CAWS Explained: The Common Arrangement of Work Sections

What is CAWS, and where did it come from?

CAWS, the Common Arrangement of Work Sections, is the UK convention for arranging specifications and bills of quantities into the same set of work sections. It was first published in 1987 and revised in a second edition in 1998.

The Common Arrangement of Work Sections was first published in 1987 as a working convention for the UK construction industry. Its stated purpose was to standardise, and to coordinate in detail, the way bills of quantities and specifications are arranged. The source of the idea was practical: if the architect's specification and the quantity surveyor's bill are divided into the same sections with the same titles, the contractor can find the same subject in the same place in both documents, and fewer things are missed or contradicted.

It came out of the industry's coordinated project information work, and it is now looked after by the Construction Project Information Committee (CPIC). CAWS was used to arrange the national building and engineering specifications of the period and the Standard Method of Measurement of Building Works, seventh edition (SMM7). That is why a generation of architects, surveyors and contractors learned the section letters as a shared language.

A second edition was published in 1998. Its main purpose was to align CAWS with the Unified Classification for the Construction Industry (Uniclass), published in 1997, in which a table of work sections for buildings reproduces the CAWS group, sub-group and work section headings. The 1998 edition defines more than 300 work sections.

What CAWS was designed to achieve

The authors set out four aims, which are still a fair summary of what a technical director wants from any arrangement: good coordination between drawings, specifications and bills of quantities; predictability of where a given piece of information will be found; fewer oversights and discrepancies between documents; and flexibility for the contractor to divide the project information into work packages.

The fourth aim explains much of CAWS's shape. Sections follow how work is let and priced, which is by trade and material. A bricklayer, a roofer and a plasterer each find their work under a recognisable letter. That was a deliberate decision, and it is the reason CAWS has lasted. It is also the reason it struggles when the question changes from "who builds this" to "what is this, and where does its data live".

How is CAWS structured, and what do the group letters mean?

CAWS groups work sections under letters A to Z (with I and O not used). Each section is a letter and two digits, for example F10 brick and block walling or M60 painting and clear finishing.

A CAWS reference has three levels. The group is a letter. The sub-group and work section are carried in the two digits that follow. A reference such as M60 therefore reads as group M (Surface finishes), and work section M60 within it, Painting and clear finishing. Clauses inside a section are normally cited with a slash and a clause number, so a drawing note or a cross-reference to the painting section reads as "M60/" followed by the clause reference. That slash convention is how a clause in one section points to another in a specification.

The letters run from A to Z with I and O left out,. The grouping follows the sequence of a building project. The front of the specification holds the contract and general conditions (A), then the whole building or unit (B), then work to existing fabric (C), groundwork (D), the structure and envelope (E to J), the internal linings and joinery (K and L), finishes and fittings (M and N), sundries, external works and the services groups (P to X), and finally the reference specifications for fabric (Z).

Sections are small enough to be let as work packages

The detail is where CAWS earns its keep. Group F does not just say masonry. It separates brick and block walling (F10), glass block walling (F11) and natural stone walling into their own sections. Group K separates plasterboard dry lining and partitions (K10) from suspended ceilings and raised floors. Group L puts windows, rooflights, screens and louvres (L10) apart from doors, shutters and hatches (L20). A site agent can lift a section out, price it and sublet it without disturbing the rest.

Two groups work differently from the rest. Group A holds the preliminaries and general conditions: project particulars (A10), tendering arrangements, quality standards, site facilities and similar. Group Z holds reference specifications for building fabric, so that purpose-made joinery, fixings, mortars and sealants can be specified once and referred to from the trade sections. Understanding how those two groups behave matters when a practice builds an office master, because they carry the clauses that every project inherits.

Practices extend the arrangement

Because the published list is finite and construction is not, practices and specification libraries add sections for newer materials and systems, and sometimes reuse a gap in the numbering. Two offices that both say they use CAWS may therefore have different numbers for the same subject. When you map CAWS to anything else, map your own master and not the published list.

How is CAWS used in specifications and bills of quantities?

A CAWS-numbered specification is arranged as one chapter per work section, and bills of quantities built on the same arrangement use the same headings. Drawings and schedules refer to the section number so the reader can find the requirement.

