The outline-stage estimate: a project's first budget assessment

The outline-stage estimate is the first formalised pricing of a construction project. It comes at the moment when architectural intentions start to take shape, but before the drawings are developed enough to allow a detailed measure. Its role is to give a credible financial envelope from information that is still fragmentary: approximate areas, the construction types under consideration, the level of specification sought.

It is not a quotation. It is a decision-making instrument for the client: it lets them confirm that the project sits inside its zone of economic feasibility, identify which packages weigh most heavily on the budget, and commit — or not — to the next stage of design with their eyes open.

For the architect, it is also an internal framing tool. It lets them check that their design choices remain compatible with the approved budget, and anticipate the trade-offs that the developed-design stage will require.

ℹ When is an outline estimate commissioned? Typically after the first sketches or feasibility studies, before committing to developed design. Sometimes also ahead of a land purchase, to assess the cost of the construction envisaged on a site. It may equally be commissioned mid-design to test the economic impact of an architectural variant or a change of brief.

A well-structured outline estimate is not a single global figure. It breaks the project down by major families of works, shows how the cost is distributed, and states explicitly the assumptions adopted for each assessment.

• The breakdown by package or family of works: structure, roof and covering, façades, external joinery, technical packages — heating and ventilation, plumbing, electrics — internal finishes, external works and surroundings. This breakdown identifies where the budget is really at stake.
• The base assumptions: the areas adopted (habitable area, floor area, footprint), the construction types (reinforced concrete, timber frame, steel), the level of specification (standard, intermediate, high-end), and the ground conditions where known.
• The ratios applied: unit costs per square metre or per item, drawn from the economist's database, brought up to date for the local market and the anticipated tender date.
• Contingencies and provisions: at outline stage a contingency margin of 8 to 12 % is generally included to account for the uncertainties of the stage.
• VAT and fees: the estimate presents costs excluding VAT, with an indication of the applicable rates according to the nature of the works — new build, refurbishment, social housing.

It contains no detailed measurement; that only becomes possible from drawings of sufficient precision, developed-design level at the earliest. Nor does it cover the project's ancillary costs: design fees, ground investigation, technical control, structural warranty insurance, utility connection charges. Those are generally summarised in a separate whole-investment table.

To illustrate the structure of an outline estimate, here is a simplified example for a residential building of 320 m² habitable area undergoing heavy refurbishment in the Paris region, with sketch drawings available.

How to read the table: the bands reflect the uncertainty inherent in the stage. The lower bound corresponds to standard specification with normal site conditions; the upper bound builds in more conservative assumptions about site difficulty and specification level.

Producing one rests on two pillars: a database of ratios kept constantly up to date, and a close reading of the project by an experienced economist. It is the combination of the two that makes the result meaningful.

The ratios used at outline stage are built from experience of comparable sites, from sector databases — commercial price books, practices' internal databases, data published by the profession or by construction cost observatories — and from regular monitoring of the local market. They are differentiated by project type (apartments, houses, offices, public buildings, refurbishment), by geographic area and by specification level.

The economist does not simply apply a raw ratio. They adjust the assessment for several project-specific parameters:

• Architectural complexity: an intricate plan or numerous geometric constraints raise the cost of both structure and finishes.
• Ground conditions: special foundations such as micropiles or a reinforced raft can represent 15 to 25 % of the structural cost.
• Site access: in dense urban settings, logistical constraints — a narrow street, no room for a crane — feed straight through into cost.
• The existing fabric, on refurbishment: asbestos, lead, or structure in poor condition generates risks that are hard to price precisely at this stage.
• The programme: a tender expected in two years' time requires prices to be brought forward for material inflation.

In practice the economist starts by analysing the documents supplied — sketch drawings, brief, photographs, ground investigation where available — then breaks the project into families of works. For each family they select the best-fitting ratio from their database, adjust it for the correction factors identified, and calculate a lower and upper bound. They then add contingencies and present the result in a structured document with the assumptions set out.

ℹ What the economist needs in order to work To produce a sound outline estimate, the economist needs at minimum: sketch or existing-condition drawings, even approximate ones; a schedule of areas (habitable area, floor area, number of dwellings or square metres of offices); a precise location; and the level of specification sought. The more precise the inputs, the tighter the band. An estimate produced with neither drawings nor brief will necessarily be wider and less useful.

An outline estimate is a powerful tool, provided you understand what it can and cannot guarantee.

At this stage the expected precision is of the order of 20 to 30 %. That is inherent to the stage: the drawings are incomplete, the definitive technical choices are not settled, and the market conditions at tender are unknown. An outline estimate claiming a precision of 5 % would be misleading.

The band is not a defect of the estimate, it is its honesty. It reflects the real state of knowledge at this point in the project.

A client who signs a design appointment on the basis of an outline estimate cannot hold the architect or the economist responsible for an overrun if the conditions of the project change. The outline estimate supports a decision; it is not a contractual guarantee of cost. That only becomes possible when the works contracts are signed, at the end of the award stage.

The main risk is to take the lower bound as the reference budget and then run the project under permanent pressure. A well-advised client will take the middle of the band, or even the upper bound, as the working envelope, and keep a reserve for the unforeseen.

ℹ Good practice For a project whose outline estimate gives a band of 400,000 – 550,000 € excluding VAT, it is advisable to work with a reference envelope of around 500,000 €, and to hold a further client reserve of 5 to 10 % for risks the studies do not cover.

At Quostra the outline estimate is one of the most frequent assignments. It is produced by an experienced economist from the documents you submit on the platform: sketch drawings, brief, location, level of specification sought.

The delivery time is calculated automatically when the project is submitted. For a residential building or an ordinary office programme it is typically 72 working hours. For a complex or large-scale project the lead time is recalculated according to the volume of analysis required.

The deliverable comprises:

• The breakdown by family of works, with a lower and upper bound for each item.
• The assumptions adopted, set out and documented.
• The summary table with the total excluding VAT and an indication of VAT.
• A reading note explaining the principal factors of uncertainty identified.

You have better things to do. Submit your project on quostra.com and an economist produces your outline estimate within 72 working hours.

The outline-stage estimate is the first economic milestone of a construction project. Produced from calibrated ratios and a close analysis of the project's specifics, it gives a reliable budget band from which economic feasibility can be confirmed before heavier studies are commissioned. Its natural precision of 20 to 30 % is not a defect but a faithful reflection of how far the design has progressed. Read and used properly, it is the tool that prevents the most expensive framing errors.

Reference basis of the figures

The ratios per square metre and per item on this page are stated in January 2026 values. They were updated from January 2025 values, the basis adopted for the whole cocoon, using the BT01 all-trades index published monthly by INSEE on its 2010 base: 132.0 in January 2025, 134.7 in January 2026, a coefficient of 1.0205.

The global amounts quoted as examples, and any rents, charges or receipts expressed per year or per night, remain on their own basis: a building cost index does not apply to them.

To bring the ratios forward, apply the usual revision formula: updated value = page value × (BT01 for the month in question / 134.7). The BT01 measures contractors' input costs, labour at 44.9 % and materials at 36.5 %, not the prices actually tendered.