Most renovation budgets do not fail because of one big mistake. They fail through a series of small, reasonable-sounding decisions. Here is how to keep control from the start.
Almost every renovation client we meet has heard a horror story: a friend of a friend whose kitchen extension ended up costing double. It is worth understanding why that happens, because it is rarely the dramatic failure people imagine.
Budgets fail slowly, not suddenly
In our experience, runaway costs almost never come from a single catastrophic event. They come from twenty small decisions, each defensible on its own, that were never priced against the original budget. Upgrading the tiles. Moving a socket. Adding a rooflight because the room felt darker than expected once the walls were up.
None of those is unreasonable. The problem is that nobody totals them until the final account.
Get the survey done before you get the price
The single biggest driver of renovation overruns is pricing work before anyone has looked properly at what is there. A quotation based on a walk-round and a set of drawings is a guess about the parts of the building nobody can see.
Pay for opening-up works. Lift a floorboard, cut an inspection hole, get a drain survey. It costs a few hundred pounds and it converts the largest unknown in your project into a line on a spreadsheet.
Insist on an itemised quotation
A single figure on a page tells you nothing and gives you nothing to negotiate with. An itemised quotation, broken down by trade and phase, lets you see where the money is, understand what a change actually costs, and compare like with like across contractors.
Be particularly wary of provisional sums. They are legitimate for genuinely unknowable items, but a quotation stacked with them is a quotation that has not been done properly.
Hold a real contingency, and do not spend it early
For a modern property in reasonable condition, hold 10%. For anything Victorian or older, hold 15% to 20%. And treat it as untouchable until the structure is open and you know what you are dealing with. A contingency spent on nicer taps in week three is not a contingency.
Decide the specification before work starts
Changes are cheapest on paper and most expensive on site. A tile changed during design costs nothing. The same change after the substrate is prepared costs labour, materials and programme, and it holds up every trade behind it.
Spend the extra fortnight up front choosing finishes. It is the highest-return time you will invest in the project.
Agree how variations are handled
Before anything starts, agree in writing that no additional work proceeds without a written price and your approval. Any contractor who resists that is telling you something useful.
