A plain-English guide for Belgian subcontractors, what you must register, what you are entitled to, and how chain liability changes the rules when you work for a main contractor.
If you are a Belgian subcontractor or self-employed builder, the Check in at Work (CIAW) rules can feel like they were written for someone else. The thresholds reference the main contractor’s contract, the inspectors usually arrive at the site office rather than your van, and the fines hit whoever the NSSO can identify fastest. In reality, subcontractors carry real obligations, and equally real rights, under Belgian chain-liability rules, and the Check in at Work framework treats you as a registered participant on every site you set foot on. This guide explains exactly what you must do, what the main contractor is legally responsible for, and what protections you have when something goes wrong. It is written for the person running a small subcontracting business and trying to stay out of inspector trouble without buying enterprise software they do not need.
Quick Navigation
- When does CIAW apply to you as a subcontractor?
- Your obligations on someone else’s site
- Your rights under Belgian chain liability
- Using the main contractor’s CIAW app vs your own
- Common subcontractor traps and how to avoid them
- Subcontractor obligations at a glance
- Managing CIAW with technology
- Frequently Asked Questions
When does CIAW apply to you as a subcontractor?
Check in at Work is mandatory in construction for any site where:
- The total contract value exceeds €500,000, in this case, all subcontractor work on the project is in scope, regardless of individual contract size.
- Your own subcontractor contract exceeds €5,000 in value.
- There are two or more subcontractors involved on the project at any time, in which case every subcontractor must register, regardless of contract size.
For cleaning the threshold is €30,000, for the meat sector €5,000. The legal framework is published on the Belgian Social Security portal and detailed in the NSSO official guidance.
In practice, almost any subcontractor working on a site that has a main contractor will be in scope. If you are unsure, ask the main contractor for written confirmation; if they cannot give you a clear answer, treat the work as in scope and register. The downside of registering an exempt job is zero; the downside of not registering an in-scope job is administrative or criminal sanctions per offence, refer to the NSSO Check in at Work guidance for current amounts.
| ⚠️ Important regulatory warning: Subcontractor obligations apply per worker, per day, per site. A subcontractor with three workers on a site for five days without registration could face up to €90,000 in criminal sanctions in the worst case. The Belgian Data Protection Authority also enforces how worker data is handled, registrations must be accurate and minimal. |
Your obligations on someone else’s site
When you work as a subcontractor under a main contractor, you have three core obligations:
- Register every worker, every day, on every site. This includes yourself if you are also working on site. Use either the main contractor’s CIAW app or your own, but the registration must end up in the NSSO record.
- Use the correct worker identity. The Belgian rijksregisternummer (NISS) is required for Belgian workers; non-Belgian workers need a BIS number and a valid Limosa declaration before they start.
- Inform your own subcontractors. Chain liability cascades. If you bring in a third party (a “sub-subcontractor”), you are responsible for their compliance the same way the main contractor is responsible for yours.
Beyond these, you should always:
- Keep your own internal record of registrations, do not rely entirely on the main contractor’s system.
- Document any technical issues that prevented timely registration (screenshots, time-stamped notes).
- Notify the main contractor immediately if your registration fails, they have an interest in helping fix it before an inspection.
Your rights under Belgian chain liability
Chain liability is often discussed as a burden on the main contractor, but it gives subcontractors important protections too.
✅ You have the right to use the main contractor’s CIAW system at no charge to you, where the main contractor has chosen to provide one.
✅ You have the right to receive a clear, written briefing on which CIAW method is in use on the site (app, site pole, badge), and where to escalate issues.
✅ You have the right to access your own registration data, to verify your hours, exports for invoicing, and as a defence in any wage or social-security dispute.
✅ You have the right to refuse work on a site where the main contractor cannot show that CIAW is in place, if the work is in scope. Reasonable refusal protects you from being dragged into a chain-liability case.
✅ You have a right to be treated as the responsible employer for your own workers, the main contractor cannot dictate how you manage your team beyond the registration obligation itself.
If a main contractor pressures you to “skip the registration today” or “we’ll backdate it,” refuse in writing. The risk falls on both of you, and your written record of objection becomes important if an inspection follows. The Suivo CIAW FAQ summarises the most common chain-liability disputes.
Using the main contractor’s CIAW app vs your own
For small subcontractors, this is the most practical decision.
❌ Running five different CIAW apps because every main contractor uses a different one
✅ Using each main contractor’s app for that contractor’s sites and keeping a personal export each week
❌ Refusing to use the main contractor’s tool, then being treated as non-compliant
✅ Accepting the main contractor’s onboarding and documenting any concerns separately
For larger subcontractors with their own workforce across multiple sites, having your own platform, synced via chain-liability dashboard with main contractors, is usually the better path. It gives you continuity, your own audit trail, and integration with your payroll. Suivo’s CIAW solution supports both modes: your team can use your platform while still appearing in the main contractor’s chain-liability view.
If you operate across construction, concrete, and transport, a single integrated platform avoids the cost of running parallel systems and gives you a coherent record for all your inspections.
