Exposed: 10 Hidden Bathroom Costs Only Builders Know!
Why Your Bathroom Renovation in London Might Cost More Than You Think
You’ve decided to upgrade your bathroom. It’s exciting! Sleek tiles, shiny taps, a brand-new tub. You talk to a few bathroom builders in London, check out some designs, and make a budget. But here’s the twist: that budget might not cover everything.
According to a 2024 survey by Rated People, 61% of UK homeowners reported going over budget during renovations — and bathrooms are one of the most common areas. The reason? Most people don’t know about the hidden costs builders deal with behind the scenes.
This blog reveals the 10 hidden bathroom renovation costs in London that only seasoned builders truly understand. Let’s dive in — and help you stay ahead of the surprises.
1. Old Plumbing That Needs Replacing
Many bathrooms in London homes are decades old. So, when your builder starts working, they may find corroded pipes, outdated lead piping, or dodgy DIY jobs from past owners.
- Cost impact: Replacing old plumbing can add £800–£2,000 to your budget depending on size and pipe condition (Checkatrade, 2024).
- Why it’s hidden: You can’t see inside the walls or under the floor until the job begins.
Tip: Ask your bathroom builders in London to inspect the pipework before quoting. At CG Bathrooms Limited, expert inspections often save customers from costly surprises down the line.
2. Waterproofing and Tanking
Waterproofing is vital. Skipping it can cause leaks, mold, or even structural damage. But good waterproofing is not always included in basic renovation quotes.
- Cost impact: Professional tanking adds £400–£900.
- Why it’s hidden: It’s not a visible part of the finish, so clients often don’t ask about it.
Tip: Always get waterproofing included in your quote. Professional builders automatically include tanking in wet areas because prevention is cheaper than repair.
3. Electrical Upgrades
Modern bathrooms often need more power: electric showers, underfloor heating, LED mirrors, extractor fans. But older wiring may not handle it.
- Cost impact: Upgrading the electrical system may cost an extra £500–£1,500.
- Why it’s hidden: You don’t realise you need it until an electrician checks the wiring.
According to NICEIC, over 55% of UK homes built before 1980 need rewiring in wet zones like bathrooms.
4. Hidden Water Damage or Rot
Once tiles come off or floors are lifted, builders may find water damage, rotten floorboards, or even black mold.
- Cost impact: Repairs can cost £600–£2,500 depending on severity.
- Why it’s hidden: Damage is usually hidden beneath fixtures or inside walls.
Tip: Ask your builder if they offer moisture checks before starting. CG Bathrooms Limited uses thermal imaging to check for hidden leaks — a big help before stripping out the space.
5. Structural Changes
Want to move your shower to a new spot? Swap your tub for a walk-in wet room? It might mean cutting joists, adjusting beams, or reinforcing walls.
- Cost impact: Structural changes can run £1,000–£3,000+.
- Why it’s hidden: You don’t realise the change impacts the building structure until work begins.
Always consult experienced bathroom renovation experts in London to spot structural limits early.
6. Tile Waste and Pattern Matching
Fancy tiles with patterns or cuts? You may need more tiles than you think — sometimes 10–20% extra — to account for breakage and alignment.
- Cost impact: Buying extra tiles can add £200–£600 to your project.
- Why it’s hidden: Quotes often only cover basic tile cost, not waste or specialty layouts.
Tip: Go over tile layouts with your installer in advance. Ask how much waste is expected, especially for patterned designs.
7. Fixtures That Don’t Fit
You buy a lovely new vanity unit online… only to find it doesn’t fit the existing pipe layout. Now you’re paying a plumber to shift pipes or return the product.
- Cost impact: Rework or customisation adds £300–£800.
- Why it’s hidden: Online orders don’t always match real-world layouts.
Tip: Before purchasing anything, confirm with your bathroom builders in London. CG Bathrooms Limited often guides clients through selections that actually fit — not just look good.
8. Permit and Building Control Fees
In certain London boroughs, especially with older properties or flats, you may need council approvals for plumbing or structural works.
- Cost impact: Building control fees can be £150–£800.
- Why it’s hidden: Many people assume they don’t need permission for internal renovations.
Check your local authority’s website or ask your builder if approvals apply.
9. Unseen Asbestos in Older Homes
If your home was built before the year 2000, there’s a risk of asbestos in floor tiles, artex ceilings, or old backing boards.
- Cost impact: Asbestos testing costs £100–£300; removal ranges £1,000–£2,500.
- Why it’s hidden: It’s not visible, and builders must stop work if asbestos is discovered.
HSE (Health and Safety Executive) reports over 5,000 UK asbestos-related deaths per year — so it’s not worth the risk.
10. Disruption Costs: Hotel Stays & Toileting
If your home has only one bathroom, renovating it may mean you can’t use the toilet or shower for days. That could mean a hotel stay, renting a portable loo, or using a neighbour’s facilities.
- Cost impact: Hotels or alternative toilet facilities can cost £300–£800.
- Why it’s hidden: Many don’t factor in personal inconvenience or temporary arrangements.
Tip: Ask your builder if temporary toilet solutions are offered or included.
Hidden Costs Add Up Fast
Here’s a breakdown based on common findings in London bathroom renovations:
Hidden Cost | Estimated Range |
Plumbing Upgrades | £800–£2,000 |
Waterproofing | £400–£900 |
Electrical Upgrades | £500–£1,500 |
Water Damage Repairs | £600–£2,500 |
Structural Changes | £1,000–£3,000+ |
Tile Waste | £200–£600 |
Fixture Rework | £300–£800 |
Building Permissions | £150–£800 |
Asbestos Testing & Removal | £1,100–£2,800 |
Temporary Living Arrangements | £300–£800 |
A “simple” £8,000 bathroom renovation in London could unexpectedly climb to £12,000 or more if these hidden costs aren’t managed properly.
How to Avoid These Surprises
Want to make sure your bathroom renovation in London goes smoothly and stays on budget? Follow these smart steps:
Get a Full Site Survey
Always start with a survey by professional bathroom builders in London who can identify possible issues early.
Don’t Chase the Cheapest Quote
Low quotes often skip essentials like waterproofing or quality fixtures. Choose a builder who offers itemised, transparent estimates.
Check for Experience
Work with a company like CG Bathrooms Limited, who’ve helped hundreds of London homeowners upgrade their bathrooms without blowing their budget. Their experience means they spot hidden issues before they become problems.
Plan for Contingencies
Set aside at least 10–15% extra budget for unknowns. That way, if something comes up, it’s not a disaster.
Avoid DIY Where It Matters
YouTube is great for painting tips — not for plumbing or electrics. Improper installations can cost more later.
Final Thoughts: The Real Cost of "Cheap"
A bathroom renovation isn’t just about beautiful finishes — it’s about what lies beneath. Hidden costs can wreck your budget and delay your project.
By staying informed and working with seasoned bathroom builders in London like CG Bathrooms Limited, you can avoid most of these pitfalls and enjoy a smooth, stress-free renovation.
So next time you hear “It’s just a bathroom,” remember: even the smallest rooms hold the biggest surprises.