How to Build a Wet Room
in the UK

Section 1: What Is a Wet Room — and Which Type Do You Need?

A wet room is a bathroom where the shower area and in some configurations the entire floor is fully waterproofed and drains freely, without the need for a shower tray, enclosure base, or door threshold. The defining feature is the absence of a raised barrier at the entry point.

Beyond that basic definition, wet rooms divide into two quite different formats, and choosing the right one for your situation is the most important design decision you will make.

1.1 Two Types of Wet Room

1.2 The Small Bathroom Solution: Sunken Wet Room with Linear Drain

For bathrooms of around 3 m² — covering a significant proportion of UK en-suites and secondary bathrooms , a sunken (or recessed) wet room floor is the most practical and visually effective solution available.

The shower zone floor is excavated or built down by 30–50mm relative to the surrounding bathroom floor. This depression creates a natural boundary for the wet zone without any physical barrier. Water stays within the sunken area and drains freely, while the slightly elevated dry zone floor remains genuinely dry.

Pairing a sunken floor with a linear drain running along one wall — rather than a central point drain simplifies everything that follows. The floor only needs to slope in one direction, tile laying is straightforward, and the visual result is a clean floor surface with a single thin drainage line at the wall.

Structural considerations for sunken floors

• Ground floor (concrete slab): The most straightforward situation. The slab can typically be excavated to the required depth without structural implications.
• Upper floors (timber joists): Requires a structural assessment. Most UK timber floors built to modern standards have sufficient depth to accommodate a 30–50mm recess, but this must be confirmed before work begins. A building surveyor's assessment typically costs £150–£300.
• Upper floors (concrete): Generally more accommodating than timber but still require depth measurement before committing to a sunken design.

1.3 When a Wet Room Works Best

• Removing an unused bathtub. A bath typically occupies 1.7–1.9 m² of floor space. Converting that footprint to a wet room zone is one of the most efficient bathroom transformations available.
• Accessibility requirements. No threshold makes a wet room the most accessible shower format available. Pair with grab rails and a fold-down seat for a fully accessible setup.
• Modern aesthetic. The absence of frames, tracks, and trays creates a visual clarity that works well in small spaces.

1.4 When a Wet Room Is Not the Right Choice

• Upper floor with shallow joists — if insufficient depth for sunken floor or gradient, a conventional shower tray may be more practical.
• Households with young children — a fully open wet room floor means slippery surfaces throughout the bathroom.
• Rental properties — the higher build standard and consequences of waterproofing failure may not suit a rental context.

Section 2: Planning & Building Regulations

2.1 Do You Need Planning Permission?

For the vast majority of wet room installations, no planning permission is required. Bathroom renovation is considered permitted development under UK planning law. The exceptions are listed buildings and flats or leasehold properties where the lease restricts structural alterations, always check your lease before proceeding.

Building Regulations do apply to the following elements:

2.2 Key Dimensions & Design Standards

• Minimum shower zone: 900mm × 900mm (wet & dry zone); 1,000mm × 1,000mm (fully open wet room)
• Sunken floor depth: 30–50mm. Below 30mm — difficult to achieve required gradient. Above 50mm — becomes a trip hazard.
• Floor gradient: Minimum 2% (20mm per metre). See Section 3.2.
• Wall waterproofing height: 1,800mm minimum in wet zone; full ceiling height strongly recommended in the shower area itself.

2.3 Structural Assessment for Sunken Floors

Before committing to a sunken design on an upper floor, establish the joist depth, any services running beneath the floor, and whether joist spans can accommodate trimming for the drain connection. For timber floors, a structural engineer assessment is advisable for excavation deeper than 30mm. For concrete floors, a minimum slab thickness of 100mm is generally required to safely accommodate a 50mm recess.

Section 3: Materials & Drainage — Getting the Foundation Right

3.1 Waterproofing Systems

The waterproofing layer is the single most important component of any wet room. The tiles, the screen, and the drain are all visible and replaceable. The waterproofing is invisible and, if it fails, the consequences reach through the floor and into the structure below.

