16 January 2019
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1. Background

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

The content in NBS Building is arranged by CAWS, so to write a specification for an external window, the user would add the work section L10, ‘Windows / rooflights / screens / louvres’ to their project.

The content in NBS Chorus is arranged by Uniclass 2015, so 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 this. However, CAWS is no longer maintained as a classification system, and more clients are requiring Uniclass 2015.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, consider the following benefits of Uniclass 2015.

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 main difference here is the specifier’s ability to consider all of the potential products by using the system outline clause to ensure that none are missed. 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 Building
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.

2.2 A home for performance content

When updating the Plan of Work 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, it is likely that there will be a requirement to specify certain systems by their overall performance.

When following a CAWS-based specification, there is no location for this performance content. For example, there would 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 clauses specifying the desired structural, fire, durability, health and hygiene performance may be added from the system outline clause when structuring by Uniclass 2015. The rules for design submittals and compliance may also be specified with these performance requirements.

This provides clarity to the Contractor 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 a systems-based structure is that is also provides a home for ‘system completion’. Therefore, any specification requirements for cleaning, submittals, spares, training and defect period 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 specified in the same work section. Figure 2.3.1 illustrates an example of this in NBS Building.

This creates a challenge if these systems have different design responsibilities, 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 and the plastic windows. There are also separate specifications for the louvre and brise soleil systems that are part of a contractor design portion of the work.

Furthermore, with respect to packaging, this allows for a greater granularity in the situation where different trades work on these different parts of the building.

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. 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 standards ISO 19650, Parts 1 and 2 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, BS EN ISO 19650, lists Uniclass 2015 as the required classification system for work in the UK (see Figure 3.1.1).

If, as expected, clients and project teams will insist that all information developed on a construction project is to ISO 19650 then all disciplines will move to using a Uniclass 2015-based specification system.

Figure 3.1.1: ISO 19650 and Uniclass 2015

Figure 3.1.2 shows an example of Uniclass 2015 annotations displayed on a drawing generated from a model. The annotations for the systems and products help coordinate the documentation set of drawings and specification. Codes for items such as spaces, activities and entities allow for further cross-referencing to the wider documentation set.

Figure 3.1.2: 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: