Concrete @ your Fingertips

Basement grades and types

Construction of a basement has become common place, especially in urban areas where land costs are high.


A successful structure requires an understanding of design, construction and the resolution of many construction issues to ensure a suitable level of water tightness for the desired internal environment.


BS 8102: 2009 Code of practice for the protection of below ground structures against water from the ground defines 4 Grades of basement;

  1 - basic utility (car parking, plant rooms (excluding electrical equipment), workshops)
  2 - better utility (workshops and plant rooms requiring drier environments than Grade 1)
  3 - habitable (ventilated residential and commercial areas)
  4 - special* (archives, requiring controlled environments)


*Note that the 1990 edition of BS 8102 made reference to Grade 4 (Archive storage). This is the same as Grade 3 but with higher performance level for ventilation, dehumidification or air conditioning.


BS 8102 also defines 3 Types of water-resistant construction; 

   A Barrier (Membrane) protection
   B Structurally integral protection
   C Drained protection


There are various Forms of construction to achieve levels of watertightness;

  Reinforced Concrete box
  Contiguous/secant piling with facing wall
  Diaphragm walling


These need to be constructed in conjunction with specific vapour exclusion measures, depending on the environment required, typically:
  Drained cavity
  External membrane
  Internal membrane
  Active precautions (heating and ventilation systems)


Concrete Basements. Guidance on the design and constrcution of in-situe concrete basement structures, MPA, 2012

Basements: Waterproofing. General Guidance to BS 8102:2009, Basement Informtion Centre, Camberely, 2011 

Acknowledgement: Concrete Society