Structural Insulated Panels

Structural insulated panels (SIPs) are prefabricated lightweight building components, used for load-bearing internal and external walls and roofs. Unlike cladding sandwich panels, structural insulated panels can support considerable vertical and horizontal loads without internal studding. They are manufactured from two high-density face layers separated by a lightweight insulating core. The three layers are strongly bonded together to ensure that the composite acts as a single structural unit. The outer layers of oriented strand board (OSB), cement-bonded particleboard or gypsum-based products are typically 8 mm to 15 mm thick. The core is composed of a rigid cellular foam, such as polyurethane (PU), polyisocyanurate (PUR), phenolic foam (PF), expanded (EPS) or extruded (XPS) polystyrene, giving an overall unit thickness

Portal frame A-frame
Fig. 4.22 Glued laminated-timber beams. Photograph: Arthur Lyons

between 70 mm and 250 mm. The structural performance is predominantly influenced by the thickness and physical properties of the outer layers, and the thermal performance is largely determined by the width and insulating characteristics of the core material.

Structural insulated panels (typically 1.2 m wide by 2.4 m high) offer a thermally efficient and air-tight form of construction, which is rapidly erected on site.

Jointing between panels is usually some form of tongue and groove system. Sound reduction for separating walls is typically 58 dB depending upon construction details. External cladding may be brickwork, wooden panelling or rendering with plasterboard as the standard internal finish. Table 4.12 gives typical thermal performance data for structural insulated panels.

Fig. 4.23 Thames Barrage, London. Photograph: Arthur Lyons
Table 4.12 Thermal performance data for Structural Insulated Panels (SIPs)

Core material

(W/m2K)

Polyurethane

cement bonded

foam

particleboard

86

0.28

Polyurethane

oriented strand

foam

board

100

0.23

Polyisocyanurate

oriented strand

foam

board

140

0.22

The thermal performance data (U-values) are typical for the listed SIPs when constructed with a brick outer leaf and 50 mm clear vented cavity.

The thermal performance data (U-values) are typical for the listed SIPs when constructed with a brick outer leaf and 50 mm clear vented cavity.

reconstituted wood. In the other processes, 3-mm-thick timber strands or sheets of veneer are coated with waterproof adhesive and bundled together with the grain parallel. The strands or veneers are pressed together and microwave cured to produce structural timber billets or sheets up to 26 m long. The versatile material is suitable for use in columns, beams, purlins and trusses, and can be machined as solid timber (Fig. 4.25). I-section joists, with LVL flanges and web, are suitable for flat and pitched roofs and floor construction. Untreated LVL has a Class 3 surface spread of flame classification (BS 476-7: 1997). Three grades of laminated veneer lumber are classified according to their serviceability in dry and exposed conditions.

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