How to Write an M&E Specification: A Field Guide for UK Building Services Engineers

What does an M&E specification contain, and how is it structured?

A UK M&E specification normally has seven parts: general requirements, system sections, performance, products and materials, installation and workmanship, testing and commissioning, and operation and maintenance. Each part has a different reader in mind and a different way of going wrong.

The seven-part order below is how most UK services specifications are organised, whether the document is a standalone M&E volume or a set of sections inside a combined project specification. Practices that classify by CAWS put system requirements in groups R to X and workmanship in the shared reference group Y. Practices that use Uniclass 2015 organise by system and product. The same seven questions apply either way, and the existing Avoice guide to MEP specifications covers classification and the architect interface in more detail. This guide stays with the internal construction of the document and the engineer's decisions.

Reference documents for the structure

BSRIA publishes Model Format for Building Services Specifications (BG 56/2016) as a reference for the arrangement of a services specification, and Design Framework for Building Services (BG 6/2018) for allocating design activity and deliverables. Both are paid BSRIA publications, so check the edition held in the office before citing either in an appointment or a specification. The BG 6 product page lists the contents and the editable proformas.

Keep the general requirements short and true

General clauses are where templates accumulate the most leftover text. Each paragraph should earn its place: if the project has no sprinklers, no district heating connection and no building management system, the general section should not refer to them. A short document that matches the project is easier to price and harder to contradict. Put each requirement in one authoritative place and refer to it from elsewhere. Pipework, ductwork and cable workmanship written once in a reference section and cited from each system section is easier to maintain than the same clause pasted five times with five slightly different tolerances.

Should each system be specified by performance or prescriptively?

Choose by system. Specify prescriptively where the consultant has completed the design, and by performance where the contractor completes it, then make the clause, the schedules and the responsibility matrix agree.

The choice between performance and prescriptive wording is a decision about who carries design risk and who owns the information. It is made system by system, because the same project usually has some systems fully designed by the consultant and others completed by a specialist after award.

Prescriptive: the consultant has completed the design

A prescriptive clause tells the contractor what to supply and install: sizes, routes, capacities, selected plant and the drawings that show them. The engineer owns the design and the contractor builds it. This is normal for heating and ventilation distribution designed to Stage 4 in full, for electrical distribution with final circuit schedules, and for fire alarm systems where the consultant has designed device positions. Prescriptive wording is safe only where the design information really is complete. A prescriptive clause on an incomplete design leaves the contractor entitled to ask for the missing information, and leaves the engineer responsible for supplying it.

Performance: the contractor completes the design

A performance clause states the result the system must achieve and the evidence that proves it, then leaves the solution to the contractor within stated limits. Plant selections, pipe sizing within a given pressure drop, controls software, packaged plant, lift and escalator installations and fire protection systems commonly sit here. The guide to contractor-designed portions and performance specifications covers the contract side. For services, a workable performance clause has five parts: the design conditions and inputs the engineer provides, the performance required, the standards the design must follow, the submissions required before manufacture, and the tests that prove the result on site.

The hybrid is the failure

The most common problem is a clause that does both jobs badly: it states a performance requirement and also names a product or a size that cannot achieve it. If the named product cannot meet the stated performance, the contract contains a contradiction and the engineer has to resolve it after award, usually at a cost. If a product is named, say whether alternatives are allowed and how equivalence will be judged. If a performance is stated, say which governs when the two disagree.

The same clause should be traceable to a row in the M&E design responsibility matrix and to a line on the equipment schedule. If it is not, the information the contractor needs is held in someone's head.

How do you coordinate the M&E specification with the architect's specification, drawings and schedules?

Give every requirement one authoritative home, cross-refer instead of repeating, and compare both specifications with the drawings and schedules before each issue. Most interface failures sit at six points: penetrations, builders' work, accessories, ceilings and risers, controls and commissioning.

The engineer and the architect issue separate documents that describe one building. Services problems on site cluster at the interfaces between those documents, so coordination needs to be a set of named checks, not a final read-through.

The interfaces that go missing

Penetrations and fire stopping. Fire stopping around services through compartment walls and floors is specified by someone, installed by someone and designed to match the fire strategy. If the architect's specification, the engineer's and the contractor's submissions each assume another party covers it, nobody does. Name one document, one product system and one installer. On a higher-risk building the number and dimensions of openings for pipes, ducts and cables are also a matter for change control; Gateway 2 and the Golden Thread for Building Services Engineers covers that.

