The Common Assessment Standard (CAS) is a single, industry-agreed question set that a small contractor answers once and can then use to satisfy pre-qualification requests from multiple main contractors, instead of filling out a different form for every client. It was developed by Build UK, and certification against it is carried out by one of seven Recognised Assessment Bodies — CHAS being one of them. CHAS's current product for this is called CHAS Elite (CAS) at desktop level, or CHAS Elite (CAS) Assured if you need the site-based version. Knowing which level a main contractor actually needs, and what the question set covers, is most of the preparation work.
Why CAS exists: one standard instead of many
CAS comprises an industry-agreed question set and corresponding assessment standards for pre-qualifying suppliers, built specifically to replace the multiple, repetitive and time-consuming pre-qualification processes that used to sit in front of construction contractors. Before it existed, a growing number of separate pre-qualification schemes was estimated to be costing the construction industry around £1 billion a year in duplicated effort. Build UK developed the standard together with the Civil Engineering Contractors Association and other accreditation bodies and industry experts, launching it initially in 2019.
The practical payoff is that certification is now accepted by a growing list of contractors and clients who no longer specify a particular assessment body by name — they'll take a CAS certificate from whichever Recognised Assessment Body issued it. A 2021 data-sharing agreement between the bodies accelerated that: once you're certified, your details can in principle be accessed via any of the providers, not just the one that actually audited you.
CAS has also effectively replaced its own predecessor. PAS 91, the standardised pre-qualification questionnaire that came before it, was withdrawn by the British Standards Institution in 2023 and is no longer being updated. And CAS now carries real weight in public procurement: under PPN 03/24, it's the government's preferred pre-qualification method for public sector construction projects exceeding £5.337 million.
Who can actually certify you
There are seven Recognised Assessment Bodies that can certify a company to the Common Assessment Standard: Achilles, Compliance Chain, Constructionline, CQMS, SCCS, Smas Worksafe, and Veriforce CHAS. All of them have demonstrated their capability to audit companies against the standard, so a certificate from any one of the seven should, in theory, be treated the same way by a main contractor. In practice, Constructionline handles the bulk of it — over 80% of all UK suppliers get their CAS accreditation through Constructionline, which is worth knowing if you're choosing between bodies rather than being told which one to use.
If a client wants your CAS status confirmed through a different Recognised Assessment Body from the one that actually certified you, that's a two-step administrative job, not a one-click lookup. You need to complete the receiving body's own data sharing form, and separately send an email to the Recognised Assessment Body that originally certified you, giving it permission to share your data. Skip the second step and the sharing request typically won't go through — worth doing well before a deadline, not the day a client asks.
What the question set actually covers
The current version of the standard — Version 5, published 1 July 2025 — organises everything into 10 numbered sections: Identity, Financial, Corporate and Professional Standing, Health and Safety, Environmental, Quality, Building Safety, Fairness, Inclusion and Respect (FIR), Information Security, and Information Management. Some older pages still list 13 areas; the current set has 10 sections.
Within those 10 sections, most questions are mandatory — fail to complete one properly and you won't get certified. A smaller number are marked as advisory: you don't have to complete them to be certified, though leaving them blank may show up when your verified data is shared with contractors and clients later.
Section 1, Identity, asks you to self-declare whether your company is a micro, small or medium-sized enterprise, and to give figures for total direct (PAYE) employees and total indirect personnel over the last 12 months. Section 2, Financial, asks for copies of your company accounts for the last two years, with different specific requirements depending on whether you're a small company or LLP, a medium or large incorporated entity, or an unincorporated business — so what you're actually asked to produce here depends on your company's own structure and size, not a single fixed list.
Exemptions worth claiming before you start
This is the part of CAS most small contractors underuse. You can be exempt from answering certain questions if you already hold other third-party audited certifications, or if a question genuinely isn't relevant to your business — if you don't employ sub-contractors, for instance, the sub-contractor management questions don't apply to you. The specific certifications that trigger exemptions include ISO 9001, ISO 14001 or EMAS, ISO 27001 or Cyber Essentials Plus, ISO 45001 or SSIP, BS 99001, and ISO 19650-2 — holding any of these can remove an entire block of questions rather than just one.
Separately, if you already hold CHAS, Constructionline or Achilles certification at a specific level — CHAS Elite, for example — that confirms you already meet CAS's requirements for certain sections, and you'd normally claim that through a data request form rather than answering the same ground twice. If you're already accredited somewhere and are now being asked for CAS specifically, check what you already hold before you start filling anything in from scratch.
Smaller firms get one more piece of proportionality built in. If your company employs fewer than 10 people and has a turnover below £1.8 million or a balance sheet total under £1.8 million, the assessment standards for certain questions are applied in a proportionate way — recognising that a two-person contracting outfit shouldn't need the same formal policy documentation as a 200-person firm. You can still choose to answer to the full standard if you'd rather, but you're not required to.
The Building Safety section: what changed in 2025
One section deserves its own mention because the rules around it moved recently. The Building Safety section became mandatory in the 1 July 2025 update for any company carrying out design or building work under the Building Safety Act, or working on Higher-Risk Buildings. It had actually been introduced back in July 2024 as an advisory section only, specifically to give the industry twelve months to get up to speed with the new requirements before it started counting toward certification. If you do that kind of work, this section is no longer optional.
One sector has been given more breathing room. Build UK has issued a statement allowing scaffolding and temporary works suppliers extra time to complete the Building Safety section, running until Version 6 of the standard is published on 1 November 2026. If that's your trade, check the current position with your Recognised Assessment Body rather than assuming the general July 2025 deadline applies to you in full.