Non-negotiable details for any system:

• All internal corners (wall-to-wall and wall-to-floor) must be reinforced with fabric tape before liquid membrane is applied , this is the most common location for membrane failure.
• The drain surround requires specific treatment — see Step 4 in Section 5.
• All screws and fixings that penetrate the waterproof layer must be sealed with the specified compound.

3.2 Drainage — Linear Drain vs. Point Drain

Linear Drain — Strongly Recommended

A linear drain is a channel drain that runs along one wall, collecting water across its full length. The floor falls in a single direction toward the channel — the simplest geometry to achieve and verify.

• Single-direction fall: Straightforward to achieve in screed or on a pre-formed former, and easy to verify before tiling begins.
• Works at any size: Equally suited to a 3 m² sunken wet room and a 6 m² open wet room. Drain length matches the shower zone width.
• Clean visual result: A stainless steel channel at the wall base is architecturally minimal and suits both large-format and mosaic tiles.
• Easy to clean: The grating lifts out for access to the channel below.

Point Drain — Limited Applicability

A central point drain requires the floor to be graded toward a single point from four directions. Point drains are not recommended for small bathrooms under 4 m² — the four-direction gradient is significantly more difficult in a small space and routinely produces uneven results. In larger bathrooms of 5 m² or more, a centrally positioned point drain can work, but only if the gradient is verified with a laser level and the work is carried out by an experienced tiler.

3.3 Floor Tile Specification

• Slip resistance: R10 minimum; R11 preferred for fully open wet rooms.
• Tile size and gradient: Smaller tiles (100mm mosaic) accommodate the gradient naturally. Large-format tiles (600mm+) require skilled back-buttering and are not recommended for DIY installations.
• Grout: Flexible, waterproof grout throughout. Rigid grouts crack under thermal cycling in wet room environments.

3.4 Complete Materials Checklist

• Waterproofing: Liquid tanking membrane · Waterproof board (for walls) · Fabric reinforcement tape · Board screws and sealant compound
• Drainage: Linear drain channel with stainless steel grating · 40–50mm waste pipe and fittings · Drain sealant kit
• Floor construction: Pre-formed wet room former (non-sunken DIY) or sand/cement screed mix (sunken) · Flexible waterproof tile adhesive
• Tiling: Floor tiles R10/R11 (allow 10% wastage) · Wall tiles or waterproof panels · Flexible grout · Silicone sealant (all corners and glass interfaces)

Section 4: Choosing Your Shower Screen

4.1 Wet Rooms Don't Have to Be Screenless

There is a persistent misconception that a wet room means a completely open shower space with water spraying freely in all directions. In practice, the vast majority of UK wet room installations and virtually all wet & dry zone configurations include a glass panel or screen of some kind.

The screen serves two functions: it contains water within the shower zone (protecting the dry zone and nearby electrical fittings), and it provides a degree of enclosure that most people find more comfortable. A single fixed glass panel, positioned correctly, achieves both without compromising the open, contemporary aesthetic.

For a complete guide to walk-in shower formats, see: Should You Buy A Walk In Shower? Everything You Need To Know!

4.2 Walk-in Screen vs. Frameless Sliding Door

Walk-in Shower Screen (fixed panel)

A single panel of glass or two panels in an L-configuration fixed to the floor and/or wall without a door. Entry is fully open from the panel's open side. No hinges, no tracks, no door seals. The entry is completely unobstructed.

Walk-in screens work best in shower zones at least 1,200mm wide, which gives sufficient depth for the panel to contain spray without the open side being adjacent to the showerhead.

Frameless Sliding Shower Door

Combines the visual clarity of frameless glass with the water containment of an enclosed space. The better choice for small wet & dry zone installations particularly where the shower zone is 900mm wide or less — because it provides full splash containment without requiring hinged swing clearance.

