Output-based specifications define the client's functional requirements for the proposed development.
The output-based specification is particularly important on public projects as the government preferred procurement routes (design and build, prime contract and private finance initiative) all involve appointing an integrated supply team (including designers, contractors and suppliers) under a single contract to design and construct (and sometimes to finance, operate and maintain) the development.
The integrated supply team is appointed with no design information, but with just the output-based specification to set out the client's requirements. Once the integrated supply team has been appointed, the client may find that changing their requirements can prove expensive. See Government Construction Strategy for more information.
The output-based specification may be a development of the project brief, but it is separate from it as it defines only the outputs that are required from the project (that is, what it will enable the client to do), it does not attempt to address how those outputs might be achieved.
It is considered by government that this will get best value from the integrated supply team by allowing them to adopt innovative solutions to the client's requirements and reducing whole-life costs rather than simply developing the client's pre-conceived solutions.
For example, an output based specification might require the provision of a classroom for 30 primary pupils, but it would not specify the nature of the classroom, the types of doors and windows etc. The standard of the classroom to be created might be defined by reference to existing guidelines. As many of the building types procured as publicly-funded projects are of a standard type (schools, hospitals, prisons etc.) there are a great number of standards and guidelines setting out performance requirements.
The Common Minimum Standards (CMS) set out some very broad standards to which built environments procured by government departments need to comply. Adoption of the Common Minimum Standards is mandatory in central government departments in England.
Output-based specifications must be well developed and concise otherwise the quality and performance of the completed development may be compromised.
An output-based specification might include:
- Introduction (purpose of the document).
- Business objectives.
- Business functions and processes.
- The functions the development is required to perform.
- The scope of services to be provided.
- The number and type of users the development will serve.
- A description of stakeholders.
- An organisational structure showing the relationship between client functions.
- Indicative equipment schedules.
- Constraints on the nature of the development, such as limitations of the site, interaction with other organisations etc.
- Sustainable performance objectives.
- Specific services requirements such as information technology requirements.
- Access requirements.
- Environmental requirements.
- Existing policies.
- Quality standards.
As public projects can be procured on a design, build and operate basis, it is important that the output-based specification includes requirements to allow the development to be upgraded and altered through its life.
 Related articles on Designing Buildings Wiki
- Briefing documents.
- Feasibility studies.
- Preliminary business case.
- Project brief.
- Project execution plan.
- Statement of need.
- Common minimum standards.
- Government construction strategy.
- Insulation specification.
- Major Projects Authority.
- Outline specification.
- Performance specification.
- Procurement route.
- Public procurement.
- Service level specification.
- Specification basics.
- Strategic brief.
- User panels.
- Tender documentation.
 External references
- OGC Expected outputs and outcomes (output based specification).
- OGC Achieving Excellence Guide 3 - Project Procurement Lifecycle.
- OGC Achieving Excellence Guide 6 - Procurement and Contract Strategies.
- OGC Achieving Excellence Guide 7 - Whole-Life costing.
- OGC Achieving Excellence Guide 9 - Design Quality.
- OGC Achieving Excellence Guide 11 - Sustainability.
- Common Minimum Standards.
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