16 October 2019

One of the questions most commonly asked of NBS is what the differences are between structuring specifications by Common Arrangement of Work Sections (CAWS) and Uniclass 2015.

Update (3rd Jan 2024) - This article was written in Oct 2019. Since then Uniclass 2015 has had its name simplified to Uniclass and more information on Uniclass can be found at https://www.thenbs.com/uniclass - In addition, although CAWS as a classification system (as part of Uniclass 1.4) is no longer maintained, the NBS specification libraries in CAWS structure are being actively developed and maintained in line with industry demand. Sample specifications in CAWS and Uniclass format can be downloaded at https://www.thenbs.com/nbs-sample-specification

1. Background

One of the questions most commonly asked of NBS is what the differences are between structuring specifications by Common Arrangement of Work Sections (CAWS) and Uniclass 2015. CAWS is in fact Table J from the old Uniclass 1.4 system. The NBS Chorus specification platform allows construction professionals to write specifications in the structure and classification of their choosing.

When writing a specification in CAWS format for an external window, the user would start by adding the work section L10, ‘Windows/ rooflights/ screens/ louvres’ to their project.
When using Uniclass 2015 to write a specification for an external window, the user would add the specific system from Ss_25_30_95, ‘Window systems’.
The industry has used CAWS for many years, and is familiar with it. However, CAWS is no longer maintained as a classification system, as it is from an earlier version of Uniclass, and more and more projects are now selecting Uniclass 2015. This article from NBS Innovation Director Dr. Stephen Hamil looks at the reasons why Uniclass 2015 is preferable to CAWS in many cases.

2. Considerations

When facing the choice between organizing specifications on a project by CAWS or Uniclass 2015, the following benefits of Uniclass 2015 should be taken into consideration.

2.1 Associate all Construction Products with their Parent System.

In Figure 2.1.1 below, a board-suspended ceiling system is being specified in CAWS format. By looking at the scope statement, it can be seen that products such as plasterboard linings and dry lining jointing are covered in the work section K10. However, products to cover the framing, the insulation and the fire stopping are covered in other work sections (G10, P10 and P12, respectively).

In Figure 2.1.2, a board-suspended ceiling system is being specified in Uniclass 2015 format. The clear difference here is the specifier’s ability to consider all of the potential products by using the system outline clause to ensure that no product is overlooked. In this example, the grid, the fasteners, the insulation and the ceiling void barriers, etc., are all being added to the job as part of the ceiling system specification process.

Figure 2.1.1: Specification content structured by CAWS in NBS Chorus
Figure 2.1.2: Specification content structured by Uniclass 2015 in NBS Chorus

With respect to those receiving a specification in Uniclass 2015 format, they can understand the construction of the specific ceiling system without having to jump between cross references to a number of different work sections. All of the information can be found in one place, without having to search through several work sections to find it.

2.2 A home for performance content

When the Plan of Work was updated in 2013, research from the Royal Institute of British Architects indicated that around 40% of architects frequently work on design and build projects. NBS research across the wider industry in 2018 found that, for 41% of organizations, design and build was the most frequent method of procurement.

Whether you are working on traditional projects with contractor design portions or full design and build projects, there will be a requirement to specify certain parts of the work by their overall performance.

When following a CAWS-based specification, there is no natural location for this performance content. For example, there could be uncertainty over whether a ceiling system’s overall performance should be specified in the work section for the lining, the frame, the insulation or the fire barriers.

Figure 2.2.1 below shows that when structured by Uniclass 2015, clauses specifying the desired structural, fire, durability, and health and hygiene performance may be added from the system outline clause. The rules for design submittals and evidence of compliance may also be specified with these performance requirements.

This provides clarity to all parties over what the design criteria are, and how they will be tested.

Figure 2.2.1: Links to clauses that specify the performance of the system to inform contractor design

An additional advantage of this structure is that is also provides a home for ‘system completion’. Therefore, any specification requirements for cleaning, submittals, spares, training or maintenance can be added.

2.3 A finer granularity for packaging

Within a specification structured by CAWS, the granularity can often be quite broad. For example, if a project requires different types of windows, rooflights, louvres and brise soleil systems then the main components are often specified in the same work section. Figure 2.3.1 illustrates an example of this with CAWS content in NBS Chorus.

This creates a challenge if these systems have different levels of contractor design, and further challenges if this specification content is required to be split between different work packages.

Figure 2.3.1: The scope of L10 in NBS Building covers many aspects of the design

Figure 2.3.2 shows how by using a systems-based classification system, such as Uniclass 2015, it is possible to have separate specifications for the distinct system types.

In this example, there is a specification for both the wood windows and the plastic windows. There are also separate specifications for the louvre and brise soleil systems that are included in a ‘contractor design’ part of the work.

Furthermore, with respect to packaging, this allows for a greater granularity in a situation where different sub-contractors work on these different parts of the building – for example, one sub-contractor working on the plastic windows and rooflights and another on the wood windows.

Figure 2.3.2: Splitting the specification into distinct systems makes it easier to package in order to identify both design responsibility and work packages

3. Contract preliminaries

As for contract preliminaries, the software experience is identical whether CAWS or Uniclass 2015 is used. However, the clauses are grouped together in different sections. Figure 3.1 below shows the more traditional ‘A10, A11, A12’ section structure. Figure 3.2 shows this same content structured using the Uniclass 2015 Project Management codes. In CAWS, Preliminaries are ordered according to whom the information is intended for, while in Uniclass 2015 it is ordered to follow the project timeline. The broad effect is the same – the principal difference being that in NBS Building users need to choose a contract before being given access to all the content, whereas NBS Chorus allows users to complete some parts of the Preliminaries without first having to choose a contract.
Figure 3.1: Contract preliminaries in CAWS format
Figure 3.1: Contract preliminaries in Uniclass 2015 format

4. Information management standards

In addition to these specification examples, there is also the need to consider how the specification fits into the wider information set that is developed as part of any construction project.

The international ISO 19650 series of standards outline how to organize information on a construction project. These standards detail the requirement to use a classification system that follows the ISO 12006-2 framework, such as Uniclass 2015. The UK National Annex to BS EN ISO 19650-2 lists Uniclass 2015 as the required classification system for work in the UK (see Figure 4.1).

Therefore, it is likely that Uniclass 2015 will become the classification of choice for clients and design teams, and this will be mandated for other members of the project team.

Figure 4.1: ISO 19650 and Uniclass 2015
Figure 4.2 shows an example of Uniclass 2015 annotations displayed on a drawing generated from a model. The annotations for the systems and products help to coordinate the set of drawings and specifications. Codes for items such as spaces, activities and entities allow for further cross-referencing to the wider information set.
Figure 4.2: A single classification for the built environment

Examples of using Uniclass 2015 codes for the analysis of government assets may be viewed in the Centre for Digital Built Britain publications below:

Further reading: