Wet rooms require an approved membrane, a fall towards the floor drain and an adhesive that suits the system. Here are the requirements from BR18 § 339, the guidance on SBi Guidelines 252 and the tile adhesive standard in one place.
Introduction
A leaking wet room is the most common type of damage in Danish construction. The requirements for wet rooms are in BR18 § 339 (chapter 14, Moisture and wet rooms), and SBi Guidelines 252 shows how they can be met. The approved waterproofing membrane and the tile adhesive are the two key products.
Floor fall and wet zone
| Parameter | Value | Status | Source |
|---|---|---|---|
| Fall towards floor drain | sufficient fall in the water-exposed part | Requirement | BR18 § 339 + guidance |
| Floor fall in general | min. 1 % (10 mm/m) | Indicative | SBi 252 |
| Fall under shower niche/bath tub | min. 2 % (20 mm/m) | Indicative | SBi 252 |
| Settlement in floor | max. 1 mm depth / 250 mm extent | Indicative | SBi 252 |
From percent to millimetre — how much the floor must be built up
The slope requirement is in percent, but on site it must be converted to millimetre build-up. A slope of 1 % means 10 mm per metre, and 2 % means 20 mm per metre — so from door to drain simply multiply the slope by the distance.
| Distance to drain | Fall at 1 % | Fall at 2 % |
|---|---|---|
| 1,0 m | 10 mm | 20 mm |
| 1,5 m | 15 mm | 30 mm |
| 2.0 m | 20 mm | 40 mm |
| 2,5 m | 25 mm | 50 mm |
Tile consumption is also affected by the pattern. With diagonal (45°) laying there is cutting along all walls, so waste is greater than with straight laying. Where straight laying is often calculated with a waste allowance in the order of 5–10%, diagonal laying is typically calculated with a larger allowance (often ~10–15%) — so order more tiles and keep track of colour/batch number so a reorder matches. The precise waste percentages are experience figures (advisory bricklaying practice), not code requirements.
Membrane and MK approval
The waterproof membrane must be MK-approved (ETA-Danmark) or ETA/TGA-documented. The system is ALWAYS used as a complete system: primer → membrane → adhesive → grout from the same approval. Corners and transitions are secured with sealing tape; penetrations with sleeves.
Tile adhesive — classification (DS/EN 12004-1:2017)
| Code | Meaning |
|---|---|
| C | Cement-based adhesive |
| 1 / 2 | Trækvedhæftning ≥ 0,5 / ≥ 1,0 N/mm² |
| S1 / S2 | Deformerbar / stærkt deformerbar (S1: 2,5–<5 mm; S2: ≥ 5 mm tværudbøjning) |
| T | Thixotrop / ikke-glidende (≤ 0,5 mm glidning) |
| E | Extended opening hours |
| F | Quick-hardening |
Movement joints and tile joints
- 01Elastic expansion joint in corners and transitions: width min. 6 mm, depth approx. 2/3 of width (BYG-ERFA, guide).
- 02Joint width tiles: 2–3 mm (small tiles) / 3–5 mm (large) / up to 10 mm (rustic, guidance).
- 03Membrantykkelse (smøre): typisk ≥ 1 mm, oftest 2 lag (leverandørens MK-godkendelse angiver kravet).
Wet zone division
A wet room is divided into zones according to how much water the surfaces are exposed to (SBi 252). The zone determines where the requirements are stricter and where the membrane must be at minimum.
- 01The floor — the entire floor is considered a wet zone; the membrane covers the entire floor and is brought up the wall with a cove base.
- 02Particularly water-exposed wall zone — at and around the shower/bath; how far the zone extends beyond the recess is determined by SBi Guidelines 252 and the system's MK approval.
- 03Other wet zone — the rest of the room's walls, where the load is lower, but there may still be water-tightness requirements.
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