Summary

Bath replacement is one of the most common bathroom jobs on a plumber's diary. The work itself is simple in theory — disconnect waste, disconnect taps, lift out, lift in, reconnect — but in practice the job is dominated by the second-order tasks: tile damage at the bath edge, silicone-trapped flanges, plasterboard rot behind a panel, joist notching where a heavier bath is installed, and the inevitable discovery that the old waste run is at the wrong fall.

The biggest pricing mistakes are: quoting on a like-for-like assumption when the new bath has different dimensions (forcing a re-tile), forgetting that steel and cast iron baths add a structural loading consideration, underpricing the waste pipework where access is tight, and failing to allow time for silicone removal and replacement around the new bath edge. Most "1-day swaps" become 1.5-day jobs once the old silicone is cut out and the tile edge is found to be chipped.

This guide covers four scenarios: like-for-like acrylic swap, upgrade to steel or cast iron, freestanding bath install, and bath-to-shower conversion. For full bathroom refurbishment costs see related articles on tiling and plumbing.

Key Facts

Quick Reference Table

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Scenario Labour Days Material Cost Total Cost (Regional) Total Cost (London)
Like-for-like acrylic swap (same footprint) 1-1.5 £250-£500 £650-£1,450 £900-£1,750
Acrylic to steel enamel upgrade 1.5-2 £450-£1,100 £1,200-£2,200 £1,500-£2,600
Acrylic to cast iron (freestanding) 2-3 £900-£2,800 £2,200-£5,200 £2,800-£6,200
Freestanding bath install (new waste run) 2-3 £900-£3,200 £2,800-£6,500 £3,500-£7,800
Bath swap + full surround re-tile 2.5-4 £450-£1,200 £1,400-£3,200 £1,800-£3,900
Bath to walk-in shower conversion 2-4 £600-£1,600 £1,800-£4,200 £2,400-£5,200

Detailed Guidance

Like-for-Like Acrylic Swap

The bread-and-butter job. Old acrylic bath comes out, new one goes in, same footprint, same taps position, same waste position. Achievable in 1 day if everything aligns; 1.5 days if any tile or silicone repair is needed.

Day 1 sequence:

  1. Isolate hot and cold supplies (typically under-sink or local stopcock)
  2. Disconnect taps (allow corroded back-nuts — penetrating spray, basin spanner)
  3. Disconnect bath waste and overflow
  4. Cut existing silicone bead between bath and tiles (carbide blade or silicone remover)
  5. Remove bath panel
  6. Lift bath out (acrylic baths are 12-20kg; one person)
  7. Inspect framing, joists, and pipework
  8. Fit new bath cradle / feet (per manufacturer template)
  9. Position new bath, level both ways, screw cradle to floor
  10. Connect waste (40mm trap, P or S to existing run)
  11. Connect taps and check seals
  12. Fill bath ¼ full to check for leaks before sealing
  13. Apply silicone bead (low-modulus sanitary silicone, 6-8mm bead)
  14. Refit panel
  15. Customer handover

Pricing example (regional, mid-range acrylic):

Item Cost
Carron Phoenix 1700×700 acrylic bath £210
Bath cradle, feet, fixings £45
Pop-up waste and overflow chrome £55
Bath/shower mixer tap £160
Acrylic front panel £55
40mm waste trap and connectors £25
Low-modulus sanitary silicone × 2 £12
Plumber 1 day £340
Apprentice 0.5 day £120
Disposal of old bath £30
Margin 22% £246
Total £1,298

This is the "competitive but profitable" mid-pricing. Cut below this and warranty and remedial cost will eat the margin.

Upgrading to a Steel Enamel or Cast Iron Bath

Steel enamel baths (Kaldewei, Bette) are heavier (25-45kg) but still installable by one person. The enamel surface is harder-wearing than acrylic and resists scratching and chemical attack — popular with customers spending £1,200-£2,000+ on the bath alone. Pricing premium is mostly material; labour is similar to acrylic with an extra 1-2 hours for the lift and level.

