Barrier membranes create fully functional basement

Context

Westminster City Council's planning department granted The Portman Estate planning permission in 2015 to redevelop the 90,000 sq ft site of the old Marylebone Police Station at 1-9 Seymour Street to create a new 7-storey mixed use building which would include a two level basement.

Delta Membrane Systems worked with the basement specialists Guardian Preservation to give expert advice during the planning stage and ensure a fully functional waterproofed basement for the building.

The basement dig was planned with the use of contiguous piling in conjunction with an inner RC lining wall.

After site analysis and assessment of ground conditions, Guardian Preservation gave careful consideration to products available that would be best suited to the project and ensured that all Building Regulations, including BS8102:2009, were adhered to.

Products used

All construction joints were appropriately detailed and waterproofed using hydrophylic waterstops – such as Koster Quellband, which expands in contact with water to seal the construction joint.

Delta Membrane Systems Ltd's Köster NB1 in-depth migratory crystalline slurry (a Type A system, a water barrier), and Delta MS500 and Delta MS20 (a Type C system, cavity drain membrane system) were used.

Köster NB1 has a capillary plugging agent ideal for sealing against pressurised water (> 13 bar) and is watertight (>130m water head). It also has excellent resistance to pressure and abrasion as well as chemicals. The product was applied with a peristaltic pump providing an efficient, uniform spraying application.

A secondary Type C system was then applied to create a robust waterproofing design.

The Delta MS500 premier cavity drain membrane was used for the waterproofing of the walls. It was fixed using Delta Qwik-seal plugs, at 600mm centres, with added benefits of Delta double-sided butyl tape to seal joints and overlaps. Delta butyl Corner strip tape was added to seal wall/floor joints.

The Delta MS20 heavy gauge cavity drain membrane was used for waterproofing the floors incorporating 20 mm studs which offered extra drainage capacity. The membrane was used as a “cavity former” for this construction. It was neatly rolled out across the basement floor; the sheets were overlapped and sealed in accordance with the manufacturer’s instructions.

Corner strip tape was then added to seal wall / floor joints.

Outcome

The basement has been constructed to cope with any future water ingress and will withstand the test of time. The project was achieved on time and within budget and Galliford Try was very happy with the outcome.