Most old houses in Britain have suspended wooden floors (also known as hollow floors) in ground floor rooms. However, during and after World War II, wood became scarce and restrictions were placed on its use and availability, so other forms of construction were employed. Solid flooring was introduced as a suitable and economical alternative to ground level.
suspended wooden floors
A suspended wood downstairs consists of a series of boards, sometimes tongue-and-groove, or sheets of man-made boards, such as chipboard or plywood, laid over and supported by wooden joists. The beams are spaced 400mm to 600mm apart and are supported by 100mm x 50mm timber wall plates which are in turn supported by the main walls of the building, or by sleeper walls constructed of one layer of concrete under the house, or by a combination of the two. To prevent the wooden floor from absorbing moisture, the wall plates are placed on top of a suitable waterproof layer.
Suspended Wood Upper Floors
Like the lower suspended floors, the upper floors consist of wooden boards or handmade sheets of boards placed on and supported by wooden beams. Suspended wood floors that are not at ground level are often referred to as single floors because the joist bridge has a single span that runs from wall to wall.
Since it is not possible to give additional support to the upper floors by using cross tie walls, the beams of the individual floors are larger than those of the hollow lower floors and generally join the narrowest span, often through the narrowest part of the room. If the spans of the joist bridge exceed 4.0 m, wooden or steel cross members (called binders) can be used to provide intermediate support. Single-story joists tend to flex, so rows of struts can be placed across the floor between the joists to make the floor more rigid.
The ends of the joists may be embedded in the walls or supported by embedded joist hangers or attached to the face of the wall. If the end of the joist is built into the wall, this part should be treated with a preservative to protect it from decay.
The ceiling in the room below the floor is usually lath and plaster or plasterboard attached to the bottom of the joists. The sheetrock may have a “skim” plaster finish.
solid ground floors
The cross section of a solid floor consists of several layers of different materials.
The first layer is 100 to 150 mm of hard consolidated composed of crushed stone and clean broken bricks. This is to level any unevenness in the ground caused by the excavation and provide a firm, level base for the floor slab.
A 50mm thick layer of fine ash, sand or weak concrete mix is placed on top of the hard core to bond the surface. This blinding will also provide a smooth and even surface to place the waterproof membrane. The waterproof membrane should never be placed directly on the core, as it could be punctured.
The waterproof membrane can be placed above or below the floor slab. In the latter case, the DPM will keep the floor slab free of moisture. A wide range of materials are suitable as DPM: hot and cold poured bitumen, asphalt, epoxy pitch compounds, and 1000 gauge polyethylene sheeting.
The floor slab (concrete) can vary in thickness from 100 to 150 mm and have one or two layers of reinforcing mesh, depending on the area of the floor and its intended use. The concrete slab may have a layer of cement placed on its surface, depending on the type of floor finish to be used.
To provide additional insulation, 50mm sheets of expanded polystyrene can be added between the slab and the screed.