To ask the Secretary of State for Environment, Food and Rural Affairs, what estimate she has made of the comparative costs of (a) connecting new minor developments to surface water main drainage and (b) utilising sustainable drainage systems for such developments in the next five years.
Defra Research & Development project WT1505 provides estimates of the comparative costs of sustainable drainage (SuDS) versus conventional drainage (to Building Regulations) for a minor development as follows:
(<0.2ha, 8 properties, 1 outfall)
Capital (construction) costs
Maintenance costs (per annum)
Cost estimate (SuDS: “normal” permeability)
These estimates relate to what the research classed as “normal” permeability.
Using SuDS on sites with different permeability levels could incur higher or lower construction and maintenance costs. However, under the Government’s approach there is a presumption that conventional approaches to drainage can be used where construction costs would otherwise be higher.