What Additional Costs Should I Expect When Replacing Windows?

The quote for your new windows covers the windows themselves and their installation. But it doesn’t always cover everything else that comes with the job. Some additional costs are predictable, some only emerge when old windows come out and reveal what’s behind them.

Often, there are no additional costs arise on top of our quote, but for period properties, bay windows, or jobs requiring structural work, unexpected costs can add up. Here’s what to budget for.

Scaffolding

Most ground-floor and many first-floor windows can be fitted from inside or from ladders. But if you need scaffolding for upper floors, expect to pay £350-650 per elevation for a 2-4 week hire. A three-sided scaffold on a semi-detached can run to £800-1,100 per week. If scaffolding sits on a public pavement, you’ll also need a licence from the council (£100-350).

Ask your installer upfront whether scaffolding is included in their quote or charged separately.

Making Good: Plastering and Decoration

Removing old windows often damages plaster around the reveals (the sides and top of the window opening). Your installer will make basic repairs and, for UPVC windows, will add slim UPVC panels to cover any gaps round the edge of the windows, but a professional plaster finish typically costs £30-60 per window, rising to £50-200 where reveals are badly damaged.

Window Boards and Cills

Internal window boards (sills) sometimes need replacing, particularly if the new window is a different depth to the old one. Internal uPVC cover-boards cost £10-65 supply; timber or MDF boards £30-80 plus £40-75 fitting. External cills typically cost £100-150 supply and fit.

Structural Work

If you’re changing window sizes, converting a window to a door, or if removing old windows reveals a failed lintel, structural work adds significant cost. A concrete lintel replacement runs £650-1,000. A steel beam for a bifold or large opening costs £400-2,100 including labour. A structural engineer’s inspection adds £200-500.

Bay windows deserve special mention. Bay windows often rely on the old frame for structural support. Removing them may require temporary propping and a structural assessment before new windows go in. Budget £800-2,000+ for bay structural work. Always ask your installer for advice.

Waste Disposal

Most reputable installers (such as Cliffside) include disposal of old windows in their quote, but confirm this. If it’s not included, skip hire for a typical whole-house job runs £150-350.

Building Regulations and Certification

Using a FENSA-registered installer, the certification cost is absorbed into the quote – typically around £60. If you use a non-registered installer, you’ll need to apply for Building Control approval separately, costing £150-400+. Read our guide on FENSA certificates for more on why this matters.

Listed Building and Planning Costs

Listed Building Consent applications are free in England, but preparing one is not. You’ll typically need a heritage statement (£300-800), architect drawings (£400-1,500), and possibly specialist joinery surveys. Total preparation costs: £500-2,500.

Other Costs to Consider

Security alarm sensors: Window-mounted sensors may need repositioning after installation.

Blinds and curtains: New windows may be slightly different dimensions, meaning existing blinds or curtain poles don’t fit. Budget for replacements where needed.

Trickle vents: Required by Building Regulations since June 2022. Most quotes include these, but some older quotes may not. Expect £30-100 per window if charged separately.

How to Avoid Surprises

The best way to avoid unexpected costs is to use an installer who conducts a thorough pre-installation survey. During this visit, they should identify potential issues – failed lintels, rotten sub-frames, structural concerns with bays – before you commit.

Ask specifically what’s included in the quote and what isn’t. A detailed written quote should itemise everything: products, installation, disposal, FENSA certification, making good, and any excluded items.

We always aim to identify potential additional costs during our initial survey so there are no surprises on installation day. Contact us for a detailed, transparent quote.

Frequently Asked Questions

Should I budget a contingency?

Yes. We recommend 10-15% of the window quote as a contingency for unexpected repairs, particularly on older properties where you don’t know what’s behind the existing frames until they come out.

Can I do the making good and decoration myself?

Absolutely. Many homeowners handle internal decoration themselves to save money. Just wait 24-48 hours for sealants to cure before painting around new windows.

Is VAT included in window quotes?

Replacement windows are standard-rated at 20% VAT. This should always be included in the quoted price. Be wary of any quote that excludes VAT.