Building with Flat Roof Trusses
There are dozens of different kinds of trusses used in the construction of buildings. Flat roofs generally have a pitch of less than ten degrees and this type of roof requires special flat trusses. This still provides the necessary weight distribution while taking up minimal space. These trusses are not actually flat, but slightly sloped which prevents water from pooling on the roof and collapsing or damaging the structure.
Roof Trusses are generally made from kiln-dried timber or steel comprising of joined pieces secured with nail plates to form a strong roof support. Flat Roof trusses are one of the more common types of roof trusses. However, they are more inefficient than other types of trusses and are generally used when specifically requested by the homebuilder or to compliment the particular design of the building.
When to Use Flat Roof Trusses
Flat Roof trusses have an advantage when used on column and lateral-bracing connections. This is because their top and bottom chords can be attached directly to the columns. The stress on the web of flat roof trusses are greater than other types of trusses though. Therefore, in order to have a safe web connection structure that can withstand the weight of the roof materials, it will probably be more complicated and expensive construction process.
The Maximum Roof Load and Truss Span
Flat roof trusses are not often used for roofs that span more than 80 ft. They have an average loading and spacing of up to 20 ft, and they are limited by the timber length that is available. Flat roofs will also need to carry more weight than a more sloping style of roof. A dead load is the weight of the roof itself, while the live load weight is the additional weight that may be placed upon the roof later – keep this in mind when planning the design. This can include the weight of construction workers, snow or water.
Types of Flat Roof Trusses
There are a few different types of flat trusses that can be used in flat roof construction. The length of the roof, the weight it will be required to hold and the pitch of the roof are all factors in deciding which type of truss should be used. If the trusses are made of wood, a Howe Truss can be used. For spans longer than 80 feet, segmental arch trusses provide more support. Lattice trusses are ideal in locations where large timber or iron rods are unavailable or cost prohibitive.
Building a flat roof has special considerations. They will need to support a heavier load than a pitched roof which would allow snow and water to slide off more easily. Understanding the benefits and limitations of flat roof trusses will help determine if they are the right type of roof truss to use for your home or building.