Floor

Also called: flooring, floorboards, wood block floor, parquet

A floor is the walking surface of a room, built up from structural framing below and boards, blocks or strip flooring laid over it. The timber chosen for floorboards may be red deal or white deal (general terms for pine or fir timber, red and white marking different species), pitch pine, oak, birch, or maple.

Framing beneath the boards

Iron and steel girders see heavy use in floor construction, carrying the joists, the smaller timbers that span between them and support the boards directly. Joists can sit notched onto a girder and spiked down, which gives enough strength without needing to cut a notch into the girder itself, and ceiling beams can likewise be spiked securely without a slip mortise and tenon, a stronger but more elaborate joint that lets part of one timber slide into a socket cut in another. In Benson's (1988) approach to American post-and-beam timber-frame building, sizing each structural bent, a transverse frame of posts and beams repeated along the building's length, means weighing post length, beam height and rafter crossings against how the available floor space will actually be used. A chimney often needs no special floor framing in that same system, because joist spacing, sometimes up to 32 inches, already leaves room for it, though occasionally the flooring still needs extra support built in around a chimney. In timber-frame building of this kind it is sensible to lay the finish floor and ceiling over the structural timber floor, rather than leave the frame exposed as the finished surface.

Laying the boards

Modern floorboards are mostly planed, tongued and grooved, known as PTG, rather than square-edged, though square-edged boarding can still turn up in older buildings. A laid floorboard ends up roughly one-eighth of an inch thinner than its stated size, because both sawing and planing remove material. A floor nail should be about two and a half times the floorboard's thickness in length, while flooring brads, thin nails used for fixing floorboards, are supplied in a standard cut length regardless of board thickness. Flat-sided nails can be driven in parallel to the board grain without splitting the wood; because their heads run parallel with the grain too, they can be set beneath the surface with a punch, which lets the floor be planed later. Gluing the tongue-and-groove joints with PVA adhesive stiffens the floor and stops the joints moving; the tongue-and-groove joint itself turns up across woodworking generally, from laying floorboards to light cabinet building. Board edges running the long way do not need noggings, short blocking pieces fixed between joists, fitted under them for support, though it is best to nail fully over any pipe run while laying the floorboards, rather than trust memory or a later mark for the danger area. Insulating fibreboard can instead be laid as a layer sitting between the bearers, the timbers that carry the boards, below and the boarding above.

Grades, finishes and blocks set into the floor

A flooring machine's fixed cutters, called face irons, give the smoothest possible finish. In very expensive work, board ends can be cut with interlocking zig-zag notches whose ridges run parallel to the floor surface. Two-layer board construction is common in very superior floors, and a floor built up from two layers of boards this way is known as a Victoria Floor. Flooring of a given size, such as three-quarter inch, can also be cut from wider stock. Plain flooring, as opposed to the secret-nailed types, is face-nailed straight to the joists, leaving the nail heads visible. Quartersawn flooring, cut so the growth rings run close to upright through the board, has a silver or flaked grain figure that is often favoured over the figure seen in plainsawn flooring, cut the other way. USDA (2021) grading rules for US timber are written with the final consumer's intended use in mind, and the resulting US product categories include strip flooring with square edges and square ends, as well as parquet flooring, laid as small geometric blocks or panels, suited to mastic-laying, using a thick adhesive compound instead of nails. Blocks set into a floor end grain up, meaning with the end-grain surface, where the wood's fibres are cut across rather than along their length, facing upward, have the floor cut around them but are never fixed to them, so they stand independent of it. For a concrete floor, stone blocks bedded in concrete can be positioned before the concrete floor itself is poured.