Before constructing any partition, the type of floor that you are building onto is always an important factor.
With a solid floor, the partition can stand anywhere, (assuming that the floor does not conceal underfloor heating or pipework), and fixed down using screws and plugs. In the case of a suspended wooden floor however, things can get a bit complicated if the floor joists are not in a position that would support the partition. The first thing that needs to be established is the direction in which the floor joists are running. If they are parallel to the proposed partition, then the position of the joists must be located, and if it is found that the partition would be positioned between two joists (over the gap) as shown in Fig 1, the floorboards in the area should be raised, and trimmers (short length of joists) introduced and fixed between the joists using joist hangers at 400 mm centres. This must be done to the full length of the partition as shown in Fig 2, and the illustration on the left. If the partition is to be positioned directly over a single joist, (to its full length), then this would normally be sufficient to carry the weight assuming that the width and depth of that joist is within the acceptable limits. If the joist in question does not conform to this requirement, then it would need to be reinforced, usually by spanning a second joist (supported from wall to wall) next to it, and bolting the two together as shown in Fig 3. If the partition and floor joists are running at right angles to each other, then this would be the ideal situation and should not present any problems.
Before work begins, checks should be made to ensure that there are no electric cables, water or gas pipes running along or across the joists in the path of the proposed partition, which could be damage in the course of construction.
In addition to being fixed to the floor, the partition must also be fixed to the ceiling, and the same principles apply regarding joist positioning. However, different to floor joists, things are simpler with ceiling joists if trimmers are required, as they can simply be nailed between the joists at 600 mm centres. This is because the ceiling trimmers are only required for fixing to, rather than supporting any weight. Again if the ceiling joists were running at right angles to the partition, then this would be the ideal situation. Their location should be marked; which will make things easier when it comes to fixing the head plate to them.