When developing any product, it is the practice that designs are developed with the required details showing how all constituent parts will be assembled to form it.
Together with these details, a text-based document is essential to describe all other aspects of assembling these parts that cannot be adequately captured in a graphical form in the drawings. This is called a specification.
The construction industry works the same. The building is the product. Drawings, details, and other contract documents are produced to describe the building and the assemblage of its parts. A construction specification is then written to provide further details on the steps, requirements, and all that pertains to helping clearly define the scope of the work to be done by the builder on-site.
Introduction to Specifications
Specification is a term applying to all directions, provisions, and requirements for the performance of works.
Also, it is a term generally defining the requirements for products, materials, processes, and workmanship on which a contract is based, and the requirements for the administration, monitoring and performance of a project.
It can also be defined as the skill of recording specific requirements for work you or your client wants to be done.
Therefore, a construction specification is a well-structured, detailed description of the quality, standards, workmanship, materials, and completion of work to be done, which evolves across a project.
Specifications are often prepared by architects, engineers, quantity surveyors, project managers, and designers, referred to as specifiers and may be published as part of the contractual documentation for contractors to be read in parallel with models and drawings, as part of the handover information.
This information can be captured at any stage of the design process before actual construction starts on-site. Early client requirements and building performance requirements should be recorded and will develop over time into choices about the systems and products needed, and descriptions of their performance against standards, key properties, and manufacturers.
A well-written specification is vital for everyone working on a construction project, as it sets out every detail of the products and processes that will be used. It will help prevent delays, cost overruns, and disputes, which negatively impact the success of a project.
Specifications are one of the basic components that comprise a contract agreement between the project owner (the client) and the contractor.
Types of Specifications
Different types of specifications can be used at the various stages of a project’s development.
At an early stage, requests from the client, in the form of a client brief and high-level design ideas, can be captured as an outline description, then the requirements of the building, systems and products can be specified in performance terms in a descriptive or performance specification, such as acoustic, thermal, or structural requirements, and the specification further developed into more prescriptive clauses selecting the standards, grades and materials of component products.
Proprietary specifications include product information like range names, reference codes, and key properties selected from manufacturer choices. This specification is often developed in tandem with project preliminaries, managing the contractual and project-wide requirements and will continue to evolve as changes are requested, eventually forming the project handover data that will be passed over to the facilities management phase of the project.
The following are the main types of specifications described according to their specific uses:
Descriptive Specifications
This entails a detailed written description of the required properties of a product, material or piece of equipment and the workmanship required for its proper installation.
It is also known as prescriptive specifications and provides details on the types of materials and installations needed to complete a project.
Additionally, they describe how to measure installations to ensure they are up to project quality and standards.
Performance Specifications
This is a statement of required results with criteria for verifying compliance, but without unnecessary limitation on the methods for achieving the results, or it can be defined as specifying an end result by formulating the criteria for its accomplishment.
A performance specification is a document that describes the operational requirements when work is completed or a product is installed.
They should describe to the contractors what is needed for the final product and how it should function once completed.
Reference Standard Specifications
These are requirements set by authority, custom or consensus and are established as accepted criteria, such as British Standards, Eurocodes, and KEBS (Kenya Bureau of Standards).
Proprietary Specifications
These types identify the desired products by manufacturer’s name, brand name, model number, type designation or other unique characteristics.
This method can be open or closed depending on whether substitutions are permitted.
It is mainly used when only one product can be used for an installation, especially when equipment or machinery requires only one certain material that indicates performance.
Purpose of Construction Specifications
The following are some of the purposes of specifications in a construction project:
- To guide the bidder at the time of tendering to arrive at a reasonable cost for the work.
- To guide the execution and supervision of works.
- To guide the contractor for the purchase of materials.
- To guide the bidder to identify and evaluate his capacity to execute the works.
- To serve as a fabrication and installation guide.
- Helps the manufacturers of construction materials, equipment, tools, etc. to grade, classify and improve the qualities of their products.
- Indirectly, the specifications are very much related to the legal considerations, insurance considerations, bidding requirements, alternatives and options, obligations and remedial measures for the contracting parties.
- In the event of conflicts between specifications and drawings, the specifications govern.
Information to Include in a Specification
The specification information describes, in words, things that cannot be visualised or explained in drawings and the virtual building model.
The content can include site requirements, contract information, client requests, performance criteria to be achieved, the quality of products required, references to various standards applicable to the materials and systems selected, the method of work completion and testing, and maintenance of the building during use.
Some dimensions, for example, tolerances or coating thicknesses, may be specified, but the specification is not the best place for visual information like more complex dimensions, positions, and geometry, or lists of schedules and quantities, which should be captured in the model and drawings instead to allow for more accurate pricing and cost information.
The 3D model and drawings cannot replace the specification, as some items will never be modelled, and performance, standards, and execution requirements are not captured. Notes on the drawing outputs are not a replacement for a well-written specification.
Some information in a construction specification includes the scope of work, materials, a timeline with milestones, methods of installation of components, quality of workmanship, testing requirements, and safety standards.
Sources of Specification Information
We identified the following sources of specification information:
- Contract drawings: drawings prepared in the initial stages of the project contain useful details that can inform the development of specifications.
- Previous specifications: for a completed or ongoing project.
- Owner requirements: these are captured from the client’s brief during the briefing stage, through the employer information requirements.
- Site Investigation: this will reveal existing site conditions that may be useful in specifying clearance works, soil excavation, etc.
- Standard Specifications: references can be made to the relevant standard specifications.
- Product catalogues: manufacturers, distributors, suppliers, etc., share catalogues for their products with technical information that is useful in drafting specifications.
Principles of Writing Good Specifications
The following seven key principles need to be adhered to for the specifiers to write and produce good specifications:
- Clear (Clarity): Use clear, plain language and short phrases to list requirements. Avoid ambiguity to improve understanding for all users.
- Concise: Don’t include information that isn’t required or relevant – make the specification project-specific.
- Correct: Clarify requirements, refer to outcomes, and reference current building standards and building codes wherever possible.
- Complete: Ensure the depth of information is appropriate. Only address the contractor; don’t specify differently for subcontractors or manufacturers.
- Comprehensive: Ensure all aspects of the project are covered – “say it once, in the right place” and use cross-references to avoid repetition or conflicts.
- Consistent: Use standard structure, terminology, and style. Keep outputs neat when published, so they are easy to navigate and understand for all receivers.
- Co-ordinated: Ensure that drawing references in the specification are kept up-to-date to match model annotations and other contract documentation.
Conclusion
We hope this general discussion on construction specifications has been helpful to you. If there’s anything you need clarified, please raise the questions in the comments section below.