In an ideal world you would apply and external membrane and a perimeter land drain but this involves extensive digging. The land drain needs to be well below the level of the basement floor. Cellar waterproofing is something that requires meticulous care. Water will find its way in through one badly made joint. The most common of these is where the walls join the floor. If the building perimeter can't easily be drained below the internal floor levels with land drains then it is advisable to set up an internal perimeter drain. This requires a sump to be dug and a pump to be installed. The perimeter drain collects any water which penetratethe walls or leaks at the perimeter and it is then carried around in plastic channels to the sump.

In one of the featured basement shown here, the guys from North and South Basement Conversions have covered the walls with silver foil membrane from Wykamol Ltd. This not only stops damp but reflects radiated heat back into the room. The air gap between the membrane and the plasterboard must be at least 25 mm to make the insulation effective.

Studded membranes are fixed to the wall with hammer in plastic plugs which have mastic seals behind the head. The studs on the membrane allow the water to track down the back to the floor. The floor is also covered with a membrane which can be screeded over with a reinforced screed or overlaid with an insulation layer and chipboard. You need to take advice on the effect of the water table on the floor if you decide to seal it with a membrane and concrete rather than a studded membrane because a substantial weight of concrete is often required to stop the floor floating up as the water table rises. If this seems farfetched remember that racing yachts are often made with concrete hulls. Concrete will float if there is enough water under it.

All this waterproofing and concreting will of course require extra height and often the ceiling height is not adequate in the first place. Almost invariably a cellar conversion starts with a dig out. As this can be more than 300mm deep getting rid of the rubble and earth can be a laborious task.