Basement and Cellar Conversion

Cellar Waterproofing

Old cellars and basements will usually require waterproofing if they are to be used as habitable areas. Two methods of waterproofing are commonly used, the choice of which will depend on a number of factors such as the condition of the underlying substrate (e.g. are the bricks soft and powdery?), the practicality of incorporating a sump and pump, and the condition or existence of the floor slab. These systems are described below:

The Vandex Waterproofing System

Vandex waterproofing slurries are applied to the walls and floors of the cellar. Once cured, these prevent moisture from entering the cellar. Because the Vandex system relies on physically preventing water from entering the cellar it needs to form an extremely strong bond with the substrate that it is applied to. For this reason, careful preparation of cellar walls and floors is essential prior to the application of the Vandex system.

The Oldroyd Cavity Drainage System

The Oldroyd cavity drainage system is based around a "dimpled" plastic membrane that is applied to the walls and floors of the cellar, creating a "drainage cavity" which redirects moisture entering the cellar to a sump and pump. Because the Oldroyd system redirects water, rather than physically holding it back preparation of the substrate is less critical than when using the Vandex system.

The Importance of Ventilation

It is important to note that a waterproofing system alone can only achieve a Grade 2 environment as to achieve a Grade 3 environment control of the level of relative humidity in the air of the cellar or basement is required (in order to reduce the risk of dampness caused by condensation). Old cellars rarely benefit from high levels of natural ventilation, so it is likely that some kind of additional ventilation will be required to reduce levels of relative humidity. Additional ventilation can take the form of air-bricks, humidity controlled fans, and heat exchange units. Your specialist cellar conversion contractor will be able to advise on the most appropriate form of ventilation for your cellar.

Grade Basement Use Performance Level
1 Car Parking; plant rooms (excluding electrical equipment); workshops. Some seepage and damp patches tolerable, dependent on the intended use. Local drainage might be necessary to deal with seepage
2 Workshops and plant rooms requiring a drier environment; retail storage areas. No water penetration acceptable. Damp areas tolerable; ventilation might be required.
3 Ventilated residential and dryness that are working areas including offices, differing required for restaurants, etc.; leisure centres. basement uses. No water penetration acceptable. Ventilation, dehumidification or air conditioning necessary, appropriate to the intended use.

Adapted from BS8102:2009 - Table 2

Increasing Light in Cellar Conversions

For some cellar conversion projects (e.g. where the cellar is to be used as a home cinema) a lack of natural light can be seen as an advantage. However most people commissioning a cellar conversion project will want to investigate ways of increasing the level of natural light entering the cellar. There are a number of methods of achieving this aim, including:

Additional Windows

Additional Windows

The top part of some cellars is actually above-ground on one or more walls, so adding additional windows can be a simple option.

Light Wells

Cellar Light Wells

A short trench is dug alongside one of the basement walls and a window installed. The trench will need to be constructed and waterproofed to the same standards required for a newbuild basement.

Glass Doors

Glass Doors

Where a cellar has an entrance from the outside, the use of a toughened glass door can be considered.

Light Tubes

Light Tubes

The Monodraught Sunpipe shown in the diagram on the right redirects light from ground level into the cellar through a reflective pipe.

"Dig Out" Cellars and Garden Basements

It is possible to increase the size of an existing cellar to the size of the footprint of the entire building and even to construct a brand new cellar underneath an existing building. Such projects require careful structural calculations and specialist underpinning techniques so they should only be undertaken by experienced contractors. Because of the additional work involved, "dig out" projects usually cost upwards of £100,000, however in areas of the country where property prices are high this cost can often be compensated for by a corresponding (or greater) rise in the value of the property.

It is also possible to extend cellars and basements underneath gardens. This is a great way of increasing living space without reducing outdoor amenity space.

Cellar Conversion Contractors

Because of the knowledge and skills required to carry out a cellar conversion most cellar conversion projects are carried out by specialist contractors. Many specialist contractors are members of the BSWA or PCA Structural Waterproofing Group enabling them to offer insurance-backed guarantees on cellar conversions that they carry out. For details of such contractors in your area please call 01403 210204 or use our enquiries form.

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