How to Write a UK Structural Specification
Structure, national specifications, the project layer and the coordination that holds it together
Structural specifications are mostly written by reference, and that makes the project layer the whole job. This guide sets out a workable structure, the national specifications and standards to cite, what the project-specific part must add, how to coordinate it with the drawings, calculations and architect's specification, and how to handle contractor-designed elements, testing and the move from tender to construction issue.
National specifications supply the standard clauses. The project layer states every choice that is particular to the job.
What is a structural specification and how should it be structured?
A structural specification states the materials, workmanship, testing and design information that the drawings cannot carry, so that the contractor can price and build the structure the engineer designed. In UK practice it is built mostly by reference to national specifications, with a project-specific layer for everything particular to the job.
The drawings show geometry, sizes and details. The calculations record how the design was checked. Neither tells a contractor what quality of work is required, how it will be inspected or who is responsible for each piece of design. That is the job of the specification. For a structural engineer it is also a risk document: an ambiguous clause, a missing hold point or an out-of-date standard reference tends to surface on site, when the cost of correcting it is highest.
Most UK structural specifications work by reference. Steelwork points to the NSSS, concrete to the NSCS, piling and embedded walls to the ICE specification, and highway structures to the Specification for Highway Works. Beneath those sit the execution and materials standards. The engineer's writing effort goes into the project layer: the amendments, options and project data. That is where the engineer's judgement shows, and it is where specifications fail.
A workable structure has five parts. The proportions vary with the job, but the order rarely does.
- 01
A. General and design information
Scope, design basis, design responsibilities, order of precedence, tolerances philosophy, submissions and approvals.
- Content
- Standards and editions, design working life, consequence class, design responsibility matrix
- Risk
- Conflicts with architect's preliminaries
- 02
B. Materials and workmanship by reference
Steelwork to the NSSS, concrete to the NSCS and BS 8500, piling to the ICE specification.
- Content
- Title, edition, revision and annexes called up
- Risk
- Unversioned references
- 03
C. Project amendments and options
Every entry that differs from the national specification or fills a choice it leaves open.
- Content
- Execution Class, exposure and cover, finishes, tolerances, systems
- Risk
- Choices left at default
- 04
D. Testing, inspection and records
Who tests, how often, what is witnessed, what stops work.
- Content
- Hold points, sampling, acceptance criteria, records
- Risk
- Inspection assumed, not stated
- 05
E. Contractor design
The portions the contractor designs, with the brief for each.
- Content
- Design brief, loads, interfaces, review and returns
- Risk
- Responsibility implied
Part A frames everything else. Part B adopts national specifications by reference. Part C is the project layer. Parts D and E set out how the work is proven and who designs what.
The five parts can sit in one document or be divided between trade sections that mirror the architect's specification. The architect's specification is usually organised by CAWS work sections or a similar classification, and the structural engineer's document should map to it so that nobody has to hunt. Whichever route is chosen, state at the front which document governs where the two overlap.
Which national specifications and standards can you reference?
Reference NSSS 7th Edition, 1st Revision for building steelwork, NSCS 5th Edition for concrete frames, the ICE SPERW 3rd Edition (2016) for piling and embedded retaining walls, BS 8500 for concrete durability and specification, and BS EN 1090 and BS EN 13670 for execution. State the edition every time.
The advantage of referencing a national specification is that its standard clauses are written, reviewed and understood by the contractors who work to them. The cost is that the engineer must know what each one covers and where it stops. The table below summarises the main documents as verified at the date of this guide.
