Concrete @ your Fingertips

Basement grades and types - BS 8102

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: 2022 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 construction of in-situ concrete basement structures, MPA, 2012 (based on 2009 Standard)

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

Grade 1 - car park
Grade 2- car park
Grade 3 - domestic

Acknowledgement: Concrete Society