Specify the bathroom as a working system
Begin with the room dimensions, current layout and the changes that matter to the household. State whether the bath stays, whether the shower is over it or separate, where the WC connects and whether this is the only bathroom. List the items to retain and the items to replace, including small fittings such as wastes, valves, bath panels, mirrors and accessories.
Ask the installer to assess the existing services and substrate before you order products. A new shower’s performance depends on the available hot-water system and supply, while moving the WC can change drainage work. A flush shower entry can involve floor and structural decisions. Describe the access you need and have the design assessed; a photograph of a finished wet room does not specify how to build yours.
What the published cost guides can tell you
The FMB bathroom cost guide quotes individual member estimates, including Passmore’s complete renovation from £12,000 and different figures from London-based Fittra. Checked on 18 October 2026, these are commercial illustrations with different scope and regional context, rather than one measured national average. The cited headline figures do not establish a common VAT basis or quotation date.
That spread is a reason to investigate inclusions. A supply-only suite, a same-layout replacement and a full reconstruction cannot be compared by their headline price. The worked example below is a deliberately defined cost plan. Replace every amount with a site-specific quotation before treating the project as affordable.
Insist on the work behind the tiles
| Work package | Specify and allocate |
|---|---|
| Protection and strip-out | Safe disconnection, removal, disposal and protection of retained areas |
| Substrate | Floor and wall repairs, boards, levelling and support for fittings |
| Wet-area system | Compatible waterproofing, junctions, penetrations and inspection records |
| Services | Pipework, wastes, isolation, heating, electrics and extraction route |
| Finishes and fitting | Tile quantities, trims, grout, sealant, sanitaryware and accessories |
| Handover | Testing, demonstrations, care instructions, certificates and snags |
BAL’s manufacturer guidance explains why tile, adhesive and grout do not by themselves replace suitable waterproofing in a shower or wet room. Ask the installer to identify the complete system and current product instructions. Do not turn a materials allowance into permission to mix incompatible components. Drying and curing periods belong to the specified products and site conditions, not to a universal “ready tomorrow” promise.
Check services and permissions before first fix
Electrical Safety First recommends a registered electrician for bathroom electrical work. Give the electrician the actual shower, lighting, heating and fan specifications. Ask which work is notifiable in England and which test and compliance documents will be provided. A bathroom quote should not silently assume the existing circuit is suitable.
GOV.UK includes bathroom plumbing and electrical alterations among work that can require building-regulations consideration. Confirm the route with the relevant professional or building control body; not every like-for-like replacement has the same notification requirement. Before disturbing suspect old boards, coatings or flooring, have the contractor address asbestos risk. HSE distinguishes contractors’ duties from the position of an owner-occupier; do not assume a general property survey has cleared every material for intrusive refurbishment.
A full bathroom funding example
| Item | Amount |
|---|---|
| Protection, strip-out and disposal | 1,000 |
| Floor and wall preparation | 1,500 |
| Plumbing, wastes and heating labour/materials | 1,800 |
| Electrical work and extraction | 800 |
| Sanitaryware, shower, brassware and accessories supply | 2,600 |
| Waterproofing and tiling materials | 1,400 |
| Tiling, fitting, sealing, decoration and completion labour | 1,900 |
| Construction excluding VAT | 11,000 |
| VAT at 20% | 2,200 |
| Construction including VAT | 13,200 |
| Defined pre-work assessment, final amount | 400 |
| Building-control allowance if applicable, final amount | 300 |
| Temporary washing arrangements and logistics | 600 |
| Chosen reserve: 15% of gross construction | 1,980 |
| Full example funding | 16,480 |
HMRC’s ordinary standard rate supplies the tax assumption, not a claim that every bathroom transaction has identical treatment. Installation labour is allocated to the plumbing/electrical rows or the final fitting row according to trade: the final fitting row excludes pipework and electrical connections already counted. Check the builder’s own breakdown for the same boundary.
Measure tile coverage, then order by product and pack
For a teaching quantity check, assume a rectangular room with a 2.4 m wall height, a 0.8 m × 2 m door and a 1 m × 0.6 m window. Wall area is 2 × (2 + 2.5) × 2.4 = 21.6 m². Deducting the two openings gives 19.4 m². Adding the full 5 m² floor gives 24.4 m² before cuts. This simplified measurement assumes full-height tiling and does not add reveals, niches or extra boxing.
If one suitable tile is specified for both walls and floor, a chosen 10% cutting allowance gives 26.84 m². At 1.44 m² per pack, 19 packs provide 27.36 m². The allowance is an editorial assumption, not a standard minimum; layout and breakage can change it. When wall and floor products differ, round each product separately and check the actual pack coverage. Confirm the tiler’s quantity before ordering non-returnable stock.
Agree a sequence that exposes problems before concealment
- Survey, agree the layout and confirm product compatibility and delivery.
- Protect the route and arrange temporary facilities before strip-out.
- Inspect exposed structure and services; agree any additional scope before proceeding.
- Complete first-fix work and required inspections before closing walls or floors.
- Prepare substrates and install the specified waterproofing system, observing its conditions.
- Tile, fit sanitaryware and complete connections, sealing and decoration.
- Test the finished installation, demonstrate controls and record outstanding items.
Photographs before finishes help record what was installed, but they do not replace testing or a competent assessment. If deterioration appears, ask for a diagnosis and priced remedy. Do not hide a known repair in a vague contingency line or pay for decoration that will have to be removed again.
Questions to resolve before accepting the quote
- Does the price cover every removal, delivery and waste charge?
- Who confirms hot-water suitability, drainage and the extraction outlet?
- Which waterproofing products and preparation are included?
- Who buys the fittings, checks missing parts and bears return costs?
- Which assumptions remain provisional, including the condition below the floor?
- When can the room be used, and which documents and demonstrations come at handover?
Separate product upgrades from essential remedial work. If a £600 gross screen allowance becomes £780, record the £180 difference, rather than adding another £780 to the budget. Keep decisions, purchase records and payments beside the work stages in Reno Pro. The useful result is a bathroom that functions within a complete funding plan, with clear responsibility for each interface.
Sources, date and jurisdiction
- FMB — Bathroom renovation costs: a cost breakdown
- BAL Adhesives — Waterproofing wet areas before tiling
- Electrical Safety First — Electrical safety advice for bathrooms
- HMRC / GOV.UK — VAT for builders: houses and flats
- GOV.UK — Building regulations approval: when needed
- HSE — Introduction to asbestos safety
Sources checked on 18 October 2026. Legal, approvals and contractual explanations in this article concern England. Check separately for Scotland, Wales or Northern Ireland. Prices are GBP; worked figures are editorial teaching examples for the stated scope and location, not market averages, contractor quotations or required reserves. Tax assumptions are stated beside each example.