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| Document | Current position | Covers | Note for the engineer |
|---|---|---|---|
| NSSS (BCSA) | 7th Edition, 1st Revision, launched 3 October 2023 | Fabrication and erection of building steelwork, EXC2 with EXC3 annexes | Mandatory RQSC clause. Annex J covers sustainability. See the NSSS guide. |
| NSCS (CONSTRUCT) | 5th Edition, launched July 2025, web-based | Concrete frames in buildings, complying with BS EN 13670 | Standard clauses plus project clauses by exception. Access is through the NSCS website, which requires a login; check the access terms there. |
| ICE SPERW | 3rd Edition, 2016 | Piling and embedded retaining walls, in three parts | Part A advisory, Part B specification, Part C notes for guidance. Provides for a project specification. Pre-dates second-generation Eurocode 7. |
| BS 8500 | 2023 revision | Specifying concrete: complementary British Standard to BS EN 206 | The 2023 changes widened the cementitious materials available, including multi-component cements. Check exposure and cover entries. |
| BS EN 1090-1 and -2 | Referenced by the NSSS | Conformity assessment and technical requirements for steel structures | Contains options to be selected. Check the current status of any revision. |
| BS EN 13670 | Referenced by the NSCS | Execution of concrete structures | Check the current edition and any revision. |
| Specification for Highway Works | National Highways, with local amendments | Highway structures including steelwork and structural concrete series | For highway and some bridge projects only. |
Check the current edition before every issue. Several of these documents have changed recently or sit alongside standards that are about to change.
How to cite a national specification
Cite the title, edition and revision, and say which annexes are called up. Add a sentence that the project specification amends the standard by exception and set an order of precedence. SPERW is explicit on this point: the FPS describes it as intended to be the UK national standard specification for piling and embedded retaining walls, with clients and designers referring only to it so that its clauses need not be reproduced, and with special amendments made through a project specification. The NSCS has the same pattern, with standard clauses and project specification clauses that detail any amendments by exception.
What no national specification covers
Timber, masonry, cold-formed steel and many specialist systems do not have a single UK specification of equal standing, and are normally covered by a combination of product standards, manufacturer data and in-house clauses. Specify these deliberately and name the controlling standards, rather than assuming a general reference will do. This guide does not attempt to cover them. Whichever material is used, the references must be consistent with the design standards used in the calculations, which is why the transition to second-generation Eurocodes matters for every reference in the document: see Second-generation Eurocodes: what to change in your specifications.
What must the project-specific part add?
The project-specific part must record the design basis, state every choice the national specifications leave open, set tolerances and finishes where the project needs more than the default, define testing and hold points, and state the information the contractor must supply.
A national specification is written for a typical project. The project-specific part is where the engineer states how this project differs from typical, and fills in the data that the national specification cannot know. Most gaps in structural specifications are entries that were never made.
Design basis and design information
Start with the design basis: the design standards and their editions, the design working life, the consequence class the structure was designed to, the exposure and the principal loading assumptions. This is the information any contractor-designed element will need, and it is also what a later engineer or checker will want. State the standards used for design, not only the execution standards, since first and second-generation Eurocodes will coexist until 30 March 2028 and should not be mixed within one design without a decision. IStructE guidance cautions against mixing them.
Choices by material
The detail depends on the material. The table below lists the entries that most often need to be made, with illustrative wording only. Treat it as a prompt for the engineer's own decisions, not as recommended values.
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| Material | Entries the project must make | Illustrative wording |
|---|---|---|
| Steelwork | Execution Class by element, grades and sub-grades, connection design split, corrosion system and durability, fire protection interface, special tolerances, Annex J | EXC2 throughout. Connections by contractor to the schedule of design forces. |
| Concrete | Exposure classes, designated or designed mixes, cement and combinations, nominal cover, finishes, tolerances, formwork and striking, curing, embodied carbon limits | Foundations: designated concrete selected for the assessed ground chemistry. Elements exposed to weather: cover and mix as scheduled. |
| Piling and walls | Pile type and design responsibility, working loads, tolerances, testing regime, instrumentation, ground information status | Contractor-designed piles to the loads and settlement limits in the design brief. |
| Masonry and other | Controlling standards, mortar designations, movement joints, lintel and support arrangements, who designs restraint | Restraint details by the structural engineer. Lintels selected by the contractor from the manufacturer's tables. |
These are prompts, and the wording is illustrative. Each entry should be checked against the current edition of the national specification for the material.
