Floors: ideas for platforms
Changing the level of a floor can be an effective way of demarcating an area for a specific purpose, a dining area in an open plan living room for instance. Changing levels usually means a platform of some sort, but the area singled out doesn’t have to be higher than the rest of the room. By raising the floor in the one part you can create the impression of a well elsewhere which is actually at normal floor level.
Whenever floor levels are altered, you’ll need to give some thought to the skirting boards and also door thresholds and remember to retain sufficient headroom. If you create a gallery floor you’ll probably need enough headroom to stand above and below the new floor.
There are various ways to construct a raised floor. The method to choose mostly depends on the area and height of the platform and on the type of sub-floor which you might find below.
The spacing for the supports is decided by the floor decking. Flooring- grade chipboard 18mm thick is used most often. For this the supports should not be more than 600mm apart. As a rule of thumb the depth of timber should not be less than one tenth of the span between supports. To avoid damp or damaged timbers, air should be able to circulate beneath the raised floor. When using solid supports, such as joints laid directly on the existing floor or a chipboard box or egg- crate, drill holes with a diameter of 25mm or so for ventilation.
Most platforms will need wall- plates for edge support – use timbers 75mm by 50mm firmly plugged to the wall. Don’t hang a raised floor on a wall lined with plasterboard. Build an edge support instead. On a solid floor this can be a small brick or block wall.
Chipboard box
Separate boxes of 18mm chipboard are particularly useful for steps, but can be used for a low platform over wider areas. The corners are butt- jointed and strengthened with 25mm square battens glued and screwed into place. Use on solid or suspended floors. Can be freestanding.
Eggcrate
A very sturdy platform can be created from lengths of 18mm chipboard or softwood planks joined together with half-lap joints – see drawing. The joints are usually glued for extra strength. Useful for low platforms over small or large areas. Use on solid or suspended floors. Can be freestanding.
New joists
Joists (new or perhaps sound secondhand ones) can be suspended from hangers fixed into the masonry joints of opposite load-bearing walls. In this situation they will take the full load that was on the existing floor and must be sized to suit this purpose. This method is useful for a fairly high-level platform in a room which is not too wide. One of the other platform construction methods such as the chipboard box can be used to create steps up if required. Joists can also be laid directly on the existing floor. In which case smaller timbers can be used though this obviously creates a lower platform. The joists could be held in place by skew-nailing into waliplates.
Timber stud
Lengths of softwood 75mm by 50mm can be used to create short timber stud walls. Timbers can be joined with glued and nailed half- joints, or simply skew-nailed. The bottom plate is fixed to the existing floor. Can be used on suspended or solid floor, but on a solid floor the brick honeycomb wall method is probably easier.
Brick honeycomb walls
On a solid ground floor the support for a new floor can be provided by sleeper walls constructed of bricks bonded in an open honeycomb like the sleeper walls for a suspended timber ground floor. To provide a fixing for the floor covering, a framework of 50mm by 50mm sawn softwood is bedded in mortar on the brick walls. For walls which are a little cheaper to build, one or two courses of bricks can be built on edge, but for platforms higher than 250mm the walls are more stable if they are constructed with the bricks the correct way up.
A gallery floor
A gallery in a high-ceilinged room can be constructed: as a new floor on joist hangers; as a timber framework taking its support from posts to the floor and the adjacent walls or as a freestanding structure of scaffold tubes. The design is peculiar to each situation and as you’ll be adding to the load on the existing floor and walls professional advice is useful, if not essential.
