All pipework must be supported to prevent rattling. Remember also that regular movement of pipes will cause stress on the joints, which may eventually lead to failure.
When the work is being run along the surface, it is relatively easy to provide support by fitting pipe clips at regular intervals. There are many different types available. The easiest types allow the pipe to be snapped into place or removed without the need for removing the clip.
Pipes below floors - support at joists
When running pipes beneath floors, the joists can be used to provide support when the pipes run across them. When pipes are run parallel to them however, they will need to be clipped to the joist. When notching-out joists to accommodate pipes, make sure that the notch is deep enough to avoid the boards fouling the pipe when they are relaid. Remember, however, that each notch will weaken the joist so do not make them unnecessarily deep. The width of the notch should be a little wider than the pipe, so that it will not rub against the joist as it expands and contracts with changes in temperature. The position of a pipe should be under the centre line of the floorboard covering it. This will enable the board to be relaid and nailed both sides without piercing the pipe.