Placing the measure in the economic cycle
Before going into detail, it helps to understand what distinguishes the developed-design measure from the economist's other outputs, and why it occupies such a central place.
| Criterion | Outline estimate | Developed-design measure |
|---|---|---|
| Working basis | Ratios per m², sketch drawings | Measurement item by item, developed drawings |
| Precision | 20 to 30 % | 10 to 15 % |
| Level of detail | By family of works | By trade, by item |
| Production time | 1 to 2 working days | 3 to 6 days depending on complexity |
| Principal use | Confirming feasibility for the client | Technical trade-offs, basis for the tender package |
The developed-design measure marks the move from a logic of global ratios to a logic of measured quantities. The economist is no longer estimating a cost per square metre of usable area: they are measuring, on the drawings, the real quantities of work to be carried out and applying reference unit rates to them. That change of method is what takes the uncertainty from 30 % down to 10 to 15 %.
ℹ Worth knowing In practice the measure is often carried out in two passes: an initial pricing early in the stage to steer the technical choices, then a refined update at the end of the stage once the drawings are stable. It is that final version which serves as the basis for the tender package.
Structure by trade
A developed-design measure is organised by trade, that is by contractor speciality. This mirrors the future structure of the works contracts: each trade will become a distinct package in the tender documents.
The main trades
- Structure: earthworks, foundations, masonry, reinforced concrete, floors, stairs. Generally the heaviest package, representing 30 to 45 % of the total cost on new build.
- Roof structure and covering: timber or steel frame, roofing, waterproofing, rainwater disposal. The share varies widely with the type — flat roof against pitched roof.
- Façades and external joinery: external insulation, cladding, windows, doors, balustrades. On refurbishment this package can represent 20 to 30 % of the total.
- Technical packages — heating, ventilation, plumbing, electrics: heating, ventilation, cooling, sanitary services, power and data. These packages average 25 to 35 % of the total cost.
- Internal finishes: floor finishes, painting, suspended ceilings, internal joinery, sanitary fittings. Highly sensitive to the level of specification.
- External works and surroundings: external services, roads, parking, landscaping. Frequently under-estimated in the preliminary stages.
The level of detail expected
At developed design, each trade is broken into its principal items, with a measured quantity and a reference unit rate. This is not yet the level of detail of the technical specification, but the breakdown must be sufficient to confirm the technical choices and anticipate the trade-offs. The structural package, for instance, is not summarised as "masonry: 50,000 €": it details the foundations by type, the floors by construction, the stairs by number of flights.
A worked example: a five-storey residential building
Here is a structured example for a new-build residential building of 10 dwellings in reinforced concrete, in a suburban location.
| Trade / item | Unit | Quantity | Unit rate excl. VAT (€) | Amount excl. VAT (€) |
|---|---|---|---|---|
| Structure: general earthworks | m³ | 320 | 35.00 | 11,200 |
| Structure: foundations, strip footings | linear m | 85 | 420.00 | 35,700 |
| Structure: masonry to elevations, 200 mm block | m² | 640 | 95.00 | 60,800 |
| Structure: beam-and-block floors, 5 levels | m² | 1,250 | 78.00 | 97,500 |
| Structure: concrete stairs, 4 flights | no. | 4 | 4,200.00 | 16,800 |
| Industrial timber roof structure | m² | 210 | 85.00 | 17,850 |
| Interlocking tile covering | m² | 210 | 65.00 | 13,650 |
| Façades: monolayer render | m² | 480 | 42.00 | 20,160 |
| External joinery: PVC double-glazed windows | no. | 38 | 680.00 | 25,840 |
| HVAC: communal heat-recovery ventilation | lump sum | 1 | 28,500.00 | 28,500 |
| Plumbing: foul, surface and cold water per dwelling | no. | 10 | 4,800.00 | 48,000 |
| Electrics: power and data per dwelling | no. | 10 | 3,600.00 | 36,000 |
| Floor finishes: tiling | m² | 420 | 55.00 | 23,100 |
| Floor finishes: floating timber | m² | 380 | 48.00 | 18,240 |
| Internal painting | m² | 2,100 | 18.00 | 37,800 |
| External works and surroundings | lump sum | 1 | 22,000.00 | 22,000 |
| Contingency (8 %) | 43,869 | |||
| TOTAL EXCL. VAT | 560,209 |
How to read it: the unit rates are reference values for a suburban location in 2025. They include supply, installation and site overheads. All the measurement assumptions are documented in the body of the report.
