The Common Assessment Standard for construction suppliers

The Common Assessment Standard (CAS) is Build UK's shared prequalification question set and assessment standard for construction suppliers. It gives buyers a common way to ask about a supplier's organisational capability, while giving suppliers a route to certification through a recognised assessment body. It is a prequalification assessment, not a substitute for checking whether a firm, its people and its proposed method are suitable for a particular job.

This guide explains what the standard covers, how to prepare an evidence file and what a buyer should still check before appointing a contractor.

Who uses the standard?

Build UK maintains the CAS and lists the contractors and clients that accept it. Suppliers apply through a Recognised Assessment Body. Build UK says companies are certified annually and offers desktop and site-based certification levels. The appropriate level depends on the trade, business and client requirements. Check the buyer's procurement instructions before assuming a particular level will be accepted.

Assessment bodies are not interchangeable with the standard itself. Constructionline, CHAS, SMAS Worksafe and others can assess or display CAS certification, but a general membership tier or an SSIP health and safety certificate should not automatically be described as full CAS certification. Confirm the exact assessment product, level, scope and status with the issuing body.

For a guide to one provider rather than the common standard, see what Constructionline is. For the separate health and safety mutual-recognition mechanism, see what SSIP is.

What does the current question set cover?

Build UK's published Version 5 question set, dated 1 July 2025, contains ten sections: identity; financial standing; corporate and professional standing; health and safety; environmental management; quality; building safety; fairness, inclusion and respect; information security; and information management. The supporting questions and evidence differ by circumstance, so use the current question set and assessor instructions rather than an old generic PQQ checklist.

The building safety section matters particularly where a supplier is asked to show organisational capability for its role. Certification can organise that evidence; it does not certify a contractor as competent for every design or construction task. The Health and Safety Executive says the relevant skills, knowledge, experience and organisational capability should be proportionate to the work and its risks.

Build UK currently says Version 6 is scheduled for 1 November 2026. Before submitting, check which version the assessment body is using and whether a transition period applies. Do not rely on this article as a fixed list of required documents after the question set changes.

A practical supplier preparation sequence

1. Identify the work and buyer requirement. Write down the trade, intended role, sites and any requested desktop or site-based level. Ask whether the buyer requires CAS certification or a different approval in addition.
2. Confirm the assessment route. Choose a body from Build UK's current recognised list. Check its CAS product, submission process, assessment level and renewal terms directly with that body; avoid assuming that an existing membership automatically includes CAS.
3. Assign an owner to each question-set section. Finance, HR, safety, quality and IT evidence often sit with different people. An owner should confirm the document is current and actually answers the question.
4. Check scope and dates before upload. A company name, policy, insurance certificate or accreditation can look plausible while belonging to the wrong entity, covering the wrong activity or having expired. Review the underlying document, not merely a register entry.
5. Resolve gaps honestly. If a control or record does not exist, create the real process and evidence before declaring it complete. Do not backdate a policy, training record or inspection.
6. Review the submitted version. Record what was sent, to which assessment body, under which question-set version and who approved the response. Keep a route for updating time-sensitive evidence between annual assessments.

A useful working register has columns for section, question, evidence file, legal entity, relevant scope, owner, effective date, expiry or review date, assessor query and final status. The register is an operational aid; it is not proof that the underlying control works.

What should buyers check beyond the certificate?

A buyer can use CAS to reduce repeated organisation-level prequalification questions. The project still needs a task-specific decision. At minimum, confirm:

• the certification belongs to the entity bidding or being appointed;
• its current status, level and relevant scope with the recognised assessment body;
• the actual people, qualifications and supervision proposed for the work;
• site hazards, interfaces, risk assessment and method statement for the particular job;
• relevant insurance terms, licences or statutory registrations where applicable; and
• how changes, subcontracting and expired evidence will be managed during delivery.

This distinction follows the HSE's contractor guidance: selecting a suitable contractor, assessing the risks, providing information and managing the work are connected but separate steps. A CAS certificate cannot replace the client's and contractor's work-specific duties.

Does CAS replace PAS 91 or SSIP?

CAS is the current Build UK framework to use for a CAS assessment. Older PAS 91-based questionnaires may still appear in archived templates or a buyer's process, so check the actual tender instructions instead of assuming every buyer has migrated. If a buyer asks for PAS 91 evidence, clarify whether it will accept a current CAS assessment and which additional questions it needs.

SSIP has a narrower function: its member schemes assess against shared health and safety core criteria and may mutually recognise an existing assessment through “Deem to Satisfy.” That does not establish that the supplier has completed all ten CAS sections. Conversely, a supplier holding CAS should check its assessment body's exact SSIP status rather than describing every CAS certificate as equivalent to every scheme registration.

Where software fits

The administrative challenge is maintaining evidence across owners and assessment cycles. A contractor prequalification software evaluation should test whether the product can hold the actual documents, identify their owner and expiry, show what has changed since submission, and make it easy to prepare the evidence a buyer or assessor requests. Ask the vendor to demonstrate each function with your own document types. Software organises evidence; Build UK and its recognised assessment bodies decide CAS criteria and certification.

Sources and claim boundaries

• Build UK — Common Assessment Standard: owner of the standard; assessment levels, recognised bodies, annual certification, current Version 5 and scheduled Version 6.
• Build UK — Version 5 question set: section names and dated question-set version.
• HSE — Are you a contractor?: proportionate skills, knowledge, experience and organisational capability under CDM 2015.
• HSE — Using contractors: contractor selection, risk assessment, information and supervision as separate responsibilities.
• SSIP — Deem to Satisfy: scope and limits of mutual recognition.

Editorial note: The CAS version and recognised body list are time-sensitive. Recheck both immediately before integration or publication. No Complys certification, automatic approval, pricing or trial claim is made here.