Cast iron is a different proposition. A 1700mm reproduction cast iron bath weighs 80-150kg empty and 250-400kg full. The job requires:

Pricing example (regional, mid-range cast iron freestanding):

Item Cost
Reproduction cast iron 1700mm freestanding bath £1,250
Freestanding bath shower mixer with riser £380
Pop-up waste with stand pipe £85
Floor reinforcement (timber + fixings) £80
Plumber 2 days £680
Apprentice 1 day £240
Carpenter ½ day £180
Disposal of old bath £60
Margin 22% £661
Total £3,616

Freestanding Bath Install — The Waste is the Job

A like-for-like swap reuses the existing waste run. A freestanding bath usually doesn't — the waste comes through the floor in the middle of the bathroom rather than at the end wall. This means either:

Falls matter. The waste needs a minimum 18mm/m (approximately 1:55) fall as per BS EN 12056-2. Where the bath is on a second floor and the soil stack is on the opposite side of the room, this can mean dropping into a void, running 4-6m of 40mm pipe, and adding additional waste fittings.

Building Regulations Part H covers drainage and waste disposal. The waste must discharge to a vented soil pipe, an air admittance valve (BS EN 12380), or an external gully with a trap seal.

Bath-to-Shower Conversion

A common upgrade for older customers or in low-use bathrooms. Rather than refitting a bath, the bath is removed and a walk-in shower tray or wet room installed. Considerations:

Conversion typically runs 2-4 days and £1,800-£4,200 regional. Customers often underestimate the tiling cost — a full walk-in shower zone re-tile is 6-12m² of tiling at £60-£90/m² supplied and fitted.

Tile and Silicone Edge — Where Most Disputes Start

The largest variable in a bath swap is the tile interface. If the new bath sits at exactly the same height and the same overhang as the old bath, the silicone bead can be cut, the bath replaced, and a new bead applied. Most jobs are not this clean. Common scenarios:

Allow 1-2 hours of contingency in every bath swap quote for silicone and tile remediation. If the existing tiles look ropey, recommend a full surround re-tile in the quote — £450-£900 added cost.

Building Regulations and Water Byelaws

The headline regulations:

For most domestic bath replacements, compliance is straightforward: standard deck-mounted bath taps with the spout terminating above the bath rim provide a Type AB air gap by default. The risk areas are flush-deck taps, bath-fill from below, and any submerged or near-submerged inlet which would create a backflow risk.

Common Pricing Mistakes

Frequently Asked Questions

How long does a bath replacement take?

A straight like-for-like acrylic swap is 1-1.5 days for one plumber. A swap with a full surround re-tile is 2.5-4 days (plumber + tiler). A freestanding bath install with a new waste run is 2-3 days. A cast iron upgrade is 2-3 days. The customer is without the bath for the full duration; if a shower is in the same room they will likely have no bathing facility for 1-3 days.

Do I need Building Regulations approval to swap a bath?

No — a like-for-like bath replacement is exempt from Building Regulations notification. However, the work must still comply with the regulations (Part G for sanitation, Part H for drainage). If the swap involves moving the waste pipe to a different soil stack or significant pipework rerouting, the work may be notifiable. Notifiable plumbing work is covered by competent person schemes such as APHC and the CIPHE.

What's the minimum age for a fitted bath under the regulations?

There is no minimum age, but Building Regulations Part G4 requires that hot water systems serving domestic baths deliver water at no greater than 48°C at the outlet, to prevent scalding. This is achieved with a thermostatic mixing valve (TMV2 or TMV3 rated). Bathrooms in dwellings built or refurbished since April 2010 must comply.

Can I reuse the existing taps?

Usually no. Old taps that have been in service 5-15 years will often have damaged seats, perished washers, or seized headworks. Customers often want to keep "the lovely old taps" — push back. Cost of new mid-range bath taps is £80-£280, which is small relative to the cost of a callback to fix a slow drip 6 months later.

What's the lead time on a freestanding bath?

Standard models 3-10 working days from major suppliers (Victoria Plum, Bathstore, Drench, Soak.com). Specialist solid-surface or copper baths can be 4-8 weeks. Always quote with the lead time on the customer's order before booking the work.

What guarantees apply to a bath installation?

Manufacturer warranties: acrylic baths typically 10-25 years on the shell; steel enamel 25-30 years; cast iron lifetime on the body, 10-20 years on enamel. Installer workmanship warranty is typically 1-2 years on the labour. Tiling around the bath is separately warrantied — most tilers offer 12 months on workmanship.

Regulations & Standards