Expenditure on a construction site: the breakdown and the ratios

For an ordinary building, works expenditure typically divides as follows, as a percentage of the total works cost:

Structure	30–50 % of the works. The most variable item, according to ground conditions, the number of storeys and the construction method. It covers foundations and substructure, frame in concrete, steel or timber, masonry, roof structure, covering and waterproofing, and external joinery.
Finishing trades	35–45 % of the works. The item most influenced by the level of specification: partitions and linings, floor and wall finishes, internal joinery, plumbing and sanitary, mechanical services, rising sharply with the environmental requirements, and electrics, power and data.
External works and services	5–15 % of the works. Highly variable with the size of the site, the state of the existing services and the ground conditions.
Site set-up	3–6 % of the works. Site fencing, cabins, cranes and heavy plant, temporary services, safety and protection.

For each elementary item, a homogeneous unit of work, such as a square metre of reinforced concrete wall or of plasterboard partition, the contractor calculates a net cost comprising three elements:

Materials	The purchase price plus delivery to site. Note that the elementary quantities incorporate waste factors, breakage, cutting, offcuts, which increase the quantities above those actually in place.
Productive labour	The unit time, in productive hours per unit, multiplied by the hourly labour cost. That hourly cost includes the worker's gross wage AND the employer's social contributions.
Plant	The cost of plant directly attributable to the item: a provision for renewal or hire, maintenance, consumables. Plant used across the whole site, crane, cabins, is counted instead in site overheads.

The hourly labour cost is probably the figure least well understood by non-specialists. It is neither the worker's net wage nor their gross wage alone.

ℹ Hourly labour cost = annual net labour expenditure / annual productive hours

Where the annual net labour expenditure is the sum of gross wages plus employer contributions over the year, for all the firm's productive workers.

Why it is higher than the collective agreement rate

An entry-grade worker has a basic wage of 12.50 to 14.50 € an hour according to the collective agreement, with the gross hourly minimum wage at 12.31 € from 1 June 2026. But the employing firm's hourly cost is 23 to 28 €. The difference is explained by:

Employer social contributions, 40–45 % of the gross wage

Bonuses and allowances: seniority, travel allowances above the exempt thresholds

The gap between hours present and hours productive: a worker present 1,590 hours a year does not produce 1,590 hours; unproductive time, meetings, travel between sites, cleaning, reduces the effective denominator

An hourly cost of 25 € for a skilled tradesperson is a current reference value in the Paris region in 2026. In the provinces the values observed run between 22 and 27 € according to the trade and the applicable collective agreement.

Site overheads are expenditure directly tied to the site but not attributable to a particular item. They are either fixed, independent of the duration, or proportional to time and therefore to the duration.

Fixed costs	Site signage, erecting and dismantling the crane, installing the cabins and welfare facilities, temporary water and power connections, laying out the storage areas.
Time-proportional costs	Crane hire, monthly; welfare facility hire; water and electricity consumption; supervisory staff, site manager, contracts manager.

Expressed as a percentage of net costs, site overheads vary considerably with the nature of the site:

Finishing trades: plastering, painting, electrics	Roughly 6–10 % of net costs. Little heavy plant, light supervision.
Standard structural works	Roughly 10–18 %. Crane, formwork, a fuller supervisory team.
Complex structural works on a constrained site	Roughly 18–30 %. Set-up constraints, reinforced safety, difficult access.

Operation costs are added on top: ground investigation, surveying, approved technical control, site insurance, and the as-built and maintenance files. They generally represent 2 to 5 % of net costs.

Above net costs and site overheads, two further layers are added before reaching the selling price:

Head office overheads	The firm's running costs not tied to a particular site: the head office, service vehicles, administrative management, IT. They represent 8–12 % of the selling price.
Risk and profit	A provision for the site's risks, technical surprises, delay, supply difficulties, and the profit expected. The management sets the percentage: generally 6–10 % of the selling price. In a tight market, firms reduce it to stay competitive, sometimes dangerously.

At the end of the site the contractor produces an analytical account comparing real expenditure with the forecast in the offer. It is at once a profitability control and a source of data for improving future offers.

ℹ The indicators of the analytical account Margin = sums received less real direct costs. Gross result = margin less the head office overheads allocated. A positive result means a profitable operation. A negative one means a loss, even where the margin is positive, the margin may be insufficient to cover the overheads. The gaps between the risk allowance and the real result let the calculation parameters, hourly labour cost, elementary quantities, overhead coefficients, be updated for the next offers.

Related articles: How to estimate the cost of a project · The effect of materials on the budget · cost per square metre by building type · Construction costs and estimates

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ℹ The nature of the figures The orders of magnitude on this page are expressed as percentages of a total, not as amounts. They therefore do not drift with the building cost index and need no updating: it is the distribution that is the reference, not the level. The amounts those percentages apply to must be taken at the date of the study. To bring them forward, use the BT01 all-trades index published monthly by INSEE on its 2010 base, which stood at 134.7 in January 2026.

The nature of the figures quoted

The percentages and amounts quoted on this page are orders of magnitude for framing, not measurements. They illustrate mechanisms and proportions, and they substitute neither for a tender exercise nor for an estimate prepared on drawings.