Common subcontractor traps and how to avoid them
| Trap | Why it happens | How to avoid |
| Believing CIAW is the main contractor’s problem | Misreading chain liability | Register regardless; main contractor liability does not absorb yours |
| Backdating registrations after an inspection | Pressure to fix gaps | Refuse; backdating is sanctionable in itself |
| Sharing one CIAW login between workers | Trying to save licences | Each worker must have their own identity; sharing is a violation |
| Skipping Limosa for posted workers | Treating it as paperwork | File Limosa before any CIAW account is created |
| Relying only on the main contractor’s record | Convenience | Keep your own weekly export |
| Sub-subcontractors left unregistered | “Not my responsibility” | Chain liability cascades; you are responsible |
| Refusing to discuss CIAW with the main contractor | Avoiding conflict | Raise issues early in writing; a documented objection protects you |
If you avoid all seven traps, you eliminate roughly 90% of the issues subcontractors typically face during NSSO inspections.
Subcontractor obligations at a glance
| Situation | Must register? | Whose system | Key documents |
| Construction main contract > €500,000 | ✅ Yes, every worker | Main contractor’s, or yours synced | Worker NISS or BIS, Limosa if posted |
| Your subcontract > €5,000 (smaller project) | ✅ Yes | Main contractor’s, or yours synced | As above |
| 2+ subcontractors on site | ✅ Yes, all parties | Main contractor’s, or yours synced | As above |
| Cleaning contract > €30,000 | ✅ Yes, entry and exit (CIAO) | As above | As above |
| Meat sector work > €5,000 | ✅ Yes | As above | As above |
| Private residential, no other sub, < threshold | ❌ Generally no | n/a | Keep contract for proof |
Always confirm in writing with the main contractor; do not rely on verbal exemption.
Managing CIAW with technology
Suivo, a Belgian IoT and compliance company with over 15 years of experience, builds CIAW tooling that supports both main contractors and subcontractors in the same chain-liability ecosystem. Their platform helps you:
- Register each of your workers on every main contractor’s site using a single app, with the CIAW solution handling NSSO submission automatically.
- Extend natively to CIAO when working in the cleaning sector, with entry and exit timestamps.
- Keep your own auditable record, independent of the main contractor’s system, and export weekly for invoicing.
- Sync directly to your payroll provider (SD Worx, Partena, Acerta) via the time tracking module, cutting the hours spent on weekly admin.
- Receive automatic chain-liability alerts when one of your own sub-subcontractors fails to register on time.
- Work across construction, concrete, and transport sites without switching platforms.
- Get NL/FR/EN local support from a Belgian team that understands subcontractor reality.
Suivo’s IoT platform integrates seamlessly with existing payroll and ERP systems, helping subcontractors who work for companies like Hoogmartens, Cegelec, and Van Moer keep their own records aligned with the main contractor’s chain-liability dashboard.
“We work for five different main contractors, each with their own app. Having our own Suivo account in parallel meant we always had our records ready, and the one time an inspector came to our office, we exported a clean two-year history in under five minutes.”, Owner, specialist subcontractor, Mechelen region
Take Action Today
Don’t let chain-liability assumptions catch your subcontracting business off guard. Start by listing every active site, confirming with the main contractor in writing which CIAW system applies, and keeping your own weekly export, even when you are using the main contractor’s tool.
For more information about CIAW for subcontractors, contact Suivo at +32 3 375 70 30 or visit the Suivo CIAW solution page to see how their platform supports subcontractor independence within main-contractor chains. You can also explore the full product range, browse current pricing, or book a demo.
Free Subcontractor Compliance Guide
Want to know exactly where you stand on every site? Our free Subcontractor Compliance Guide gives you a structured way to track your CIAW obligations across multiple main contractors without losing your own audit trail.
Inside, you’ll find:
- A site-by-site obligation map covering construction, cleaning, and meat sectors
- How Suivo helps subcontractors stay independent while syncing into chain-liability dashboards
- Real-life lessons from subcontractors working for Hoogmartens, Cegelec, and Van Moer
- Practical templates: subcontractor onboarding letter, refusal-of-non-compliance memo, weekly audit log
Frequently Asked Questions
If the main contractor handles CIAW, do I still need my own system?
Strictly speaking, no, you can rely on the main contractor’s system for that site. But for any subcontractor working across multiple main contractors, keeping your own records via a tool like the Suivo CIAW solution is the only way to maintain a single, defensible audit trail.
Can I be fined if the main contractor failed to set up CIAW on the site?
Yes. Belgian chain liability is bidirectional: the main contractor is responsible for ensuring CIAW is in place, but as the subcontractor, you are still expected to register your workers. If the main contractor’s system is missing, you can register through your own tool or the official government portal, and document your effort in writing.
Do I need CIAW if I’m a one-person self-employed contractor?
Often yes. The thresholds apply to the contract, not the headcount. A self-employed builder working on a project above the threshold or alongside other subcontractors must register the same as a larger company. Check the Suivo CIAW FAQ for the most common one-person scenarios.
What about my own sub-subcontractors?
Chain liability cascades downwards. If you bring in a sub-subcontractor, you are responsible for ensuring they register, just as the main contractor is responsible for you. Use the construction industry chain-liability features of your CIAW platform to spot gaps in real time rather than waiting for an inspection.