Tolerances, finishes and sustainability
Tolerance clauses are among the most contested entries because other designers rely on them. Where cladding, lifts or finishes depend on tighter structural tolerances than the national specification gives, write them in, and write in who checks them and when. For concrete, state the finish class and, where visual concrete is required, how it will be agreed. Sustainability entries are growing in importance: the NSSS has Annex J for steelwork, and the NSCS 5th Edition places greater emphasis on embodied carbon and responsible sourcing. State what the project requires, such as EPD submission, cement combination limits or reuse, and who verifies it.
Information the contractor must supply
Close the project layer with the submissions. List the shop drawings, models, calculations, method statements and test records the contractor provides, with the review period and what a review does and does not mean. The contractor's design returns, covered below, belong here.
How do you coordinate it with drawings, calculations and the architect's specification?
Put each requirement in one authoritative place, state the order of precedence, make drawing notes refer to the specification, and agree with the architect who specifies each interface item. Calculations are the basis of design and are not normally contract documents.
A structural specification fails most often at its edges. The same requirement is written twice, with different words, in the drawing notes and the specification. The architect's specification includes a structural item the engineer has not reviewed. A contractor-designed element appears in the drawings but not in the specification. Coordination is a set of comparisons, and the order below makes them cheaper.
Compare, in this order
- Identity. Do element names, tags and grid references on the drawings match those used in the specification?
- Standards. Does every standard cited in the specification match the design basis used in the calculations, with the same edition?
- Responsibility. Does every contractor-designed element in the drawings and the matrix have a clause, a design brief and a list of returns?
- Interfaces. Do the architect's, services and structural documents agree on who specifies fire protection, fixings, fire-stopping and builder's work?
- Tolerances. Do the tolerances the façade and finishes designers assume match what the specification will deliver?
- Status. Does every tender-stage placeholder have an owner, a date and a resolution before construction issue?
Run the comparisons in this order. Each one removes a category of contradiction before the next is attempted.
Drawings and calculations
Drawing notes should refer to the specification, not restate it. A general note on a drawing that says "paint to specification" is fine. A general note that gives half the system is a second, weaker copy of the requirement. State in the specification which governs when documents conflict. Calculations record how the design was checked. They are normally not contract documents, but they supply the loads, deflection limits and assumptions that a contractor-designed element needs, so the numbers in the design brief must be traceable to them.
The architect's specification
Several structural items sit in the architect's document: masonry and lintels, screeds and finishes on structure, fire-stopping and cavity barriers at structural interfaces, and builder's work in connection with services. Agree who specifies what and write it down in both places. The same applies to fire protection of steel and corrosion protection of exposed structure, where the architect's finishes and the engineer's requirements overlap. A design responsibility matrix is the usual way to record the allocation.
Contractor-designed portions
The elements most often designed by the contractor in structural work are steel connections, precast concrete, post-tensioned slabs, piles and temporary supports for the façade. For each, the specification needs a design brief with the loads, deflection and movement limits, interfaces and the design standards, a statement of what the contractor returns (calculations, drawings, certificates) and when, and a statement of what the engineer's review covers. A clause that says "contractor to design" without those inputs is not a design allocation. The connection question is developed in Steel connection design responsibility, and the general principles in the guide to contractor-designed portions and performance specifications. The contract determines what the allocation means legally, so check the CDP provisions of the form in use. Take legal advice on the exact wording for each appointment.
How do you handle testing, tender issue and common failures?
Define who tests what, how often, what is witnessed and what stops work, without duplicating the frequencies in the national specification. Issue a complete specification at tender, control changes to construction issue, and watch for the failures that recur: stale references, ownerless placeholders, duplicated requirements and unallocated design.
Testing and inspection
The national specifications supply routine inspection and testing requirements, including frequencies for welds and concrete. Do not copy them. Instead state what is particular to the project: additional or independent testing, hold points where work stops until the engineer has inspected, witness requirements, the records to be retained, and the criteria for acceptance and rejection. Say who appoints the testing organisation and who receives the results. A hold point with no named recipient and no notice period is not enforceable in practice.