4.3 Glass Specification

• Thickness: 8mm for panels up to ~1,000mm wide; 10mm for larger walk-in screens.
• Safety standard: Must comply with BS EN 12150 for thermally toughened soda lime silicate safety glass. Confirm compliance before purchasing.
• Easy-clean nano-coating: Causes water to bead and roll off rather than forming mineral deposits. Without coating, hard water limescale accumulates within weeks. Durovin screens include NANO coating as standard.
• Height: 1,850mm minimum; 2,000mm preferred for better spray containment.

Section 5: Step-by-Step Installation Guide

The following sequence applies to a wet & dry zone wet room with a sunken floor and linear drain — the most common and practical configuration for UK bathrooms.

1. 1

    

   Strip Out & Assess

   Remove all existing fittings include bath or shower enclosure, basin, floor tiles, and wall tiles in the wet zone. Expose the subfloor and walls to assess their condition.

   For a sunken installation: Determine the exact position and height of the linear drain based on the planned floor gradient. Mark the extent of excavation. On concrete, use an angle grinder to score the perimeter and a cold chisel or SDS drill to break out to the required depth. On timber, cut back floorboards carefully — seek structural advice before trimming any joist. Check for existing pipework or cables before cutting.

2. 2

    

   Install the Drain

   Position the linear drain channel at the base of the wall, with the top of the grating set 3–5mm below the anticipated finished floor level.

   Critical check before fixing the drain: Verify that the planned floor gradient from the furthest point of the shower zone to the drain channel, it achieves at least 2%. Use a long spirit level and tape measure, or a laser level. If the gradient cannot be achieved at the planned drain height, adjust drain position before fixing permanently.

   Connect the waste pipe to the drainage stack at a gradient of at least 1:40 (25mm per metre of pipe run). This is separate from the floor gradient — both must be correct. Cap the drain opening temporarily to prevent debris entering during installation.

3. 3

    

   Build the Floor

   Sunken floor with screed: Fill the excavated area with a 4:1 sand/cement screed mix, working from the back of the zone toward the drain, building the gradient into the screed surface. Allow to cure fully — at least 24 hours before applying waterproofing.

   Non-sunken with pre-formed former (recommended for DIY): A factory-manufactured panel with the gradient pre-built into its surface geometry. Bond to the subfloor with suitable adhesive — no screed skills required.

   Once the floor is complete, verify the gradient by pouring water at the furthest corner and confirming it flows directly to the drain without pooling.

4. 4

    

   Apply the Waterproofing

   This is the most important step in the entire installation.

   • Surface preparation: Clean, dust-free, structurally sound. Fill all cracks or voids.
   • Corner reinforcement: Bed fabric reinforcement tape into all internal corners using the first coat of membrane as adhesive. Press flat — no air bubbles.
   • First coat: Apply liquid tanking to floor and all wet zone walls at the manufacturer's specified coverage rate. Allow to cure to tack-free (typically 2–4 hours).
   • Second coat: Apply perpendicular to the first coat direction (cross-hatch method).
   • Drain surround (three coats): The drain-to-membrane junction is the most common single point of failure. Use the drain manufacturer's sealing collar or butyl ring. Apply membrane over the collar, not under it.
   • High-risk areas: Apply a third coat at all corners, along the base of all walls, and around the drain surround.
   • Cure time: Do not tile until the membrane has cured for a minimum of 24 hours. Allow longer in cold or humid conditions.
5. 5

    

   Wall Preparation

   If using waterproof board on walls, fix boards using manufacturer-specified fixings. Apply specified joint tape and compound to all board joints and corners. All screw holes that penetrate the waterproof layer must be sealed with sealant compound.

   For the sunken floor: ensure the transition between the sunken wet zone and the dry zone floor level is waterproofed at the vertical face and the horizontal lip.

6. 6

    

   Floor and Wall Tiling

   Floor: Begin laying tiles from the wall opposite the linear drain, working toward it. Use flexible polymer-modified tile adhesive throughout — standard cement adhesive does not have sufficient waterproof performance for a wet room floor.

