Chapter D8 – Installs Engineered Trusses

Topic 1 – Types a Parts of Trusses

Types of Roof Trusses

There are a variety of roof trusses which a carpenter may encounter. Their design, which is determined by an engineer, is dependent on many factors including span, roof structure, and type of ceiling.

There are five basic trusses which are outlined below:

King Post Truss – the simplest of all trusses, it consists of an upper and lower chord with a center vertical post. It is capable of only small spans and typically used on small buildings and garages.

Find Truss (W Truss) – one of the most common truss designs, it can span greater distances (up to 26’) than the king post.

Scissor Truss – used for houses when a sloped ceiling is desired. To accommodate for insulation and strength, the bottom chords typically have a slope ½ as steep as the upper chords.

Howe Truss – a similar design to the howe truss, it has center and intermediate posts and is capable of spanning up to 36’

Attic Truss – used when storage or living space is desired in the attic space.

Parts of a Truss

The following diagram shows parts of a typical truss:

Review Questions

1. Name the following trusses:

2. A member extending from one end of a truss to its peak, forming the top of the truss is the _____.
3. A member extending from one end of a truss to the opposite end, forming the bottom edge of the truss is the ______.
4. Vertical or diagonal members joining the top and bottom chords are _____.
5. The horizontal distance between supports is the _____.
6. The intersection point of the top and bottom chord is the _____.
7. The upward vertical displacement built into a truss to compensate for deflection is the _____.
8. The structural portion of a truss which extends beyond its support is the _____.
9. Components of a truss are either in _____ or _____.
10. Common trusses are usually spaced at _____ O.C.

Answer:

1. (From left to right, each row) – King post, Fink (W) Truss, Howe Truss, Queen post, scissor truss, attic truss.
2. Top chord
3. Bottom chord
4. Web members
5. Span
6. Heel
7. Camber
8. Cantilever
9. Compression or tension
10. 24”