Basements for housing

Domestic basements can aid in the creation of desirable, sustainable homes, providing greater flexibility and adaptability of space; thus extending the design life of the building. Including a basement maximises usage of available land, provides a stable construction base and improves thermal efficiency. The added value and space is most efficiently provided as part of a new build construction. Refurbishment or alterations to existing spaces below ground are also an effective way of providing additional habitable space to a property. It is possible, to retrofit a basement under or adjacent to an existing property.

Basement construction

Concrete is the most common and appropriate material used in the construction of new basement walls and floors. This is due in part to cost and availability but also its adaptability, inherent resistance to water, durability under ground and ability to provide a stable structural surface for the support of waterproofing membranes. With good detailing and workmanship, concrete can provide inherent water resistance, further enhanced by the introduction of admixtures.  A list of appropriate concrete construction methods can be found in the Basements for Housing publication published by The Concrete Centre.

Benefits

There are many reasons for the provision of basements in a housing development including: added value; increased development potential; occupant or purchaser attraction and sustainability.

Desirable and adaptable spaces

Basements can provide comfortable day-lit rooms, with natural ventilation and external access, as an extension to the living spaces above, but also provide the opportunity for more unique uses such as gyms, music rooms and work places.  One of the major benefits of basements is allowing the creation of a single large space. Due to economies and method of construction, the floor above the basement level can be created in a single span, providing flexibility in the location of internal walls and allowing simple future alterations.

Sound insulation

Good acoustic attenuation is provided by the concrete walls surrounding basement rooms, by the earth itself and significantly by the ground floor if constructed in concrete. Basement spaces are therefore inherently ideal location for noisy activities or to provide quiet spaces separated from the rest of the home, such as home offices.

Energy efficiency

Subterranean spaces benefit from the insulating properties of the surrounding ground, improving their energy efficiency. As a consequence, the amount of insulation needed to reduce heat loss through a basement wall is less than that required on upper floor levels. Studies by The Basement Information Centre (TBIC) and BRE highlight a potential 10 per cent saving in space heating for a two-storey house with a full ground basement compared with its three-story equivalent above ground (both having the same amount of added insulation). The potential space heating saving rises to around 14 per cent for a single storey property with full basement, compared to its two-storey equivalent above ground.

Thermal Mass

The heavyweight nature of basement construction can be utilised to naturally regulate the internal temperature of a home and can be part of an energy efficiency strategy for controlling the temperature of the whole house. The thermal mass properties of concrete are optimised by omitting insulating internal surface finishes. If insulated and waterproofed externally, basement concrete walls will offer greater thermal mass. This could be achieved with a fair-faced or painted finish, or alternatively a wet plaster finish.

Airtightness

The construction of sustainable dwellings using low air permeability and mechanical ventilation with heat recovery, such as Passiv Haus technique, is a means of improving the energy efficiency of the building fabric of dwellings. This is simply provided by basements, since the structure below ground is inherently more air tight.

Sustainability

Many of the fundamental principles of sustainable design can addressed through the provision of a domestic basement, including energy efficiency, longevity and adaptability of the property and support of local employment through home working potential.  Additional space can be provided for the storage of waste for recycling, alternative fuel supplies or other equipment associated with renewable energy or water recycling.

In addition basements can provide additional floor space without increasing the building footprint or significantly reducing garden size. For new build design the reduction in footprint relative to number of stories scores points in the Ecology Section of the Code for Sustainable Homes. A full list of how basements can assist with obtaining credits for the Code for Sustainable Homes can be found in the The Concrete Centre publication Basements for Housing.

Stable building stock

Basements create a good stable structural base, capable of supporting heavy loads above. By combining foundation design with the provision of habitable space, the extra depth of structure provides the building with greater ability to cope with climate change affects in the soil, such as shrinkage or tree roots.  Further more the construction of concrete ground structures or sacrificial basements is a recognised solution for construction in area of high flood risk, raising habitable spaces above the level of flood design risk, while providing useful non-habitable storage space. 

Basements design

The appropriate design of basements is well established and achievable providing design and construction guidance is implemented.  Design principles are summarised in Basements for Housing with a list of further design guidance. The forthcoming publication ‘Guide to the Design and construction of concrete basements’ provides comprehensive guidance on the design issues for the design of deep basements, focusing on structural calculations.