What is a beam layer?

A beam layer is the complete set of parallel timber beams that forms the load-bearing structure of a floor, ceiling, or roof. The beam layer carries vertical loads — including the self-weight of the floor, furniture, and occupants — and transfers them to the supporting walls or columns below.

Construction and classification

A beam layer consists of a series of beams placed at regular centres, typically between 300 and 600 millimetres apart. The beam dimensions (width and depth) are determined by the span, the imposed load, and the timber species used. Common species for beam layers include spruce, pine, and in historic structures, oak.

There are two principal types of beam layer:

• Single beam layer: a single tier of beams spanning directly from wall to wall. This is the most common and simplest arrangement.
• Composite beam layer: a system of primary and secondary beams, where the primary beams bridge larger spans and the secondary beams rest across them at right angles.

Application

Beam layers are found in both historic and modern buildings. In residential construction they serve as:

• Intermediate floors between storeys
• Attic floors beneath the roof structure
• Ground floors above a crawl space

In timber-frame construction and CLT (Cross Laminated Timber) buildings, the beam layer is a fundamental part of the structural system. In existing buildings, the condition of the beam layer is a key factor in determining the load-bearing capacity and remaining service life of the floor.

Structural design

The structural design of a beam layer is carried out in accordance with Eurocode 5 (EN 1995) and considers deflection, shear, and vibration criteria. A structural engineer uses these standards to determine the appropriate beam cross-sections and spacings for the specific loading conditions.

Related terms

• Beam floor construction
• Single beam layer
• Composite beam layer
• Beam end
• Floor joist
• Wall plate
• Timber-frame construction

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