A renovation cost estimate: how to draw it up and check it

A renovation cost estimate is something many people treat as a formality for the contractor’s bookkeeping rather than a working tool for the client. In reality, the estimate is exactly what determines how much the renovation will cost and where unexpected extra charges will appear along the way. A poorly drawn-up estimate does not save time at the start — it simply pushes every dispute about money down the line, to a point where the cost of a mistake is higher. Below is a breakdown: what an estimate consists of, how to draw it up in the right order, and what to check before signing.

A renovation cost estimate: what it is and why it matters

An estimate is a list of works and materials by item, with the volume and cost of each stated separately. It is not “a rough renovation figure” but a working document you can use to check exactly what is included in the price and what you pay for separately. Without such a list, the conversation with a contractor rests on trust rather than numbers, and any mismatch in expectations surfaces later, on site.

In international project-management practice — whether the Italian Merloni Law or the British RIBA Plan of Work — the estimate appears not at the very start but once the design is ready. The logic is simple: you cannot accurately price something that has not yet been designed. An estimate drawn up by eye before the design exists is always a “give or take” figure, not a working budget.

What an estimate consists of

A proper renovation cost estimate has several mandatory sections:

• demolition works — removing partitions, waste disposal, taking out old plumbing and wiring;
• first-fix works — screed, plastering, electrical and plumbing runs, ventilation;
• finishes — flooring, walls, ceilings, tiling, wallpapering;
• materials — listed separately from labour, with specific items rather than “mid-range materials”;
• fittings and appliances — if their installation and connection fall within the contractor’s scope.

Each section should be broken down item by item rather than collapsed into a single line reading “turnkey renovation”. What that wording actually hides in practice, and why it does not protect the budget on its own, is covered in detail in the article what “turnkey renovation” means.

An itemised estimate, not a single “turnkey” figure

A one-line estimate with a final sum is the main source of conflict on a renovation. If the document does not break down how much demolition costs, how much the screed costs, and how much the tiling costs, the client has no way of knowing where the final figure came from or what happens to it if the scope of works changes.

An itemised estimate solves two problems at once. First, it lets you compare proposals from different contractors on the same figures rather than on general impressions. Second, it becomes the basis for control as work proceeds: any deviation from the scope — smaller or larger — is visible immediately, not discovered only at handover.

The right order: the design first, the estimate second

An estimate is calculated from a finished design, not the other way round. The layout sets the volume of demolition and first-fix works, the electrical scheme sets the number of points and the length of cabling, the interior design sets the list of finishing materials. If the design does not exist yet, the order of the first renovation steps — from layout to choosing a contractor — is covered in the article where to start a home renovation.

The reverse order — looking for a crew and an estimate before the design — almost always ends in a recalculation mid-project: the layout changes, the volumes of work change, and so does the estimate, but by then there is no way to compare proposals on equal terms.

A reserve for unforeseen works

Even a detailed estimate does not remove the need for a reserve. In resale flats, demolition often reveals what could not be seen at the inspection stage: the condition of the screed, the age of the wiring, hidden pipe defects. The reserve is worth setting not “by eye” but as a separate line in the estimate — that way it does not get lost among the other items and does not turn into an unpleasant surprise once the money for the main scope has already been spent.

A reserve is not a sign that the estimate was drawn up badly. It is a sign that it was drawn up realistically: any renovation, especially in a resale flat, carries a degree of unpredictability, and an honest estimate accounts for it up front rather than hiding it behind “you’ll pay extra as it comes up”.

How to check an estimate before signing

Before signing off on an estimate and moving on to the contract, it is worth checking several things:

• consistency with the design — every item in the estimate should correspond to the scope fixed in the design documentation;
• labour and materials kept separate — if the cost of labour and materials is merged into a single sum, there is no way to verify either part;
• units of measurement — square metres, running metres, individual units: without them, an item cannot be checked independently;
• no vague wording — “additional works as needed” without an approval procedure is a source of future extra charges.

An estimate that has passed this check becomes an annex to the contract — it is exactly what the clauses on staged payment and the approval of extra works refer back to. How the rest of the contract is built around the design and the estimate is shown in the article a renovation contract.

The main point

A renovation cost estimate works as a real tool only when it is itemised, built on a finished design, includes a reserve for unforeseen works, and has been checked before signing. Such an estimate does not just fix a price — it lets you control the budget at every stage and compare contractors on equal terms. How to budget a renovation and work with an estimate at every stage — from design to handover — is covered in the course “Home of Your Dreams”.