In a specification, CAWS gives you the table of contents. Each work section is a chapter: the practice's clauses for brickwork sit in F10, for plasterboard linings in K10, for windows in L10. The section carries the scope, the materials and products, the workmanship, the testing and the submissions for that package of work. The numbering lets a contractor scan the front sheet and see immediately which packages the project contains.

In a bill of quantities, the same headings arrange the measured items. SMM7 was built around the CAWS arrangement, which is the reason a bill and a specification written by different people could still be read side by side. Where a project uses a bill, the quantity surveyor can align each bill section with the specification section that governs the items in it, and a pricing query can be answered by pointing to one place.

How CAWS appears on the drawings

On the drawings, CAWS does most of its work through references. A note reading "refer to specification section M60" sends the reader to the finishes section. A drawing key may carry the work section beside a material hatch. A door or window schedule may include a column for the specification section that governs each type. None of that classifies the door itself. It only points to the chapter that describes the work, which is why schedules and specifications written under CAWS rely on people to keep the two in step.

Where CAWS-numbered specifications are built

Most practices that use CAWS do so through an office master, which is a library of preferred clauses arranged under CAWS section numbers. The master is the practical home of CAWS in a practice. If the master is well kept, the numbering stays consistent from project to project, and standard clause references (for example from a general section to a trade section) hold. If the master is not kept, section numbers drift and cross-references fail. The Office Master Specification: A Technical Director's Guide covers how to own and maintain one, and How to Keep an Office Master Specification Up to Date covers the review cycle.

The numbering also drives outputs outside the specification. A tender return from a subcontractor is often arranged by work section. A contractor's package plan, a cost plan and a submittal register commonly follow the same letters. That reach is the main reason a practice hesitates to leave CAWS: a change in the specification structure ripples into the documents the contractor builds on top of it.

What are the strengths and limits of CAWS?

CAWS is strong at arranging a specification by trade package and weak at identifying systems, products and model objects. It was built for documents read by people, and it stops where data has to be shared with software.

The strengths of CAWS are the strengths of a convention that everyone already knows. A technical director who says "K10" does not need to explain. The letters line up with trades, so a subcontractor reads the specification for their package and nothing else. A clause library built on CAWS is easy to keep tidy, because each subject has one obvious home. For a practice working mostly on domestic, small commercial and refurbishment projects with a conventional procurement route, none of that is a minor benefit.

The limits are about what CAWS leaves out

CAWS classifies work sections, and only that. It does not tell you what a wall build-up is, which products are in it, or which model objects represent it. A single external wall system might draw on masonry, insulation and membranes, windows and sealants, each in a different CAWS section. The specification is correct to split it, because the work is let in packages. The information about the wall as a whole system then has no home of its own, and nothing in CAWS lets the specification, the schedule and the model refer to the same object.

The arrangement also reflects the construction methods of the late twentieth century. Modern methods of construction, heat pump systems, whole-building certification and off-site manufactured components do not always fall neatly into a trade section. Practices cope by extending the list, and the extensions vary from office to office.

The last limit is the age of the source. The second edition dates from 1998. Practices that rely on CAWS are relying on a stable reference that is no longer developed in step with the industry. That is a reasonable description of a convention that has done its job, and it is also why information-management requirements have moved to Uniclass 2015.

How does CAWS relate to Uniclass 2015, and should your practice stay on it?

CAWS arranges work sections and Uniclass 2015 classifies systems, products and elements, so they answer different questions. Most practices keep CAWS for specification numbering and add Uniclass for model and schedule data, moving the master only when the work demands it.

CAWS and Uniclass 2015 are related by history rather than by design. In the 1997 Uniclass tables, a table for work sections for buildings reproduced the CAWS headings. Uniclass 2015 is a new set of tables with a different purpose. It classifies things (systems, products, elements, spaces, activities, roles) rather than packages of work. Uniclass 2015 is compliant with ISO 12006-2, and the UK BIM Framework guidance on ISO 19650 describes it as the preferred classification system in the UK. For a project run to ISO 19650, information containers and model data are expected to carry classification metadata, and in the UK that normally means Uniclass 2015. ISO 19650 for Architects sets out what that means in practice.