Tender issue and construction issue
The tender specification must be complete enough to price. That does not mean every detail is final, but every unresolved item should be identified as a provisional allowance, an option or an information requirement, with an owner. Open placeholders are costly: see TBCs in specifications at tender. The construction issue should be the same document with the placeholders resolved and the changes recorded. Use a revision record and a change log so the contractor can see what moved, and see specification change control for the discipline. On a higher-risk building, the structural information is likely to form part of what is submitted at Gateway 2 and later gateways, and the specification must stay consistent with the calculations and drawings supplied. Check the current submission expectations with the principal designer and the IStructE Building Safety Act guidance.
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| Failure | Typical cause | Where to catch it |
|---|---|---|
| Standard reference out of date | Master not reviewed since the last edition | Pre-issue review of every standard against the design basis |
| Requirement stated twice, differently | Drawing note copied from the previous job | Drawing notes refer to the specification, never restate it |
| Contractor-designed element with no brief | Responsibility stated on drawings only | Responsibility matrix compared with clauses |
| Choice left at default | Project entries not completed | Checklist of entries by material before issue |
| Hold point with no owner | Testing clause copied from the national specification | Named recipient and notice period in every hold point |
| Placeholder reaches construction issue | No owner or date assigned at tender | Open items list closed before construction issue |
Each failure has a place in the process where it could have been caught. The pre-issue review is the last one.
What audits find
Avoice's State of UK Specifications 2026 found internal contradictions in 94% of the specifications it analysed at contract issue, orphan references in 88%, leftover master content in 82% and open TBCs in 76%. The analysis was of architectural specifications, but the mechanisms are the same in a structural document, and the full figures and definitions are in Most common specification defects at contract issue. For a checklist applicable to any discipline, use the pre-issue technical review checklist, and see why specifications fail the same way in every practice for the root causes.
Questions engineers ask about structural specifications
What should a UK structural specification contain?
General and design information, materials and workmanship by reference to national specifications, project-specific amendments and options, testing and inspection requirements, and the brief for any contractor-designed portion. It should state its order of precedence and the editions of every standard cited.
Which national specifications do structural engineers reference?
The NSSS for building steelwork, the NSCS for concrete frames, the ICE Specification for Piling and Embedded Retaining Walls, and the Specification for Highway Works for highway structures, with BS 8500, BS EN 1090 and BS EN 13670 beneath them.
What is the current edition of the NSCS?
The 5th Edition, launched in July 2025. It complies with BS EN 13670, is web-based and contains standard clauses and project specification clauses that record amendments by exception.
Is the ICE piling specification still current?
The 3rd Edition of the ICE Specification for Piling and Embedded Retaining Walls was published in 2016, and no newer UK edition was found when this guide was written. It pre-dates the second-generation Eurocode 7, so check it against the design standard used..
Who writes the structural specification, the engineer or the architect?
The structural engineer normally writes it for structural elements, while the architect's specification covers architectural elements. Items that overlap, such as fire protection of steel and masonry support, should be allocated in both documents and recorded in the design responsibility matrix.
What should be different between a tender and a construction issue?
The tender issue must be complete enough to price, with unresolved items identified as allowances, options or information requirements. The construction issue resolves them and records every change, so the contractor can see what moved.
Where Avoice fits
A structural specification is a coordination problem as much as a writing problem, because the same facts live in drawings, schedules, calculations and a second specification.
In Avoice, the office master holds the practice's governed library of structural clauses and the standard wording for adopting national specifications by reference. Practice Rules can require every standard reference to carry its edition, and standards sets keep the list of standards a specification may cite under control. The pre-issue Technical Review compares the specification against schedules and drawings, which catches a drawing note that conflicts with a clause, and Avoice now writes structural as well as architectural and building services specifications. Avoice structural and MEP specifications are structured to CAWS or Uniclass 2015, the same as architectural specifications.
The engineer still decides the design basis, the Execution Class and the allocation of design responsibility. Software holds the structure, compares the documents and flags the mismatch before the contractor finds it.