The risks of a weak measure
An insufficiently rigorous developed-design measure is one of the leading causes of budget overrun on site. The trouble does not always come from the large packages; it more often hides in omissions, approximations and inconsistencies between disciplines.
Frequent omissions
- Demolition and strip-out, systematically under-estimated on refurbishment.
- Site constraints: difficult access, protection of neighbours, working in occupied premises.
- Interfaces between trades: who lays the ducts before the slab? Who cuts the chases for the electrical services?
- Temporary works: propping, excavation support, site set-up.
- Utility connection charges: often forgotten and hard to anticipate.
Inconsistencies between disciplines
A measure produced without coordination with the other engineering consultants is an incomplete measure. If the structural drawings are not aligned with the architectural drawings, or if the services layouts have not been incorporated, the economist cannot correctly quantify the works concerned. These inconsistencies usually surface when the tenders come in — too late to act without extra cost.
ℹ Point of vigilance A developed-design measure produced without structural drawings or services layouts cannot be regarded as reliable. If those documents are unavailable, the economist must say so explicitly and load their assumptions accordingly. A gap of 15 to 20 % between the measure and the tenders received is often the sign of a measure produced on incomplete drawings.
The measure as a decision tool
The real value of the developed-design measure lies not in the final figure but in the ability it gives to compare variants and take informed decisions while it is still cheap to change them.
Trade-offs are still open
At this stage the trade-offs remain possible and inexpensive. Replacing a flat roof with a pitched one, insulating internally rather than externally, choosing communal heating over individual systems: each of these decisions has a measurable budget impact that the measure quantifies precisely.
The effect on the quality of the tender package
A solid measure is the best guarantee of a good tender package. Specifications are easier to write when the quantities are known, pricing schedules are more precise, and contractors can price with less uncertainty — which translates directly into more competitive offers and fewer variations during construction.
Obtaining a developed-design measure from Quostra
Quostra produces developed-design measures for every project type: apartments, houses, offices, public buildings, refurbishment. The assignment goes to an experienced economist working from the documents submitted on the platform.
Documents needed to start:
- Developed architectural drawings — plans, elevations, sections — in DWG or PDF.
- Structural drawings where available; otherwise assumptions documented by the economist.
- Mechanical and plumbing layouts where available.
- The schedule of areas and an outline description of the specification sought.
The deliverable includes the complete breakdown by trade with quantities, unit rates and amounts, the assumptions set out, and a note on the principal risks identified. Indicative lead time: 3 to 5 working days depending on complexity.
You have better things to do. Submit your project on quostra.com and an economist produces your developed-design measure within 72 working hours.
In summary
The developed-design measure is the pivotal cost study of the project: more precise than the outline estimate, more operational than the tender package, it both confirms the definitive budget envelope and allows the last technical trade-offs to be taken before going out to tender. Its quality depends directly on the quality of the drawings supplied and on coordination between disciplines. Done well, it is the foundation the whole tender package rests on.
Reference basis of the figures
The figures on this page are stated in January 2025 values and have not been recalculated: this is a worked example of a measure, whose quantities, unit rates and totals must remain consistent with one another. Recalculating it item by item would break the arithmetic, which is the very subject of the article.
To bring them forward, apply the usual revision formula: updated value = page value × (BT01 for the month in question / 132.0). The BT01 all-trades index, published monthly by INSEE on its 2010 base, stood at 132.0 in January 2025 and 134.7 in January 2026, a coefficient of 1.0205.
The BT01 measures contractors' input costs, labour at 44.9 % and materials at 36.5 %, not the prices actually tendered.