The main rule
A change during the works is only carried out after three steps: you describe what changes; the contractor assesses price, time and affected work; you confirm in writing. Anything done outside that chain turns into a dispute at final account.
Changing your mind during a renovation is normal. Problems start when the change exists only as a voice note to the foreman and the crew does it "the way they understood it".
When a change is cheap and when it is expensive
The cost of a change depends on the stage the job is at. Before first fix, moving a socket is a correction on the drawing. Once the cable is run, it is a new chase and new cable. Once the wall is plastered and painted, it is a chase, filling, skimming and repainting the whole wall.
Plumbing works the same way: moving a basin before the screed costs almost nothing; once tiled, it means lifting tiles, a new drainage run and new tiles, which you also have to find from the same batch.
The practical conclusion: the more decisions are made before strip-out, the fewer expensive changes later. The kitchen, bathrooms and electrics are best signed off completely before first fix starts.
How to describe the change
Describe the previous decision and the new one: which product, where, how many, what finish. Attach the product reference, a photo or a mark on the plan. "Do it as we discussed" will not do: in two weeks nobody will remember exactly what was discussed.
Keep questions separate from decisions. "How much would it cost to move the door?" is a question, and the crew should not start work on the strength of it. If you are still comparing options, say so plainly: "do not proceed yet".
What the assessment should show
A good assessment of a change answers five questions. What the change itself costs. Which completed work has to be redone or thrown away. Which ordered materials cannot be returned: bespoke furniture and made-to-measure doors and glass usually cannot. How much time it adds and whether that pushes other work back. Whether the change alters the permit regime: moving a partition can take the job outside what was notified to the council.
A cheaper material does not always make the renovation cheaper. Swapping a tile for one of different thickness changes the floor level, thresholds and doors. Ask for a comparison across every affected item, not just the price of the material.
An example: one door on a job with concealed doors
At the 250 m² child psychology centre in Eixample, which we built between January and June 2026, there were 24 concealed doors flush with the walls. On a job like that, moving one door half a metre after its concealed frame is fitted would mean a new frame, rebuilding the partition, re-skimming and repainting the wall, moving the switch and possibly changing the lighting scene.
A change like that is entirely possible. But the client should see the full chain of work and the cost before the crew picks up the grinder, not on the final invoice.
When the contractor proposes the change
Changes also come from the other side. The strip-out reveals a rotten beam or a pipe that cannot stay, or the chosen material has been discontinued. The procedure is the same: the contractor shows the problem on site or in photos, proposes a solution with price and time, and you confirm in writing before it is carried out.
Swapping a material for an "equivalent" without your agreement is not a site detail but a breach of what was agreed, even if the equivalent is no worse. How to assess such a substitution and when a price increase is justified are covered in separate articles.
One approved version
An accepted change is recorded with its date and a reference to the updated quote or drawing. At the same time you decide who tells the crew and suppliers: if the foreman knows but the joiner making the wardrobe does not, a mistake is guaranteed. Rejected options are recorded too, so they do not circulate on site as if approved.
At handover, changes are checked separately against their own list and included in the final account.
On our projects one person runs the job and every change goes through them: assessment before work, written approval, instruction to the crew. Staged payments under the contract, in Russian or Spanish. We reply to enquiries within an hour.