Down is the new up.
The trend has taken hold in London and other pricey towns and cities as the rising cost of property and the higher costs of moving have brought a new form of inertia to the housing market.
People can no longer afford to keep moving up the housing ladder by moving to a new house, so extending the current house is seeing much more activity.
Having already exhausted options for loft conversion and ground floor extensions where they can, homeowners in well-to-do streets, particularly in London, are calling in the diggers to utilise the space beneath their homes.
This makes more financial sense in the most expensive areas where the housing stock is limited and for those where moving is beyond their financial reach but digging down is now an option driven by ever increasing house prices and costs of stamp duty at the upper end.
This is now presenting problems for the insurance industry. Basement conversions are technically difficult jobs with the scope for lots to go wrong. In a competitive market building contractors without the specialist knowledge may be competing for such work.
Cellars were standard in many pre-war homes, but they are usually omitted in modern builds due to the time and expense of their construction. So, it is important to remember that cellar or basement conversions are often taking place in older properties that may have suffered settlement of subsidence/heave over the years and may have been altered, which can compromise the structure e.g. new door/window openings, walls removed, chimney breasts removed etc.
Basement conversions can take several forms:
- Nonstructural conversion — where there is absolutely no structural alteration, and the work is just a “cosmetic” refit then this can be acceptable. However, this is generally rare as people are looking to maximise space and any basement fit for use without structural alteration is probably already being used.
- Structural conversion — to an existing basement within the footprint of the property. Basements often lack head height and in older properties will often have been built as a storage area of less than the full footprint of the ground floor or may be subdivided by supporting walls.
- To make additional head height often requires digging down, which will expose and potentially weaken the foundations, or often goes below the level of the existing foundations requiring strengthening and underpinning. This is a highly skilled and specialist job.
- Removal of supporting walls — people are often looking for an open plan basement area rather than a labyrinth of small, subdivided rooms. So, supporting walls need to be removed, propped and supported with steel beams. Again, this is a highly skilled and specialist job.
- Creation of a basement — some houses that were never built with basements are having the foundations dug out to create additional room below the property. This can increase the risks noted above as it will often have to go some way below the existing foundations.
- Extending below and beyond the footprint of the property — Super conversions — these are rare but there are multimillion-pound conversions which go beyond the footprint of the building and down several storeys to offer home cinemas, swimming pools or domestic staff living quarters. The risks associated are extremely high.
- Subterranean Storage — A recent development in the form of ‘Plastic Cellars’ is making installing a cellar an option for those requiring additional storage space. Plastic cellars are insulated underground storage units which are placed under the garden to allow for storage without taking up limited garden space with large sheds or garden rooms. Excavations required can be deep and close to buildings. So, while not the same risks as digging below a property it still presents risks of removal of support and damage to underground services. The plastic cellar then needs to be winched into place which often means lifting it over the house by crane. Not an insignificant risk.
There have been recorded occurrences of houses collapsing during or following a basement conversion.
Total collapses are rare, but there is a much higher occurrence of minor damage/cracking which can still cost a great deal considering the types and values of properties involved. Some sort of settlement is almost inevitable after major structural work. While this is often a cosmetic repair rather than major structural damage, the costs can still be considerable.
Basements and Flood
Basements can suffer from damp issues and are much more susceptible to flooding and the backing up of sewers. With flash floods becoming more commonplace, basements can be the first hit.
Summary
Basement conversions can be technically complex jobs, requiring specialist contractors and appropriate insurance should be put in place before any works can begin. A number of insurers are now also including basement flood exclusions as standard on property policies, or imposing additional terms based on their flood mapping tools, so it’s worth bearing this in mind when undertaking any kind of policy comparison.
Note: Information detailed in Technical Talks has not been verified for accuracy by a third party. None of the information should be taken as legal or professional advice.