Wet Room vs. Standard Bathroom: Which Is Right for Your Renovation?

• **Standard bathroom**:
• •Contains a discrete shower area — either a shower tray with glass enclosure, or a bath with a shower over it
• •The floor outside the shower area is finished in ceramic or porcelain tile on a standard screed or mortar bed
• •Only the shower area and bath surround are fully waterproofed to BS 8000 Part 1 Appendix A standards (Zone 1 — the area directly wet)
• •Water containment depends partly on the shower tray and enclosure

• **Wet room**:
• •No discrete shower enclosure — the shower head (typically a wall-mounted or ceiling rose) drains directly to a floor drain
• •The entire floor (and walls to a minimum height, typically 2.0–2.4m) must be fully waterproofed
• •The floor must be laid to a fall of typically 1:80 (12.5mm fall per metre of floor) toward the drain — on a concrete slab, this is straightforward; on a timber floor, the fall must be formed in the screed
• •Water management relies entirely on the waterproofing system and the drainage fall — there is no tray to contain water

• **When a wet room makes sense**:
• •Very small bathrooms (under 4m²) where a separate shower enclosure would feel cramped
• •Loft conversions with sloping ceilings where a standard shower enclosure cannot be installed
• •Accessible or future-proofed bathrooms (level-access shower for mobility needs)
• •High-end refurbishments where the open, seamless aesthetic is desired

• **BS 8000 Part 1 — the waterproofing standard**:
• BS 8000-1 sets out the minimum waterproofing requirements for wet rooms and shower areas. For a wet room:
• •The entire floor and walls to at least 2.0m height must be waterproofed to Zone 1 standards
• •The waterproofing system must be continuous — all junctions between floor and wall, at pipe penetrations, and at drainage outlets must be fully sealed

**The primary waterproofing systems**:

• *Liquid-applied membrane (the most common residential system)*:
• A polymer-modified cementitious or acrylic liquid is applied by brush or roller to the substrate in multiple coats, building up a continuous seamless membrane. The tiles are then bonded to the membrane with a flexible waterproof tile adhesive.
• •Advantages: fast to apply, no heat or specialist tools needed, widely available, suitable for most substrates
• •Common products: Mapei Mapelastic, BAL Tank-It, Schlüter KERDI (sheet membrane applied with the liquid)
• •Application: typically 2–3 coats with fabric reinforcement tape at all junctions; full cure time of 24 hours minimum before tiling

*Tanking slurry*: A cementitious slurry applied to walls and floors — typically used for below-ground applications (basements) rather than bathrooms, as it is rigid and may crack at movement joints

*Schlüter Kerdi-Board + Kerdi-Band system*: A proprietary board-and-membrane system popular in high-end installations; the foam board substrate and KERDI membrane create a fully waterproofed substrate system with engineered drainage profiles; more expensive but highly reliable

• **Building Regulations**:
• A wet room (or any shower) is not notifiable work under Building Regulations in itself — the waterproofing is a workmanship standard, not a notifiable category. However:
• •If the wet room involves extending the drainage system (adding a new drain connection), this is Part H notifiable work
• •If the wet room involves moving or extending electrical supplies (adding or relocating a switched fused connection unit, extractor fan, heated towel rail), this is Part P notifiable electrical work
• •If the wet room is on a timber floor, the structural implications (trimming joists for the drain, forming the fall in the structure) may require structural engineer input

The most technically challenging wet room installation is on a timber intermediate floor — the most common scenario in London Victorian terrace and semi-detached houses, where bathrooms are typically on the first floor with a timber floor structure.

**The problem**: A wet room on a timber floor requires: 1. A fall of 1:80 to the drain — on a concrete slab, this is formed in the screed. On a timber floor, the fall must be formed either in the screed (which adds weight) or by feathering the tile bed, both of which require careful detailing 2. A continuous waterproof membrane over a substrate that moves — timber floors expand and contract with humidity and temperature; a rigid waterproofing system (tanking slurry) can crack at movement; a flexible membrane is essential 3. A drain that penetrates the floor — the drain connection must pass through the floor structure; trimmer joists are required around any floor penetration, and the drain connection must be plumbed to the below-floor drainage 4. Sufficient depth for the screed and tile build-up without raising the finished floor level excessively — typically 70–100mm of build-up (screed + tile bed + tile) is required, which may require the timber floor to be cut down or the door threshold to be raised

• **The weight issue**:
• A wet room floor on a timber structure adds significant weight:
• •50–70mm sand/cement screed: approximately 100–120 kg/m²
• •Waterproofing membrane and tile bed: approximately 10–15 kg/m²
• •20mm porcelain tile: approximately 40 kg/m²
• •Total additional load: approximately 150–175 kg/m²
• For a 4m² bathroom, this is approximately 600–700 kg of additional load. The structural engineer should confirm the floor joists can carry this — in older Victorian properties, floor joist sizing may be marginal.

• **Specialist wet room systems for timber floors**:
• Several proprietary systems address the challenge:
• •Schlüter Kerdi-Board drainage profile (Schlüter-KERDI-LINE): a low-profile drain that minimises the required screed depth
• •Pre-formed shower trays in tile-format that create the correct fall within the tray before tiling (Schlüter KERDI-SHOWER-T, Marmox wet room systems)
• •Wedi Board wet room systems: waterproof foam board with pre-formed falls bonded directly to the floor without a full screed pour

**London 2025 costs — wet room vs. standard bathroom**:

*Standard bathroom full renovation (supply of fittings by client)*: £6,000–£10,000 for a 5–7m² bathroom, including strip-out, plumbing, waterproofing of shower area, tiling, and second-fix M&E.

*Wet room on concrete slab*: £8,500–£14,000 for a 4–6m² wet room, including liquid membrane system to all walls and floor, floor former or graded screed, linear drain, floor and wall tiling. Premium systems (Schlüter Kerdi-Board throughout): add £1,500–£3,000.

*Wet room on timber intermediate floor*: £10,000–£18,000+, reflecting the additional structural work (trimmer joists, floor-level management), specialist drainage system, and heavier waterproofing specification.

Second-fix materials (sanitaryware, brassware, shower fixtures, mirrors, accessories) are client-supplied under RCB's standard terms. Budget separately for these: quality sanitaryware sets £800–£3,500, quality shower systems £500–£2,500, heated towel rail £150–£800.