Wet Room Tanking Calculator — Waterproofing Materials Needed

Our wet room tanking calculator works out the total area to be waterproofed (floor plus walls to your specified height), then calculates the tanking liquid, reinforcement tape and corner pieces you need.

The formula

Total tanking area = Floor area + (Sum of wall lengths × Tanking height)

Tanking liquid = Total area × Coverage per coat × Number of coats × Wastage factor

We default to 0.5 L/m² per coat × 2 coats = 1 L/m² total — the upper end of the realistic range. Most liquid membranes use roughly 0.7–1 L (or kg) per m² for the complete two-coat system: Mapei Mapelastic AquaDefense is about 1 kg/m² over two coats, and Weber webersys protect about 0.8 kg/m². Coverage varies by product, so set the per-coat figure from your chosen product’s Product Data Sheet using the advanced options.

What you need

• Tanking liquid: Roughly 0.7–1 litre (or kg) per m² for the complete two-coat system (about 0.4–0.5 per m² per coat), with 2 coats required. Common products include BAL Tank-it, Mapei Mapelastic AquaDefense, Weber webersys protect and Everbuild/Sika Aquaseal — always confirm the exact rate on the product’s data sheet.
• Reinforcement tape: Applied to all internal junctions (floor-wall and wall-wall corners) and embedded in the first coat of tanking liquid. Typically sold in 10m rolls.
• Internal corner pieces: Pre-formed corner pieces for wall-wall vertical junctions and floor-wall corners provide additional waterproofing reliability.

Building Regulations

Wet room waterproofing must comply with Building Regulations Approved Document C (resistance to moisture) and follow BS 5385-4:2015 (design and installation of tiling in wet/damp areas, clause 7 covers frequently-wetted conditions). The tanking system must form a continuous, sealed membrane across the floor and up the walls. All pipe penetrations, drain connections and corners must be sealed with compatible products from the same system.

Our default coverage rate is taken from leading UK tanking-system Product Data Sheets, but consumption varies between products (roughly 0.7–1.25 L/m² total over two coats), so set the per-coat figure from your chosen product’s data sheet for an exact result. We recommend adding 10% wastage for application losses and brush-on variability.