Builders' work in connection. Holes, plinths, supports and access panels are often missing from both specifications or described in both with different responsibilities. Decide who forms the opening, who makes good, and who provides access.

Luminaires, switches, sockets and sanitary connections. The architect often selects them and the engineer specifies the supply and connection. Mounting heights, finishes and accessibility requirements must agree, and each item should appear once.

Ceilings, risers and plant spaces. Void depths, access hatches, riser sizes and plant room acoustics appear on architectural drawings, in the architect's specification and in the services design. A change in one needs to reach the other two.

Controls, commissioning and handover. Commissioning, witnessing, O&M manuals and asset data are needed for practical completion. Say which document sets each requirement and who is responsible for coordinating the sequence.

Drawings and schedules

The drawings and equipment schedules carry the numbers; the specification carries the obligations. A clause that says “as scheduled” is only as good as the schedule, so every tag in the specification should exist on a schedule and every scheduled item should have a clause or a reference clause behind it. Use one tag format across drawings, schedules, model and specification. A tag renamed on the drawings after the specification was written is how orphan references arise. Where the architect's specification and the engineer's are both issued to tender, a short coordination register listing each shared item, the document that governs it and the person who checked it is cheap insurance. The architect's design responsibility matrix guide and the pre-issue technical review checklist give the architectural side of the same checks.

Statutory duties sit on the document

Since 1 October 2023, designers in England carry duties under Part 2A of the Building Regulations 2010, inserted by SI 2023/911: regulation 11J requires design work to be planned, managed and monitored so that it complies, and regulation 11K sets further duties on designers. A services specification is design work, so a contradictory or vague one is a compliance risk as well as a commercial one. See Part 2A duty holders for how the duties are allocated.

What changes between tender issue and construction issue?

The tender issue has to be complete enough to price. The construction issue records everything that changed after award. Treating them as the same document is how scope gaps become variations.

A services specification is issued more than once, and each issue has a different job. Treating them as the same document, with the same level of completeness, is a common source of variations.

Tender issue: priceable and complete

The tender issue is the contractor's pricing basis. It should state extent, performance and design responsibility clearly enough that two tenderers will price the same scope. Open TBCs on plant capacities, equipment selections or control strategies move risk to the contractor's price or to a post-award variation. The TBCs in specifications at tender guide sets out how to find and close them. Where a decision genuinely cannot be made before tender, state the allowance, who decides and by when, instead of leaving a bare “TBC”.

Design responsibility handover to specialist subcontractors

Where the contractor completes the design, the handover of responsibility needs to be written down. The specification should say what design information the engineer has provided, what the contractor must design, what the contractor must submit and when, and what the engineer will review. Review is not design transfer: reviewing a submission to check it against the stated performance does not make the engineer the designer of the portion, and review comments that go beyond that purpose risk being read as design instructions. State the purpose of review in the specification and use the same words in the review stamps.

The contractor's design submissions should arrive with their inputs, calculations, selections and drawings in a form that can be compared with the performance clause. If calculations arrive after the plant has been ordered, review is a formality. Put the submission date before the order date.

Construction issue and after

After award the specification becomes a controlled document. Accepted alternatives, clarifications from the tender period and design changes should be consolidated into a construction issue, so that the installer, the commissioning engineer and the client are working from one version. Changes after that point need a record of what changed, why and who agreed it. The specification change control guide sets out a method, and the RIBA Stage 4 guide shows where the issues sit in technical design. On higher-risk buildings, controlled change has statutory consequences, covered in the Gateway 2 guide for building services engineers.

What are the most common failures in M&E specifications?

Most failures are repeats of the same few mistakes: copied project values, stale standards, implied responsibility, open TBCs on priced items, orphan references and tests without pass criteria. All are detectable before issue.

Audits of issued specifications show a consistent pattern. Avoice's State of UK Specifications 2026 review found internal contradictions in 94% of specifications at contract issue, orphan references in 88%, leftover master content in 82% and open TBCs in 76% (Common Specification Defects at Contract Issue). Those figures describe specifications generally, and services documents show the same defect types in recognisable forms.

Six failures that recur in services specifications

Copied plant from the last project. A clause that still carries the previous job's capacity, make or refrigerant is both a contradiction and a liability. Strip project values out of the master and make every value a deliberate entry.

