Design freeze

An important gateway in the design/procure/build process

Executive summary

Change during construction can be expensive and time-consuming. To avoid this, there must be a point in an engineering-procurement-construction (EPC) project or any other design activity when a formal stop is placed on the evolution of the design. This point is known as ‘design freeze’ and marks the end of the formal design effort – or, at least, that is the intention. It forwards a constructible design that can be built on site with no further changes. A preliminary stage to design freeze is ‘design chill’ where the design organisation starts to take formal control over change. It is good practice for design chill and design freeze to take place simultaneously at review points that permit continuation of the works. These are commonly known as ‘gates’. This article explores the gates process as it relates to design chill and design freeze. In terms of the PDCA cycle, this falls under the heading of ‘check’. Once the design has been frozen, it should enter formal change control (see the article ‘Change control’).

The gates process

A gate is a formal review of the status of a project with a view to permitting its continuation. Too commonly, sparse attention is paid to gates with the result that incorrect and incomplete designs are issued for construction. It is essential that a thorough review be undertaken before freezing the design.

The most fruitful review will not only examine the completeness of the design to meet the client’s requirements, but will also involve the following:

  • A financial review to confirm that costs have run to budget to date and that future costs are properly forecast
  • A programme review to confirm that the project has completed all the steps needed to date on time and that any delays have been agreed and accepted by the client
  • All records, including design certification, have been completed and signed off
  • All requirements for entering into the next stage of the project have been met, including those required by the local authority, health and safety authorities and local residents
  • All documents needed for the next phase are readily retrievable and accurate to requirements.

In other words, the project is ready to move to the next phase, a decision supported by the senior management team. Failure of one element could be sufficient to fail the gate; for example, one missing signature on a design check certificate.

Design chill

At design chill, all aspects of the design may evolve, although formal controls are placed on any changes to issued design documents. This might mean that interim change may occur within particular aspect of the works, which, when finalised, are formally reviewed and incorporated into the design. This is also known as a “part freeze”.

Design chill also has the effect of reducing possible diversions into development that over-engineers the design or introduces additional “benefits” that were not foreseen at the start of the work.

Parts of a design can be chilled whilst permitting other aspects to continue to develop; for example, the civil aspects may be chilled, allowing M&E design to continue in the full knowledge that there will be no change to the structure.

Design freeze

The aim of a design freeze is to depict a single point in the EPC process where development ceases and the full set of design documentation can no longer be changed. This is intended to ensure that a robust design is provided to construction that can be constructed in full trust that all aspects have been properly designed.

Design freeze can occur at various points in the design process. Typically, these include:

  • Specification freeze that freezes the client’s requirements in a requirements definition document
  • Concept freeze that occurs once the conceptual design has been reviewed and has been accepted by the client
  • Detailed design freeze that permits release of the design to construction

However, the most common form of design freeze occurs at this last point, namely, the formal issue of the technical documents for construction.

Why freeze?

All forms of change are risky, costly and almost certainly impact on schedule. Change can also result in the client’s requirements not being met unless great care is taken during the change management process to review the end result of the change against the frozen specification. Freezing the design provides a level of assurance that it will meet the specification when constructed without interference from change. It also puts pressure on the designer to get it right first time, rather than doing 80% of the design and hoping that the rest will be picked up by construction as changes – especially if the contract makes the design organisation responsible for the changes!

Document control

Document control, or more correctly, information management, has a vital part to play in the way in which technical information is passed from one organisation to another. ISO 9001 requires that, in simplistic terms, the people who need information have the documents that they need at the pertinent revision. If they have the wrong documents, they will build it wrong – obviously. It is important that information management have proper control over all technical information once it has been formally placed under control. This means that they must be provided with the relevant documentation and that they alone hold responsibility for its issue under control. It should never be part of any organisation’s way of working to provide updates to construction ‘under the counter’, but always formally.


Original article written by Keith Hamlyn, reviewed by Tony Hoyle on behalf of the CQI Construction Special Interest Group, and accepted for publication by the Competency Working Group on 7 March 2018.

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