Basement Review Draft policy and other measures for public consultation

Appendix A: Existing Policy

In December 2010 the Council adopted its Core Strategy. This included a number of policies that are specific to the consideration of new basement development.

Part (g) of Policy CL2, "New Buildings, Extensions and Modifications to Existing Buildings"

The Council will require it is demonstrated that subterranean extensions meet the following criteria:

i.  the proposal does not involve excavation underneath a listed building;

ii. the stability of the existing or neighbouring buildings is safeguarded;

iii. there is no loss of trees of townscape or amenity value

iv.  adequate soil depth and material is provided to ensure sustainable growth.

The supporting text reads

Para 34.3.20

Over the last five years, there has been a 70% increase in applications for subterranean developments, with over 200 planning applications submitted in 2008. Subterranean developments involve more challenging planning, environmental, engineering and construction issues than other conventional extensions. Given the high concentration of historic environments and assets within the Borough, controlling the impact of proposals for subterranean development is considered to be of strategic importance. Subterranean development may have minimal structural impact on the existing or adjoining buildings as long as they are designed and constructed with great care. The Council requires Construction Method Statements, signed by a Chartered Engineer or a Chartered Structural Engineer, to be submitted with all planning applications for subterranean development. These statements must set out clearly the potential impact, including cumulative impact, of the development on the existing, neighbouring or surrounding buildings, and the measures taken to mitigate these impacts having specific regard to ground conditions. Apart from the structural considerations, there is a particular concern regarding the impact of subterranean development on the special architectural or historic interest of listed buildings. In addition, to ensure subterranean developments do not add to the impermeable surfacing of the Borough, Sustainable Urban Drainage Systems (SuDS) or other measures will be required. This also allows the green nature of the Borough to be maintained.

Part (c) of Policy CE1, "Climate Change"

The Council will require an assessment to demonstrate that the entire dwelling where subterranean extensions are proposed meets EcoHomes Very Good (at design and post construction) with 40% of the credits achieved under the Energy, Water and Materials sections, or comparable when BREEAM for refurbishment is published.

The supporting text reads

Para 36.3.12

Planning applications for subterranean development in the Borough are increasing, with 64 in 2003, 89 in 2004, 85 in 2005, 110 in 2006, 192 in 2007 and 212 in 2008. This type of development produces a significant amount of greenhouse gases through the excavation and transportation of spoil, use of concrete, ventilation and lighting. It is right for the planning system to address this environmental impact. Given the nature of subterranean developments and the complexity of calculating and assessing CO2 emissions and savings, as a proxy the Council will take a pragmatic approach, using EcoHomes, to achieve energy savings across the whole of the original building. In most circumstances this will secure a substantial carbon saving, while will not penalising the owners of properties that alreadyhave a low carbon footprint.

Part (a) of Policy CE2, "Flooding"

The Council will resist vulnerable development, including self-contained basement dwellings, in Flood Risk Zone 3 as defined in the Strategic Flood Risk Assessment.