This may not present the most in-date information or product specifications available, but the idea is to obtain a greater perspective on basement construction. Such methods should also be seen to represent both residential and commercial basement construction technology. London is experiencing a basement boom and this boom has led to prevalent use of commercial techniques in residential construction, such techniques were once considered typical for larger commercial construction projects. One of the main, current, criticisms of the Party Wall etc. Act 1996 is it’s inability to handle such demanding projects.
Water resistant, not water proof basement construction
Basement waterproofing is a somewhat incorrect term, resisting the water pressure into the basement construction is for the most part an impossibility. What is possible is providing ways to mitigate water infiltration.
Water Resisting Construction
Several sources propose three different waterproofing techniques, referred to as Type A, B & C.
- Type A (Tanked)
Water protection is afforded by a membrane or barrier. Somewhat more substantial than what you would expect to find in a typical domestic concrete floor slab or damp proof course. Such water proofing can be provided internally or externally. Materials can be bituminous bonded sheet membranes to BS 743:1970, Class A or BS8747, liquid applied membranes, geosynthetic (bentonite) clay liners, mastic asphalt membranes to BS EN 12970, cementitious crystallisation slurries and powers or cementitious multi-coat renders, toppings and coatings.
- Type B (Integral within Structure)
The structure itself forms a water protective barrier, continuity of the barrier is provided by water bars or water stops which need to accommodate for physical and differential movements.
- Type C (Drained Cavity)
Where water is expected to infiltrate the construction a second masonry skin is built inside the basement, this allows space for a cavity which drains water to a sump. A water pump will then remove the water out of the building.