What Is Tanking? — Basement Waterproofing Explained

Definition

Tanking is the process of making a below-ground structure waterproof to prevent water ingress. The term traditionally referred to applying a cementitious waterproof coating (tanking slurry) to basement walls and floors, but it is now used more broadly to describe any basement waterproofing system. The UK standard for basement waterproofing is BS 8102:2022 - Code of Practice for Protection of Below-Ground Structures Against Water from the Ground.

When Is It Used?

Tanking is required whenever a habitable or usable space is created below ground level. This includes converting existing cellars into living space, constructing new basements, building retaining walls with habitable space behind them, and protecting underground plant rooms or storage. The choice of waterproofing system depends on the grade of waterproofing required (BS 8102 defines grades 1-3 based on intended use) and the site's hydrostatic conditions.

Key Facts

• BS 8102:2022 classifies waterproofing into Type A (barrier), Type B (structural), and Type C (drained)
• Type C cavity drain membrane is the most popular system in UK basement conversions
• Cementitious tanking slurry (e.g., Sika-1, Vandex) is applied in 2-3 coats to achieve 2 mm minimum thickness
• Cavity drain membranes (e.g., Delta MS500, Platon) have 8 mm or 20 mm studded profiles
• A sump pump with battery backup is essential for Type C systems
• Waterproofing design should be carried out by a CSSW (Certificated Surveyor in Structural Waterproofing)
• PCA (Property Care Association) members offer insured guarantees for waterproofing work
• Building Regulations require basement rooms to have adequate means of escape, ventilation, and insulation

Related Calculators

Use the Concrete Calculator for basement floor and wall quantities, or the U-Value Calculator for below-ground insulation design. The Sump Pump Calculator helps size pumps for cavity drain systems.