional Roof Trusses

The other type of roof trusses is traditional roof trusses such as King Post, Queen Post and Fan, the likes of which you may see in old barns and houses. These methods are the more traditional approaches to building. These structures are durable and able to withstand a lot of pressure. The King Post truss consists of two principal rafters, a tie beam, a central vertical post (king post) and two angled struts and requires sophisticated joints between the tie beam and principal rafters. The Queen Post Truss consists of two principal rafters, a tie beam, two vertical posts (queen posts) and a straining beam. King post truss can span in the range of five to eight metres, whereas the Queen post truss can span from eight to twelve metres. The main characteristic of a fan truss is that the top chords are split into smaller lengths, therefore, allowing the build to obtain purlin support.

These traditional trusses are most common in 19th-century buildings and when used in modern buildings tend to be exposed features in bespoke houses and barn conversions. These trusses pretty much ceased to be used in the second half of the 20th century but have made a come back in recent years, particularly due to the popularity of oak framing. Skilled carpenters are required to make traditional trusses, cutting perfect joints and connections to ensure the stability of the structure.

Benefits of Roof Trusses

As most modern trusses are manufactured offsite, and ready to install when they arrive onsite, this reduces expense significantly. In addition to this, the structure of prefabricated trusses requires small pieces of wood, which is cheaper than purchasing larger parts. The speed of installation means that the interior of the build is not exposed for a long period of time; this minimises the risk of it being damaged by unfortunate weather conditions.

The design of traditional trusses can be customised to suit the look and layout you require and should be discussed with a Structural Engineer in order to confirm what is achievable.

Here at Martin Perry Associates, we are experienced surveyors and structural engineers who can assist with your truss design. If you have any questions about a particular project or require some advice, then please do not hesitate to contact us on 01579 345777.

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