The specification's role in the tender package
The specification is the technical document of the contract. Where the administrative conditions govern the administrative and financial terms of execution, the specification describes what must be done technically and to what requirements. It is written package by package: each contractor consulted receives only the specification for its own package.
Its contractual force is total. Once the contract is awarded, its requirements bind the contractor. If it calls for C25/30 concrete and the contractor uses C20/25, the contractor is in breach. If the specification is silent on the point, the contractor may use the concrete of its choice and the economist will have no ground to object.
That is why writing the specification is a technical and legal responsibility of the first order for the design team, and particularly for the economist coordinating production of the tender package.
ℹ The specification and the design team's liability In the event of damage or a dispute arising from poor execution, the specification is one of the first documents examined. If the defect complies with the specification — which was itself deficient — liability can run back to the design team that wrote it. A rigorous specification is therefore also a protection for architect and economist.
The standard structure of a specification
A specification follows a standard set of sections, adapted to each trade but built on the same skeleton. That consistency between packages makes it easier for contractors to read and reduces the risk of omission.
| Section | Typical content | Example: structural package |
|---|---|---|
| 1. General matters | Scope of the package, reference texts (standards, codes of practice, regulations), documents to be supplied before execution | Eurocode 2, the foundation code of practice, the general conditions of contract, the engineer's approved drawings |
| 2. Common requirements | General conditions of execution, coordination with other packages, protection of adjacent works, health and safety | Planning of excavations with the external works package, openings to be formed for the services packages |
| 3. Requirements item by item | For each item: materials specified, methods, execution tolerances, conditions of installation | C25/30 concrete at 28 days, high-yield reinforcement to the engineer's drawings, verticality tolerance ± 5 mm/m |
| 4. Testing and inspection | Tests to be carried out, frequency, acceptance thresholds, approved bodies, traceability documents | Concrete strength tests, one cube per 50 m³; compaction testing of fill |
| 5. Documents to be handed over | The as-built file, technical data sheets, test certificates, manufacturers' warranties | Concrete product sheets, test results, reinforcement supplier certificates |
Section 3 is by far the bulkiest. For a structural package on a five-storey building it can run to 15 to 25 pages. For a mechanical services package on an office building it can exceed 40.
Specifying with precision: the basic rule
Always quantify the requirement
The golden rule is never to use a vague adjective without a measurable value beside it. "Good acoustic quality", "sufficient strength", "careful finish" are contractually unusable: every contractor will read them differently.
Requirements must be expressed in verifiable numbers: concrete strength in MPa, sound reduction in dB, thermal resistance in m²·K/W, exposure class to the standard in force. Those values may come from the standards themselves or be set by the engineer on the basis of calculation.
Reference the applicable texts
Every technical requirement must point to the text that founds it: European or national standards, codes of practice, technical approvals or research-body papers. That serves two purposes: it makes the source of the requirement clear, and it lets the contractor verify compliance with its own products and processes.
Specify without unduly restricting competition
Describing the performance expected precisely is legitimate — air permeability at or below 0.6 air changes per hour, for example. Naming a single product or brand with no alternative is problematic, because on public projects it can restrict competition unlawfully.
The usual practice is to write "product of type X (reference brand) or a justified technical equivalent", stating the equivalence criteria the contractor must demonstrate in its technical statement.
Interfaces between packages: the most sensitive point
Interfaces between trades are the principal source of dispute during construction and at handover. Wherever two packages share a work area or an item, the boundary of responsibility must be defined explicitly in the specification of each of them.
The classic interfaces never to forget
- Structure with mechanical and electrical services: openings in concrete walls and floors are formed by the structural package on the services engineers' instructions. The structural specification must state who supplies the setting-out drawings and by when, and who bears the cost of making good a mispositioned opening.
- Roof structure with covering: supplying and fixing flashings, closures and roof accessories is sometimes shared between the two packages. The boundary must be explicit.
- External joinery with façades: fixing the windows (by the joiner), the reveal linings (by the façade contractor) and the air-tightness layer (by whom?) are classic grey areas.
- Tiling with plumbing: shower thresholds, channels and the upstands of the waterproofing under the tiling sit on the boundary of the two packages. Overlooking this generates frequent damp defects.
How to write an interface clause
For each interface identified, the specification of each package concerned should carry an explicit clause of the form: "The contractor for this package carries out [item X] up to [physical boundary Y]. Item [Z] falls to package [N], to which the contractor for this package must issue [document, drawing or dimensions] no later than [date]."
Specification and level of specification: from entry level to high end
A specification is not universal; it must be calibrated to the level adopted for the project. For social housing the requirements will cover standard materials complying with the codes of practice. For a high-end building they will add requirements on finishes, on acoustic and thermal performance, and possibly on bio-based materials.
That gradation has a direct effect on the prices tendered, and therefore on consistency with the pricing schedule the economist has drawn up. A high-end specification paired with a schedule calibrated on standard prices mechanically produces offers above the estimate. It is a frequent inconsistency the economist must catch and correct before the tender documents go out.
Frequent errors in drafting
| Frequent error | Concrete consequence | Good practice |
|---|---|---|
| Specification copied from an earlier project without adaptation | Requirements that cannot be applied, inconsistency with the drawings, risk of dispute | Systematic rereading against the final drawings before issue |
| Vague, unquantified requirements ("good quality") | Divergent readings between contractors, offers not comparable | Always put a number on it: strength, acoustic performance, exposure class |
| A brand specified with no equivalent | Unlawful restriction of competition on public projects, fewer offers | Always add "or equivalent" with precise equivalence criteria |
| No requirements written for the interfaces between packages | Dispute over who does what: ducts, chases, fixings | Define the boundary explicitly at every critical interface |
| Standards and codes of practice out of date | Obsolete requirements, non-compliance | Check the publication dates of the reference texts cited |
| Specification not coordinated with the pricing schedule | Items described in one and absent from the other | Cross-read specification against schedule, package by package, before issue |
ℹ The unadapted generic specification: a real risk Many practices keep model specifications written for a standard project and reuse them by simply changing the project name. Without a thorough rereading against the new project's drawings, such documents invariably contain requirements that cannot be applied, references to elements that do not exist and omissions on the specifics of the site. The minimum rule: every specification must be reread package by package, against the final drawings, before it goes to contractors.
Specification writing at Quostra
Quostra produces specifications adapted to each project, from the architectural drawings and the engineering layouts available. The drafting covers the ordinary packages — structure, finishing trades, finishes, external works — with particular attention to interfaces and quantified performance requirements. For specialist packages such as high-performance mechanical services, electrics or specific equipment, Quostra coordinates the drafting with the engineers concerned.
Every specification Quostra delivers is reread for consistency against the corresponding pricing schedule before issue, so that the work described and the financial items correspond.
You have better things to do. Submit your project on quostra.com and an economist writes your specification, coordinated and adapted to your project.
In summary
The specification is the contractual document that defines what each contractor must build. It follows a five-section structure — general matters, common requirements, requirements item by item, testing, documents to be handed over — and rests on two fundamental rules: quantify every requirement, and define the interfaces between packages explicitly. A rigorous specification is at once the best instrument for steering the site technically and the best contractual protection for client and design team.