Desktop versus site-based: what's actually different
CAS certification comes in two levels, and the difference is genuinely about how it's verified, not just a pricing tier. A desktop audit means the Recognised Assessment Body verifies the information you've submitted against the relevant assessment standard remotely, working from the documents you've provided. A site-based audit goes further: an auditor from the Recognised Assessment Body actually visits your premises to check that the policies and procedures you've described are being implemented in practice, not just written down.
Which level you need depends on your trade, your size, and what your clients are actually asking for — you apply to your chosen Recognised Assessment Body for the level that's appropriate to your business, not a fixed level everyone gets by default. Once you're certified, the certificate is valid for 12 months from the date of issue, provided you keep any "time-critical" documents — things like insurance certificates or specific policy documents with their own expiry dates — updated as they expire. Constructionline says its own audit process, whether desktop or site-based, can be completed in as little as three working days once you're ready to go, which gives you a rough sense of how much of the timeline is actually the audit itself versus your own preparation beforehand.
How CHAS's own levels map onto CAS
This is where a lot of confusion creeps in, because CHAS's branding has changed and older CHAS material doesn't use the current product names. Build UK's own official table of Recognised Assessment Bodies lists Veriforce CHAS's desktop-level product as CHAS Elite (CAS), and its site-based product as CHAS Elite (CAS) Assured — the same pairing is independently repeated in FIS's own listing of Recognised Assessment Bodies. Those are the current, official product names to look for.
For comparison, since it's a question worth asking if you're choosing between assessment bodies: Constructionline's Gold membership level aligns with desktop-level CAS certification, and its Platinum level aligns with site-based CAS certification, including a visit to your premises. Our own comparison of CHAS, SafeContractor and Constructionline goes into more detail on choosing between the assessment bodies themselves.
Preparing for the audit
Build UK publishes its own guide to the current question set specifically to help companies prepare for an audit by a Recognised Assessment Body — reading that guide alongside the actual question set is a reasonable starting point before you touch an application. Beyond that, the practical advice from bid specialists is straightforward: review the question set properly as part of your planning, work out which questions need a written narrative answer versus a simple document upload, and apply for any exemptions you're entitled to — via the relevant data request form — well before your deadline rather than at the last minute. If you're answering narrative questions properly the first time, save those responses; you'll likely reuse most of them for the next client that asks.
Once you're certified, the job isn't finished. You're required to keep time-critical documents updated as they expire to maintain your certification, and you may need to upload supporting documents for particular questions as part of that ongoing maintenance — a lapsed insurance certificate sitting behind an otherwise valid certification is exactly the kind of thing that trips contractors up months after they thought the process was done.
More than 21,000 suppliers are now certified to CAS.
Frequently Asked Questions
Do I need CAS if I already have CHAS? It depends on your CHAS level. If you hold CHAS Elite (CAS) or CHAS Elite (CAS) Assured specifically, you already hold CAS certification at desktop or site-based level respectively. Other CHAS membership levels may not automatically confirm CAS — check with CHAS or ask about a data request form before assuming you're covered. Our note on CHAS membership levels explained breaks down where each level sits.
What's the actual difference between desktop and site-based certification? Desktop means the Recognised Assessment Body checks your submitted documents remotely. Site-based means an auditor physically visits your premises to confirm what you've described is actually happening in practice, not just written down in a policy document.
Is the Building Safety section mandatory for us? It's been mandatory since 1 July 2025 for any company doing design or building work under the Building Safety Act, or working on Higher-Risk Buildings. Scaffolding and temporary works suppliers have been given extra time, running until Version 6 of the standard is published on 1 November 2026.
How long does a CAS certificate last? Twelve months from the date of issue, provided any time-critical documents — insurance certificates and similar — are kept updated as they expire in the meantime.
Can I skip questions if I already hold other certifications? Yes. Holding ISO 9001, ISO 14001/EMAS, ISO 27001/Cyber Essentials Plus, ISO 45001/SSIP, BS 99001 or ISO 19650-2 can exempt you from whole blocks of questions, and certain existing CHAS, Constructionline or Achilles certifications can do the same for specific CAS sections — check what you already hold before answering everything from scratch.
Deplexify can get you CHAS-certified: start with a free readiness check, then have the CHAS Submission Pack documents built for you from £149 in one working day, or have the whole application handled from £295. Those prices are for CHAS Standard; Advanced and Elite are priced on the plans page. More on our CHAS service.
Sources
- Common Assessment Standard - Build UK — builduk.org, read 2026-09-24
- Common Assessment Standard | Construction PQQ - Constructionline — constructionline.co.uk, read 2026-09-24
- The common assessment standard - Designing Buildings — designingbuildings.co.uk, read 2026-09-24
- What Is the Common Assessment Standard? | CHAS — chas.co.uk, read 2026-09-24
- Pre-Qualification and the Common Assessment Standard - FIS — thefis.org, read 2026-09-24
- PAS 91 vs Common Assessment Standard (CAS) Explained — liaisonsystems.com, read 2026-09-24
- Common Assessment Standard updated with mandatory building safety questions - Designing Buildings — designingbuildings.co.uk, read 2026-09-24
- What is the Common Assessment Standard? | Executive Compass — executivecompass.co.uk, read 2026-09-24
- Common-Assessment-Standard-Question-Set-Version-5.pdf — builduk.org, read 2026-09-24