In short: when an increase is legitimate
A price change during a renovation is legitimate in four cases: you have changed the scope of work; demolition has uncovered a defect that could not be seen at the survey; under a remeasurement contract, the actual quantities turned out different; or you chose a material dearer than the provisional sum allowed for. In each case the increase is documented in writing before the work is done, with an explanation and a calculation.
Anything else, such as "we forgot to include it", "materials have gone up" with no clause to cover it, or "pay now or we stop", is a reason to pause and get clarity before paying.
The four legitimate reasons
A change of scope at your request. You add a walk-in wardrobe or decide to move the kitchen: that is new work and it is paid for separately.
A hidden defect. A rotten beam under the old floor, a crack in a wall behind the cladding, a lead pipe in the floor slab. There is one condition: a diligent professional could not have seen it at the survey. A difference in measured quantities. If the contract is based on unit rates, the total is calculated on the metres actually installed. A provisional sum. The quote allows €40/m² for tiles and you choose tiles at €90/m²: you pay the difference, and that is fair.
What should never become an extra
Waste removal, primer, protecting the floor and the lift, fixings and grout are part of the work; it cannot be done without them. If a contractor bills them separately after the quote is signed, the quote was incomplete from the start.
The same goes for the foreseeable. Wiring in a 1960s building will almost certainly need replacing, and a professional sees that on the first visit. Rising material prices are not grounds for an increase either, unless the contract has a price review clause. And no increase should arrive as an ultimatum: "pay today or the crew does not turn up tomorrow".
What a properly documented increase looks like
A correct price change is a short document you sign before that work starts. It states what changes and why. It includes photos of the uncovered defect or a description of your request. Quantities are measured and rates are taken from the contract; if the item was not there, the new price is justified. And it says whether the schedule moves.
If the contractor suggests "we'll do it first and price it later", ask for at least a ballpark figure in writing, even in a message. Work done without prior agreement is hard to dispute afterwards, and harder still to pay for with a clear mind.
An example: a hidden defect in an Eixample flat
In many older Eixample buildings the floors rest on timber or steel beams with shallow brick vaults between them. When the floor is lifted, it may turn out that the beam ends next to the facade have rotted after years of damp. Before opening up, neither the contractor nor you can see it. Here the increase is legitimate: a technician has to inspect, strengthening has to be designed and a new item goes into the quote.
Replacing old wiring or soil stacks in the same flat, by contrast, is not a hidden defect: it is visible from day one and belongs in the original quote. Always compare with that question: could a professional have seen it before work began?
How to protect yourself from the contract stage
Ask for a quote with unit rates for each item: then any change in quantities is priced at rates already agreed. Provisional sums should be flagged and have a clear value. In the contract, write down the change procedure: a written proposal, your agreement and only then the work.
Stage payments tied to completed work keep both sides in balance. Before demolition in an old building it makes sense to open up doubtful spots with exploratory cuts, so that some surprises become known items. And keep a contingency above the quote: in older housing stock that is sensible practice, not a sign of mistrust.
How we handle it
We prepare the quote after a site visit and measurements, broken down by item, with levels from €1,000/m² (Basic) up to €3,000/m² and above (Luxury), excluding VAT. Payment follows the contract, in stages. If something new comes up during the works, the person responsible for the project shows it to you on site or in photos, prices it and agrees it with you before it is done.
If you have already been presented with an increase you are unsure about, our article on what to do when a budget spirals explains how to respond. The key point: do not sign or pay under pressure until you have a written explanation.