   Walls: Start with the first full row of tiles at the base of the wall. Work upward. Cut tiles go at the top where they are less visible.

   Critical rule for internal corners: Do not grout internal corners — wall-to-wall or wall-to-floor. These joints must be filled with silicone sealant, not grout. Grout is rigid and will crack under thermal movement. Silicone is flexible and maintains the watertight seal.
7. 7

    

   Install the Shower Screen

   Fixed walk-in screen: Position the wall channel or U-profile and mark fixing positions. Pre-drill through tile with a diamond tile bit, then into wall substrate. Insert glass panel and secure per manufacturer's instructions. Apply a continuous bead of clear silicone at the glass-to-tile interface, leaving a 3–5mm expansion gap — this accommodates thermal expansion and prevents stress cracking.

   Frameless sliding door: Fix the top channel first (perfectly level), then the bottom guide track. Hang door panels, adjust rollers. Apply silicone to all fixed glass-to-tile interfaces.

   In both cases: use a spirit level to confirm the glass is vertical before the silicone cures. A misaligned panel cannot be corrected once the sealant has set without removing it entirely.

   For sizing guidance: Should You Buy A Walk In Shower? Everything You Need To Know!

8. 8

    

   Install Fittings

   • Showerhead and valve: Wall-mounted is the simpler installation. Confirm valve position in relation to the screen — the showerhead should direct water toward the drain, not toward the open entry.
   • Grab rails: Must be fixed through the tile and waterproof layer into the wall substrate (not just into the tile). All fixing holes must be sealed with waterproof sealant around the rail base plate before and after fixing.
   • Extractor fan: Any new electrical connections must be carried out by a Part P-registered electrician.
9. 9

   Final Seal & Water Test

   Block the linear drain outlet with a rubber bung. Fill the shower zone floor with water to approximately 50mm depth. Leave for 24 hours. Inspect the ceiling and walls of the room below — any visible moisture indicates a waterproofing failure that must be located and remedied before the bathroom is used.

   Check all silicone joints: no air bubbles, no gaps, no areas where sealant has not adhered. Rectify any deficiencies before use. Remove the drain bung once the test has passed.

Section 6: Wet Room Cost Guide UK (2026)

Where to invest the budget: Waterproofing and drainage account for a disproportionate share of long-term performance. Spending on a quality tanking system and a well-specified linear drain — rather than premium tiles — is the better allocation when the budget is constrained.

Section 7: Common Mistakes & How to Avoid Them

1. Floor gradient below 2%. Measure before and after screed application, and verify again before tiling. A 2% gradient over a 900mm run is only 18mm of fall — easy to under-achieve without careful measurement.
2. Using a point drain in a small bathroom. Four-direction gradients converging on a single central point in a compact space routinely produce uneven results. Use a linear drain.
3. Unsealed drain surround. The junction between the drain body and the liquid membrane is the single most common waterproofing failure point. Use the drain manufacturer's sealing collar and apply membrane over it — not just around it.
4. Grouting internal corners. Rigid grout in a corner joint will crack within months due to thermal movement. All internal corners in a wet room must be filled with flexible silicone sealant.
5. Installing the glass screen without an expansion gap. Glass expands with temperature. A screen sealed hard against tile at the base and side will develop stress cracks or dislodge the sealant within a year. Always leave 3–5mm and fill with silicone.
6. Insufficient ventilation. A wet room generates more airborne moisture than a standard shower enclosure. Specify a humidity-sensing fan with an extract rate above the Part F minimum.
7. Skipping structural assessment for upper floor sunken installation. Joist damage, settlement, and long-term deflection will change the floor gradient over time — creating drainage problems and potential structural issues. Always assess before excavating.

Section 8: Maintenance & Longevity

Wet Room Build Checklist

Work through this checklist from planning to completion. Items are saved for this session.

Frequently Asked Questions