House Renovation Cost: What Actually Drives the Figure

Why there is no honest average

Per-metre figures and online calculators circulate widely, and they share a flaw: a renovation is not a new build on a known plot. The existing house hides its condition until work starts, and two identical-looking semis can differ by tens of thousands of pounds once the floors come up.

The useful question is not “what does a renovation cost” but “what will this renovation cost, and what could change that”. A good builder answers the second question with an itemised quote and a clear list of provisional sums — the items that cannot be fixed until the building is opened up.

The factors that move the number

Scope is the obvious one: decorating a house and gutting it are both called renovation. Beyond scope, the drivers are consistent across projects, and knowing them lets you sanity-check any quote.

Structure comes first. Removing walls, repairing rotten floors or lintels, and dealing with movement all carry engineering and building control costs that decoration does not. Services come next: a full rewire and new heating system are among the largest single line items in any whole-house renovation, and old houses almost always need both.

• Size and scope: refresh, partial renovation or full strip-back
• Structural work: steels, floor repairs, lintels, movement
• Services: rewire, heating, plumbing, and their age
• Damp and fabric repairs, especially in solid-wall houses
• Specification: kitchen, bathroom and finish choices
• Access, parking and whether you live in during the work

The surprises old buildings hide

Every period renovation carries a contingency because every period building hides something. Rotten joist ends where they sit in damp walls, no lintels over original openings, lead pipework, and previous alterations done badly are the usual finds. None of them is unusual and none of them is visible on a viewing.

A contingency of ten to fifteen per cent is the conventional allowance, and it exists to be spent on findings, not absorbed as profit. A quote with no contingency on an old house is not a cheap quote; it is an incomplete one.

Where the money goes, roughly

Without quoting figures, the shape of a whole-house renovation budget is consistent. The structure and fabric — roof repairs, damp work, windows, plastering — typically take the largest share. Services follow. Kitchens and bathrooms are the most expensive rooms per square metre by a wide margin, because they concentrate plumbing, electrics, tiling and fitted furniture into small spaces.

This is why “how much to renovate a bathroom” or “what does a kitchen refit cost” have the same answer as the whole house: it depends on specification. The same room can be fitted modestly or expensively, and the choice is yours to make with open eyes.

How to read and compare renovation quotes

Compare quotes line by line, not at the bottom line. An itemised quote separates structure, services, joinery and finishes, lists exclusions and marks provisional sums. Two quotes that differ widely almost always include different things — one may carry the kitchen, the redecoration or the skip hire and the other not.

Ask what happens when something unexpected is found. A clear process — work stops, the finding is photographed and priced, you approve before it proceeds — is worth more than a low number with no process behind it.

• Is the quote itemised, and what does it exclude?
• Which items are provisional sums, and why?
• What contingency is allowed, and how are extras approved?
• Are the kitchen and bathroom fit-outs separate scopes?

Phasing the work to match the budget

A renovation does not have to happen at once. Many households phase the work: structure and services first, then the kitchen, then decoration room by room. Phasing costs a little more in total but keeps the project affordable and the house liveable.

The order matters more than the speed. Structure before services, services before plaster, plaster before joinery and decoration. Doing it backwards — decorating before the rewire — is the most expensive mistake in domestic renovation, and it is entirely avoidable.