A wide range of flooring grade of chipboards is available: ask a local timber merchant for information about the variations in surface finish, edge finish -and the size of sheets available. The sheet used most widely measures 1220 x 2440mm and is 18mm thick. It has either a square or tongued-and-grooved edge – the latter is the better of the two for flooring. Sheets of tongued-and-grooved chipboard are also available in widths which are likely to pass through the opening in a loft.
When replacing a suspended floor, the first job is to strip off all the original flooring and clean off the joists. The centre of the joists in houses are usually just over 405mm apart – convenient for laying 1220 x2440mm sheets. For joists more than 460mm apart, use 22mm board.
The next step is to provide support for the edges of the chipboard sheets by inserting noggings between the joists around the perimeter of the floor. If square-edged boards are used, it is necessary to insert noggings over the central part of the floor wherever the edge of a sheet will be unsupported.
The joins in the floor should be staggered to provide a stiff floor. The easiest and most economic way of doing this is to start every other row with a half sheet of chipboard and then use full sheets to fill in the rest of the floor area. Square-edged sheets should run with their longest edge along the joist. Tongued-and-grooved sheets should run with their longest edge across the joists.
When starting to lay the sheets, make sure that the joints between sheets will run along the centre of the supports (or joists) and will fit tight to one another. The sheet can be fixed either with lost head nails or with countersunk screws. Use 2in nails or screws for 18mm board; 2Jin for 22mm. Insert the fixings in a regular pattern from 200 to 300mm apart around all the edges of the sheets and from 400 to 500mm apart along the intermediate joists.
Think about access panels and traps in the floor for things like water taps and central heating pipes. These are best built into the floor when it is being laid -though small traps can be cut out afterwards with a padsaw. Position access panels so that two edges are supported by joists. Then fix noggings across the joists to support the other two edges. When the trap is cut out after the floor has been laid, screw a batten to each joist and insert noggings between them to support all four edges of the trap. Access panels and traps should be screwed in position so that they can be removed.
Once the floor is down, punch all the nails 2 to 3mm below the floor and make sure that all screws are sunk into the chipboard.
