Introduction

Ever priced a wetroom that looked straightforward, then lost a day fighting falls, a shallow waste, or a fan that was never going to meet extraction? It’s common. A wetroom succeeds or fails at survey. In this guide, I’ll walk you through a practical, step-by-step process to check falls, drainage, substrates, services, and thresholds so you don’t inherit hidden risks. You’ll see what to measure, what to photograph, where projects go wrong, and how to turn a clean survey into a clean proposal—fast.

Table of Contents

• Key Takeaways
• Start With Constraints And Client Use
• Drainage, Falls, And Waste Feasibility
• Substrate And Waterproofing Readiness
• Services: Water, Heat, Ventilation, Electrics
• Thresholds, Doors, And Finishes That Last
• Frequently Asked Questions
• Conclusion

Key Takeaways

• Many contractors find a thorough wetroom survey saves 2–3 site revisits and 1–2 hours of admin per job.
• Industry guidance commonly targets floor falls of roughly 10–15 mm per metre in the wet area for reliable drainage.
• In the UK, Building Regulations guidance for bathrooms generally expects intermittent extract fans around 15 l/s; plan wiring and duct runs early.
• For shower wastes, a typical pipe gradient of about 1:40 to 1:80 helps prevent standing water and blockages.
• Contractors often report that capturing survey notes by voice with photos reduces back-and-forth with clients by half.

Start With Constraints And Client Use

Wetrooms fail when assumptions are fuzzy. The problem is scope: unclear user needs, missed structural constraints, and fixtures chosen after the fact.

What To Clarify First

• Users and accessibility: wheelchair turning, bench, grab rails, threshold-free entry.
• Shower performance: expected flow rate. Many modern showers deliver around 10–14 l/min; that drives waste sizing and fall quality.
• Finished floor build-up: underfloor heating, decoupling, tile thickness, levelling compounds.
• Adjacent rooms: ceiling below, neighbours, or heritage constraints that affect drilling or pipe routes.

Quick Survey Method

1. Walk the room and mark potential shower zone on the floor.
2. Measure existing floor level variance with a laser; note high/low points.
3. Photograph corners, joist directions (if known), and existing wastes/soil stack routes.
4. Voice-capture the brief (who uses it, desired fixtures, heating preference, finishes).

Real-World Example

A first-floor timber bathroom with a client wanting a 300 mm overhead drencher and a linear drain at the far wall. Early check shows joists run parallel to the desired waste route, with a steel at mid-span. Solution: relocate drain nearer the stack, switch to a centre waste former, and specify a compatible trap height. Clear at survey, no surprises later.

Drainage, Falls, And Waste Feasibility

Most callbacks come from slow drainage or odours. The root cause is usually inadequate falls, a shallow trap, or long flat waste runs.

The Problem

• Insufficient fall across the wet zone.
• Long runs with minimal gradient to the stack.
• Trap too shallow for the chosen flow rate.

The Solution

• Target falls around 10–15 mm per metre towards the drain in the wet area. This balances drainage and comfort.
• Plan gradients: a typical waste fall of about 1:40 to 1:80 is commonly used in bathrooms; tighter spaces push you to the steeper end.
• Choose a trap with a reliable water seal. Many wetrooms use a 50 mm water seal trap to resist odours, especially with higher-flow showers.
• Keep runs as short and straight as possible; minimise horizontal offsets.

Checks To Perform

• Laser level the proposed shower area; note available build-up and where you’ll create falls.
• Confirm waste route to stack or external soil—measure distance and elevation changes.
• Verify trap height vs structural depth (joists or slab recess).

Example Layout Choice

• If the floor depth is limited, a centre waste former can reduce pipe length and optimises fall.
• If the client wants a linear drain, align it perpendicular to joists where possible to simplify notching and maintain structure.

Substrate And Waterproofing Readiness

Tiles don’t crack on their own; substrates move. The problem is deflection and moisture pathways.

The Problem

• Timber floors with noticeable bounce or unknown joist condition.
• Cracked screeds or patchy, dusty concrete surfaces.
• Incomplete or poorly overlapped waterproofing.

The Solution

• Timber floors: overboard with suitable wetroom panels or a rigid board, and stiffen from below if accessible. In general, tile manufacturers aim for limited deflection (often referenced around L/360) to protect grout and tile.
• Concrete: repair cracks, prime, and plan falls with levelling and shaping compounds before tanking.
• Tanking: fully tank the shower area—commonly the entire floor plus upstands, and full-height on shower walls. Lap membranes at corners and penetrations. Seal pipe penetrations with collars.

