What is sheet material?

Sheet material is the collective term for building materials supplied as boards, with which you close off a large area in a single operation. It covers plywood, OSB, chipboard, MDF, plasterboard, cement-bonded boards and fibre cement boards. They are used to sheathe walls, ceilings, roofs and floors, as a substrate for finishes, and as structural racking panels.

The main types

• Plywood — cross-bonded veneer layers; strong, stiff and dimensionally stable in both directions. Available in interior and exterior grades (different adhesives) and in species from softwood to birch and okoumé.
• OSB — large, oriented wood strands bonded in layers. Cheaper than plywood and well suited to structural wall and roof sheathing.
• Chipboard — fine particles; flat and inexpensive, but more moisture sensitive. Moisture-resistant grades exist.
• MDF — pressed wood fibres, even and smooth; ideal for painting and routing, but not moisture resistant in standard form.
• Plasterboard — a gypsum core with paper facings; the standard internal lining for walls and ceilings, with variants for moisture, fire and sound.
• Cement-bonded and fibre cement board — for wet and fire-exposed situations, outdoors and behind tiling.

Sizes and thicknesses

Common board sizes are 2440 × 1220 mm and 2500 × 1220 mm, alongside longer boards (3050 mm, for example) for ceilings and tall walls. Plasterboard is usually 600 or 1200 mm wide, matched to stud spacings of 300, 400 or 600 mm centres. Always design the framing around the board size: joints then land on a stud and waste stays low.

Choosing: what to check

1. Moisture. The key question. Standard chipboard and MDF in a bathroom or external wall swell irreversibly. Choose moisture-resistant grades or move to fibre cement.
2. Structural or not. Only boards of the right grade may be used for racking or as a roof diaphragm. Ask for board with the matching declaration of performance; not every “OSB board” qualifies.
3. Finish. MDF needs primer on cut edges, plywood needs edge treatment, plasterboard needs jointing and taping.
4. Emissions. Indoors, the formaldehyde class matters, particularly over large areas in small rooms.
5. Fire. In escape routes and plant rooms the reaction-to-fire class governs the choice; plasterboard and fibre cement score far better than wood-based boards.

Working tips

• Let boards acclimatise in the room where they will be fitted, laid flat on battens, before fixing.
• Allow for movement. Wood-based boards move; leave a few millimetres between boards and at abutments. Boards fixed tight will buckle.
• Stagger the joints of the second layer against the first; aligned joints are the first place cracks appear.
• Fix at the right spacing per the system or manufacturer instructions: too far apart leaves loose edges, too close to the edge tears the board out.
• Cut with extraction and a dust mask. MDF and fibre cement dust is fine and does not belong in your lungs.

Related terms

• Plywood
• OSB board
• MDF
• Plasterboard
• Framing

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