Preparations: Floors of Small Buildings (DIY Small Buildings)

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In many buildings the floor and the foundation will be the same thing. A concrete floor is acceptable for many purposes. If you will be driving a car or a tractor over it or there is a risk of spilling oil or water on it, concrete should be the choice. If it's a workshop or other building where you will spend some time and might drop tools or equipment, a wooden floor is more comfortable and less liable to damage dropped tools. If it's a building for year-round use, a wood en floor gives a more equitable temperature underfoot. You can coat concrete with rubberized or plastic sealants that might give you ¼-inch of insulation and a more comfortable surface, but these are not as satisfactory as wood for long term standing.

figr. 1-6. A floor may be boards or particleboard on joists (A, B, C). Insulate wood from concrete (D,E). Conceal nails (F,G).

The usual wooden floor in a small building might be very similar to the floors in many houses, with boards laid over joists (figr. 1-6A). Sections of wood and spacing of the wood will depend on the size of the floor and the amount of support needed. As a guide, you can support boards which are 7/8 inch thick on 2- x -4-inch joists at 15-inch centers in an average small building (figr. 1-6B). In a very small building, the joists need only be 3 inches deep. Particleboard, at least ¾-inch thick, makes a good alternative to parallel boards. With joints on joists, you have the minimum of gaps (figr. 1-6C).

Avoid joists or other wood resting directly on concrete, brick, or stone. If you are supporting the ends of joists at wall foundations, insulate them from moisture (figr. 1-6D). This insulation might be material sold for damp-proofing, roof covering, or just pieces of plastic sheeting. If you intend to support the length of the joists by the concrete foundation, put strips of plastic under them or cover the whole concrete surface with plastic sheeting. It might be better to raise the wooden floor above the foundations especially if the concrete is not level in the main area. Even if the wooden floor starts apparently level, eventually it might take the uneven shape of the concrete below. A strip over damp-proofing might support the joists (figr. 1-6E) above the concrete. In some buildings, the bottom member of the wall might support the joists.

Punch nails through particleboard below the surface (figr. 1-6F). If you use plain boards, bring them tightly together and sink their nails below the surface. Better floor boards have tongue-and-groove joints. They will maintain a more even surface, which is important if you want to lay carpeting or other floor covering. You can conceal most of their nailing by driving diagonally through the tongues (F 1-6G).

One surprisingly hard-wearing floor covering is hardboard. In damp conditions, use the oil-tempered variety. Fasten it down with plenty of fine pins or nails. An initial wax spray or polish should seal it for life.

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Updated: Wednesday, December 8, 2010 16:00