Quick Comparison: Substrate Focus

Real-World Example

Ground-floor concrete bathroom with 6–8 mm dips. Plan: patch repair, primer, create falls with a fibre-reinforced screed to the linear drain, then apply a full tanking system. Result: flat, drained, and sealed base that tiles fast and stays put.

Services: Water, Heat, Ventilation, Electrics

Wetrooms are systems. Miss one service detail and you’re back for rework.

Water And Heating

• Confirm hot and cold routes, isolation points, and expected shower flow (e.g., high-flow drencher vs standard handset).
• Underfloor heating? Account for build-up, sensor placement, and sequencing with tanking and tiling.

Ventilation

• In the UK, guidance under Part F typically expects intermittent bathroom extract around 15 litres per second. Confirm fan location, duct path, and termination early.
• Longer or kinked ducts reduce performance—keep straight, short runs with smooth-bore ducting.

Electrics

• Bathroom electrical zones exist (commonly referred to as zones 0, 1, and 2 in BS 7671). Select fittings and IP ratings accordingly (e.g., IPX4 commonly used in zone 1, with RCD protection).
• RCD protection around 30 mA is generally expected for bathroom circuits; confirm at survey and allow for any consumer unit upgrades.

Example Coordination

Client wants a ceiling rain head, wall handset, LED niche strip, mirror demister, and UFH. Sequence: 1) set manifold and routes; 2) agree fan and duct route to external wall; 3) plan switching (two-gang with fan overrun); 4) UFH mat and probe on top of tanking where the system requires, or below per manufacturer—document the stack-up clearly.

Thresholds, Doors, And Finishes That Last

Many contractors discover at the end that the bathroom door now scrapes or the hallway can’t handle a flush transition. Plan it now.

The Problem

• Build-up increases finished floor height at the doorway.
• Water escaping beyond the wet zone without a subtle containment detail.

The Solution

• Model the build-up: substrate prep, falls, tanking, UFH, adhesive, and tile. Check door clearance and adjacent floor levels.
• Use subtle containment: tile-in strip, slight ramp at the perimeter, or layout the falls to keep splash water heading to the drain.
• Choose slip-resistant tile in the wet area. It’s common to select a higher grip finish underfoot while keeping matching wall tiles smoother.

Practical Doorway Check

• Measure door undercut available vs planned floor increase.
• If trimming the door, confirm fire-door status (where applicable) and client approval.
• Photograph the threshold area and voice-note the agreed solution.

Frequently Asked Questions

Can I Build A Wetroom On A Timber Floor?

Yes, but only with proper stiffening and overboarding. Check joist direction, span, and condition. Overboard with wetroom-rated panels, plan your drain so the trap sits within available depth, and fully tank the area. Many contractors find that a centre waste former on timber simplifies falls and pipe runs.

What Floor Fall Should I Aim For?

In general, around 10–15 mm per metre towards the drain in the wet zone works well. Steeper falls drain faster but can feel sloped underfoot. Balance comfort with drainage, and ensure the entire wet area pitches to the waste with no backfalls.

What Ventilation Is Needed In The UK?

Commonly, intermittent bathroom extract around 15 l/s is used, with suitable siting and ducting per guidance in Part F. Keep duct runs short and straight to maintain performance, and confirm an external termination is achievable without awkward bends.

Do I Need A Special Trap Or Waste Size?

For higher-flow showers, a deep-seal trap (commonly 50 mm water seal) with a clear route to the stack is a solid choice. A typical pipe gradient of about 1:40 to 1:80 is used to move water effectively and minimise blockages. Match the trap and grate capacity to the shower’s flow rate.

Where Should The Waterproofing Go?

Fully tank the floor and upstands, and go full height on shower walls. Seal corners and penetrations with compatible tapes and collars. This approach significantly reduces moisture ingress risks and is standard practice for durable wetrooms.

Conclusion

A wetroom that drains, ventilates, and lasts starts with a disciplined survey. Confirm user needs, map drainage and falls, stabilise the substrate, coordinate services, and plan thresholds. Capture everything—dimensions, photos, voice notes—while you’re there. Then turn it into a clean, signable offer.

If you want to cut the admin, use Donizo. Speak your findings onsite with voice, add photos, and generate a professional proposal fast. Send a branded PDF, get a legally binding e‑signature, and when the client accepts, convert it to an invoice in one click. Contractors often report saving 1–2 hours per job and avoiding the usual back-and-forth. That’s time back on the tools—and a wetroom that goes right first time.