Sash windows Cost Calculator

How this calculator works

Every figure in this calculator is the one published in the cost table on our sash windows guide. Pick the option that matches your job and the calculator returns that published range, adjusted for your region - it does not model anything the guide does not already say.

That is deliberate. A calculator whose rates drift from the page it sits under is worse than no calculator, because two numbers on the same site disagree.

What it cannot know: access, the condition of what is already there, and anything structural. Those are what separate three real quotes from each other.

What actually moves a sash window quote

The calculator hands you a fair budget figure, but two joiners standing in the same bay can still quote a good way apart. It’s usually down to things a dropdown never sees – the state of the timber, how the window is balanced, and whether you’re keeping the original box or tearing it out.

Repair or replace. This is the big fork, and it swings the price more than anything else on the page. A sound box frame with a bit of rot in the sills and rails can be repaired and re-corded for far less than a full replacement. Once the frame itself is soft or the joints have opened up, patching stops being economical and a new window earns its keep. A good quote will say which camp your windows fall into, not just price the job you asked for.

Timber, uPVC or slimline double glazing. Softwood is the baseline most of these figures assume. Hardwood costs more but lasts longer and takes paint better. uPVC sash is cheaper again, though the sightlines are chunkier and it rarely suits a period frontage. If you want to keep single-glazed originals but lose the draughts and noise, slim-profile or vacuum double glazing retrofitted into the existing sashes sits in the middle – more than a refurb, less than a full replacement.

Weights, cords and how it’s balanced. A traditional box sash runs on lead or iron weights hung on cords over pulleys, hidden inside the frame. Re-balancing that properly means opening the box, replacing the cords and often the pulleys, and matching the weights to the new glass – heavier double glazing needs heavier weights or the sash won’t stay put. Cheaper replacements swap the whole cords-and-weights system for spring balances, which is quicker to fit but changes how the window feels and isn’t what a conservation officer wants to see.

Draught-proofing that’s worth having. The version that lasts routes brush seals into the staff and parting beads while the sashes are out, so the window still slides but stops rattling and leaking. It’s slower than tacking on stick-on strips, and that labour shows up in the quote. Ask what’s actually being sealed before you set two numbers side by side.

Consent, if the house is protected. In a conservation area or on a listed building you can’t always swap the windows for whatever you fancy – the material, the glazing bars and even the depth of the double glazing may be dictated for you, and listed buildings need consent before work starts. Check with your council or the Planning Portal windows guidance first, because a quote priced on standard replacements can change completely once heritage rules apply.