Where APD sits, and why it matters
APD holds a particular place in the sequence. Behind it, ESQ and APS have defined the project and tested whether it is economically feasible. Ahead of it, PRO and DCE will produce the contractual documents that go out to tender.
APD is therefore the last design stage before the definitive contractual commitments: the design team's commitment on cost at its close, the client's commitment in lodging the planning application, and the progressive commitment towards construction.
What changes between APS and APD
| Technical options | APS: broad directions. APD: settled choices with sizing data, insulation thickness, duct sections, roof structure type, foundation depth. |
|---|---|
| Economic precision | APS: a global estimate at ±15–20 %. APD: quantities measured element by element at ±10 %, with a definitive commitment. |
| Planning application | APS: not enough data for the application. APD: the complete planning file is produced, site plan, floor plans at 1:100, elevations, sections and description. |
| Coordination of consultants | APS: general coordination. APD: precise coordination between packages, structure and façade interfaces, builder's work openings for services. |
| Contractual liability | APS: a provisional commitment on cost. APD: a definitive commitment, and the basis on which any penalty is calculated. |
The APD deliverables
Architectural deliverables
- ℹ Floor plans, sections and elevations at 1:100: the definitive drawings that make up the planning file. Every opening is dimensioned, floor-to-ceiling heights confirmed, principal builder's work openings shown.
- ℹ Outline specification of the works: a technical description, package by package, of everything provided for. It is the textual base from which the PRO specifications will be written.
- ℹ Planning file: the application form, the planning drawings, site plan, floor plans, elevations, roofs, contextual view and graphic document, the descriptive note, and the preliminary thermal certificate where applicable.
- ℹ First report of the technical control body: on public-access and high-rise buildings, the control body issues a first report at APD. Its observations must be taken up before the application is lodged.
Consultants' deliverables
- ℹ Principle notes by technical package: mechanical and plumbing, covering heating, ventilation and hot water; electrical, covering the load assessment and supply arrangement; structural, covering the foundation system, structure type and loadings.
- ℹ Principle drawings by package at 1:100: schematic layouts of the services, location drawings for the plant rooms, and first coordination drawings showing the interfaces between packages.
- ℹ APD estimates by technical package: each consultant produces its own package estimate, which feeds the economist's overall APD quantities.
The APD quantities: the central cost deliverable
The APD quantities are the most structured economic document of the design stages. Unlike the APS estimate, built on ratios by trade, they descend to the level of individual elements: measurable units, square metres, cubic metres, linear metres or lump sums, each carrying a unit rate.
From an APS estimate to APD quantities: descending to individual elements
APS estimate, by trade: structural works 450,000 € excluding VAT; external joinery 85,000 €; mechanical services 120,000 € and so on.
Structural works, 200 mm reinforced concrete slab: 480 m² × 85 €/m² = 40,800 €
Structural works, 200 mm reinforced concrete wall: 340 m² × 120 €/m² = 40,800 €
Structural works, 400 mm circular column: 18 no. × 1,200 € = 21,600 €
External joinery, single-leaf aluminium window 1 × 1.2 m: 24 no. × 850 € = 20,400 €
This level of detail exposes the items that carry the budget and allows targeted trade-offs where the envelope is exceeded.
Well-built APD quantities are accurate to ±10 %. That is the precision the design team's commitment to the forecast cost needs in order to be credible.
The definitive commitment: what is contractually at stake
Under loi MOP, the end of APD is the moment the design team enters its definitive commitment to the forecast works cost. That commitment is formalised in a contractual document and becomes the reference for the rest of the operation.
| Usual tolerance | ±10 % between the APD forecast cost and the value of the signed contracts. Beyond that, the design team may be held answerable for the overrun. |
|---|---|
| Penalties | Where the overrun is attributable to the design team, an error in the quantities, an item omitted, a poor valuation, penalties apply to the construction stage fees. |
| Second commitment | Once the works contracts are signed, the design team enters a second commitment on the updated forecast cost. That figure governs the handling of variations during construction. |
| Outside causes | Overruns arising from outside events, material inflation, a change of brief by the client, discoveries during excavation, are not attributable to the design team. |
Under loi MOP the design team's final remuneration is not fixed when the contract is signed. It is settled at the end of APD, on the definitive forecast works cost. A project that turns out more expensive than envisaged at the bidding stage can therefore generate higher fees, and also penalties where the overrun is the design team's doing.
APD and the planning application: what to watch
The planning file produced at APD must take up every regulatory constraint identified during the design stages. Several points deserve particular attention.
- ℹ Conditions attached to the permission: requirements from the heritage architect, the fire service or the regional environment authority can force design changes after the application is lodged. Those changes feed back into the APD work and can affect the quantities.
- ℹ Floor area and footprint: conformity with the local plan must be checked. Calculating the regulated floor area, excluding the thickness of insulated external walls and unusable basements, is a frequent source of error.
- ℹ Thermal and environmental certificates: the certificate confirming that the thermal regulation has been taken into account must be produced at application stage. New buildings do not obtain permission without it.
- ℹ Fire safety note: mandatory for public-access buildings. It is examined by the safety commission and can force design changes, compartmentation, smoke extraction, escape routes.
Coordination at APD: the critical interfaces
APD is the stage at which the interfaces between technical packages must be identified and resolved. An interface left unresolved at APD becomes a problem on site, and a source of variations.
| Structure and façade | Openings in concrete walls for the joinery, the junction between concrete frame and cladding, thermal break details: all to be coordinated between the structural consultant and the architect. |
|---|---|
| Structure and mechanical services | Risers for ductwork, suspension points for services at high level, plant rooms and their area, height and access: all to be sized and confirmed by the structural consultant. |
| Mechanical and electrical | Power supplies to the mechanical plant, air handling units, heat pumps, ventilation plant, to be coordinated between the mechanical and electrical consultants. |
| Architect and economist | The schedule of elements in the APD quantities must match the drawings. Anything drawn but not measured is an omission, and an overrun waiting to appear at tender. |
What Quostra takes on at APD
The APD quantities are the most structuring cost deliverable of the design stages. Producing them takes several days of exacting work: measuring the elements off the drawings, applying unit rates, coordinating with the consultants, checking that the whole holds together. It is also the document that most directly engages the design team's liability.
ℹ Quostra, the construction economist on demand Cost estimates, pricing schedules, developer appraisals, summary notes. The deliverables that take you days today, taken on by a dedicated economist. You have better things to do. Submit your project and an economist takes over. → quostra.com
Sources: Léonard Hamburger, Maître d'œuvre Bâtiment, 3rd ed., Eyrolles, 2016 · Yves Widloecher and David Cusant, Manuel d'analyse d'un dossier de bâtiment, 2nd ed., Eyrolles, 2018.
Reference basis of the figures
The ratios per square metre and per unit on this page are stated in January 2026 values. They were updated from January 2025 values, the basis retained for this whole group of articles, 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.
Global amounts quoted in worked examples, along with rents, running costs and revenues expressed per year or per night, stay at their original 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.