5.4.9 Buried podiums
Buried podiums shall be protected by adequate waterproofing and drainage.
A buried podium forms a below ground roof to an area of basement that extends beyond the outline of the main building or buildings above. The waterproofing layer must link with damp proofing in any abutting walls. In most cases, the waterproofing should extend to DPC level or a minimum of 150mm above finished external ground level.
The make-up of the waterproofing layer and subsequent toppings that could include sustainable green, biodiverse (brown) or blue roofs, and provisions for drainage, should be co-ordinated at the planning stage. Guidance on the design, detailing and construction of sustainable roof and associated drainage systems (SuDS) is covered in Chapter 7.1.
Provisions should be made to ensure the waterproofing layer and drainage system will not be susceptible to damage or obstruction from tree/vegetation root activity or structural movement. Drainage design should prevent ponding or accumulated/retained water unless part of a proprietary rainwater attenuation system (also see below).
Structural designs should allow for loadings from emergency, maintenance or other vehicular traffic access, mature planting/trees and/or saturated ground, as applicable. Further allowance should be taken of accumulated/retained water where blue roofs are adopted, or it is otherwise predicted by design (but kept to an absolute minimum), for example in the case of a drainage system temporary service fault or blockage prior to overflow provisions, land drainage or another water relieving strategy becoming active.
Last updated: 2nd January 2024