That is why practices move. The trigger is rarely the specification. It is a client's information requirements asking for Uniclass codes on model objects, a consultant team sharing a model, or a wish to use one set of identifiers across model, schedule and specification so that a change in one is visible in the others. Uniclass Codes Explained introduces the tables and code formats, and CAWS to Uniclass Mapping shows how work sections relate to systems and products.

A short test for staying or moving

The decision is practice-wide and has a cost, so put it as a set of questions and answer it from your own project list.

The usual answer is both

For most practices the realistic position is a hybrid. The specification keeps CAWS section numbers because the supply chain reads them and the office master is built on them. The model, schedules and product data carry Uniclass codes because clients and tools ask for them. A mapping holds the two together. That arrangement is stable provided the mapping has an owner, is reviewed on a cycle and is tested before each issue. A practice that decides to move the master itself will find a staged route in CAWS to Uniclass: Migrating an Office Master.

Stay on CAWS

Domestic and small commercial work, conventional procurement, no information requirements naming Uniclass, a master that is well owned.

Run both

Mixed project types, some clients requiring Uniclass, model data classified in Uniclass while specification numbering remains CAWS.

Move to Uniclass

Mostly BIM-led or public sector work, a master being rebuilt anyway, and a team ready to hold one classification across model, schedule and specification.

Questions technical directors ask about CAWS

What does CAWS stand for?

CAWS stands for the Common Arrangement of Work Sections. It is a UK classification of work sections for building work, used to arrange specifications and bills of quantities so that the same subject sits in the same place in every document. Sections carry a letter and two digits, such as F10 for brick and block walling.

When was CAWS first published, and is there a newer edition?

CAWS was first published in 1987. A second edition followed in 1998, aligning the arrangement with the Uniclass tables published in 1997. The 1998 edition is the one most practices still work from.

How many CAWS groups are there?

CAWS groups are identified by letters from A to Z, with I and O not used. They run from A (Preliminaries) and B (Complete buildings) through to Z (Building fabric reference specification). Each group divides into sub-groups and then into work sections.

Is CAWS the same as Uniclass?

No. CAWS arranges work sections, which are packages of work such as masonry or painting. Uniclass 2015 classifies systems, products, elements, spaces and other things in the built environment. The two answer different questions, so a specification can use CAWS for its section numbers while the model and schedules carry Uniclass codes.

Do I have to move from CAWS to Uniclass?

Not by default. CAWS still works for specification layout on projects where no client or information requirement asks for Uniclass. Practices tend to move when clients ask for Uniclass codes in the model and in information deliverables, when they work on BIM-led projects, or when they want one classification across model, schedule and specification.

Can a practice use CAWS and Uniclass together?

Yes, and many do. A common arrangement is to keep CAWS-numbered specification sections and add Uniclass codes to clauses, schedules and model objects, using a mapping to connect the two. The mapping needs an owner, because a work section often relates to several Uniclass systems and products.

Where Avoice fits

A CAWS-numbered specification is only as consistent as the master behind it. Avoice treats the master, the rules and the model link as one system, so the section numbers hold and the classification question does not force a rebuild.

Avoice specification output is CAWS-numbered, so a practice that works in CAWS keeps its section structure. The office master is a governed library with an owner, and projects draw from it instead of copying the last job. Practice rules (the values, standards and words the practice requires) are applied as the specification is written. The pre-issue Technical Review compares the specification against schedules and drawings, which catches the cross-reference and numbering faults that creep in when a CAWS master is not maintained.

For practices adding Uniclass, Avoice writes specifications in CAWS or Uniclass 2015: each clause carries a CAWS reference or a Uniclass code, and the practice chooses which. Avoice can map an existing CAWS master to Uniclass 2015 and flag the sections that need a decision, with the practice reviewing and approving each mapping. The BIM integration links clauses to Revit and ArchiCAD model objects, and Linking Uniclass Codes in Revit and ArchiCAD to Your Specification covers the classification set-up on the model side. The boundary is the usual one: software can retrieve, compare and flag, and the technical director still decides what the practice classifies by and when to move.