Standards cited without an edition, or with the wrong one. Editions move during design. IET and BSI published Amendment 4 to BS 7671:2018 on 15 April 2026, and BS 7671:2018+A2:2022+A3:2024 was withdrawn on 15 October 2026. The 2025 edition of BS 5839-1 is listed as current by BSI. Approved Documents L and F take effect on 24 March 2027 for building work other than higher-risk building work, and on 24 September 2027 for higher-risk building work, per the published documents on gov.uk. Check whether the transitional arrangements apply to the project in hand. State the edition the design follows and check it at every issue.

Responsibility implied. Performance clauses that never say who completes the design, or prescriptive clauses with a line saying the contractor is responsible for the design. Both are arguments waiting for a programme delay.

Open TBCs on priced items. Plant capacities, equipment selections and control strategies left “to be confirmed” when the contractor prices.

Orphan references. “Refer to the services drawings” where the drawing was renumbered or never issued, or a clause that refers to a section that was deleted.

Tests without acceptance criteria. A list of tests with no pass values means practical completion is a negotiation. Say what is measured, to what method, against what value, and who witnesses.

A pre-issue gate for services

• ✓Every system in the specification appears on the drawings and schedules, and every scheduled system has a section.
• ✓Every performance clause states a result, the standard and the proof.
• ✓Every standard citation carries an edition checked within the current issue cycle.
• ✓Every row of the design responsibility matrix matches the wording of its clause.
• ✓No open TBC remains on plant capacity, equipment selection or control strategy.
• ✓Fire stopping, builders' work and access are each assigned to one document and one party.
• ✓Each test has a method, a pass value, a witness and a record format.
• ✓Operation and maintenance and handover requirements are dated against the programme.

For a practice running many projects, the cheapest control is a services master with one owner per discipline and a review cycle triggered by events such as a BS 7671 amendment or an Approved Document commencement. That is the same discipline described for architectural masters in keeping the office master up to date.

Questions engineers ask about M&E specifications

What should an M&E specification contain?

It should contain preliminaries and general requirements, a section for each system (heating, ventilation, cooling, electrical, public health, fire detection, controls and so on), the performance each system must achieve, the products and materials permitted, installation and workmanship requirements, testing and commissioning with acceptance criteria, and operation and maintenance information for handover. Each part should say who designs what.

Who writes the M&E specification?

On most projects the consulting building services engineer writes it, and the architect writes the architectural specification and leads coordination between the two. Where a mechanical or electrical contractor completes the design, the engineer writes a performance specification and design brief, and the contractor's design submissions then become part of the record.

Should an M&E specification be performance or prescriptive?

Both appear in most services specifications, chosen system by system. Specify prescriptively where the consultant has completed the design and the contractor builds it. Specify by performance where the contractor completes the design. Whichever is chosen, the clause, the schedules and the design responsibility matrix should say the same thing.

What is the difference between tender issue and construction issue for M&E?

The tender issue must be complete enough to price, with no open TBCs on plant or controls. The construction issue adds what changed after award: accepted alternatives, tender clarifications, the contractor's design submissions once reviewed, and any changes to requirements. Each issue should be dated and traceable to the one before it.

How do you stop the architect's and the engineer's specifications contradicting each other?

Give each requirement one authoritative home, cross-refer rather than repeat, and compare both documents with the drawings and schedules before every issue. The usual conflict points are fire stopping of service penetrations, builders' work in connection, luminaires and accessories, sanitaryware connections, ceilings and risers, and commissioning.

Which standards should an M&E specification cite?

The current edition of each standard the design relies on, stated in the specification and checked at every issue. In October 2026 that includes BS 7671:2018+A4:2026 for wiring, BS 5839-1:2025 for fire detection and alarm, and the 2026 Approved Documents L and F once they take effect. Do not carry editions forward from the last project without checking.

Where Avoice fits

Services specifications are written in several hands, against schedules that change weekly, so the work is mostly keeping documents aligned.

Avoice now writes building services (MEP) specifications alongside architectural ones, so mechanical, electrical and public health sections can be drafted in the same workspace and checked against the architect's sections. Avoice MEP and structural specifications are structured to CAWS or Uniclass 2015, the same as architectural specifications. The office master works as a governed library, so the clauses an engineering team reuses sit in one controlled place with an owner, and practice Rules can enforce things such as a stated standard edition in every citation or a named acceptance criterion in every commissioning clause.

The pre-issue Technical Review compares the specification with schedules and drawings, which is where open TBCs, orphan references and tag mismatches show up. The Compliance module and Construction Admin carry the project forward after issue, including spec change tracking. The engineer still decides the design, the performance values and who completes what. For the classification and interface side of services specifications, see How to write an MEP specification in the UK.