Gaining headroom
Victorian and Edwardian cellars were built for coal, food storage and utilities, and they are often shallow. Lowering the floor increases the height of the space, so that it can be used as a utility room, home office, gym, living space or storage. It can be a way to add usable area without extending, but it is a significant structural operation.
What is involved
The floor of a cellar sits at or just below the base of the walls. Digging down means the foundations of the walls are no longer protected by the soil beside them. To keep the house stable, the walls are underpinned in short, controlled sections, usually in a set sequence, before the floor is excavated further. Only then can a new, deeper floor slab be formed.
- Survey of walls, foundations and the ground conditions
- Engineer design for underpinning and the new floor
- Sequenced underpinning in small bays, rather than all at once
- Excavation and removal of spoil, often by hand through limited access
- New concrete floor with damp protection and drainage as required
- Waterproofing of walls and floor
Waterproofing is part of the job
A deeper cellar is more exposed to groundwater, so lowering the floor is normally combined with tanking and waterproofing. A sump and pump may be needed in some locations. Drains that cross the cellar need to be considered, see underground drainage repairs.
Practical points
Access is often the main practical limit. Removing soil from a cellar under a terraced house can mean carrying it out in buckets or using small conveyors, which affects how the job is planned. Dust and noise should be expected, and the front or rear garden may be used for materials.
Permissions
Lowering a floor and underpinning are structural works that need Building Regulations approval. If you share a wall with a neighbour, the Party Wall etc. Act 1996 is likely to apply, since underpinning affects the foundation of the shared wall. Planning permission is often not needed for internal work, but check the Planning Portal, and see GOV.UK for party wall information.
Frequently asked questions
Is cellar floor lowering safe for the house?
Yes, when it is designed by an engineer and carried out in controlled stages. The risk comes from digging without supporting the foundations, which is why underpinning is done in sequence.
Will I need to tell my neighbour?
If the cellar walls are shared or the work affects neighbouring foundations, the Party Wall etc. Act 1996 is likely to apply and notices must be served. We can explain how this works.
