Limosa Declaration in Belgium: A Guide for Subcontractors

What Limosa Is and Who It Applies to in the Construction Industry

Limosa is Belgium's mandatory registration system for posted workers. It applies to every subcontractor from an EU or EEA country that sends workers to perform work on Belgian territory. The legal basis is the Belgian Act of 5 March 2002 implementing Directive 96/71/EC on the posting of workers, and the Act of 5 March 2017 on chain liability in the construction sector.

When it comes to sandwich panel installation — both façade and roofing — the Limosa declaration is not optional. Belgian labour inspectorates, Sociale Inspectie and Inspection sociale, actively inspect job sites in the industrial and commercial building envelope sector. The administrative penalty for failing to file a declaration ranges from €400 to €4,000 per worker. In criminal proceedings, fines can reach €25,000 per worker or €250,000 for the employer.

The registration requirement applies to every posted individual: the site manager, Kingspan or Ruukki panel installers, crane operators, and forklift operators. An exemption exists for postings shorter than 5 working days within any 4 consecutive weeks, but it covers only a narrow list of activities. Façade and roofing installation does not qualify for this exemption.

The Limosa Declaration: Step by Step

Employer Registration on the LIMOSA Portal

The first step is registering your company on the portal at www.limosa.be. The portal is available in Dutch, French, German, and English — there is no Polish version. Registration requires:

• the company's registration number from its home country (or equivalent)
• EU VAT number
• contact details of the person responsible for declarations
• a Belgian NISS number, if the company has previously operated in Belgium

Account verification by the Belgian authority ONSS/RSZ takes 1–3 working days. Do not leave this to the last moment — the worker declaration must be submitted before the first day of work on Belgian soil. Allow at least one week for account activation before mobilising the crew.

Submitting the Worker Declaration and the Limosa-1 Certificate

Once the employer account is active, individual declarations can be filed. Each posted worker requires a separate submission. Information required in the form:

• first name, surname, date of birth, nationality
• identity document or passport number
• home address in the sending country
• start and end dates of the posting
• exact site address: street, number, postcode, municipality
• NACE activity code — for panel installation this is typically 43.99 (other specialised construction activities)
• Belgian client details: the project owner or main contractor

Once the declaration is correctly submitted, the system generates a Limosa-1 certificate in PDF format. Each worker must have this document on them throughout the entire period of work in Belgium — either in paper or electronic form. In practice, the most convenient approach is to send the certificate directly to each installer's phone before departure.

The most common mistake: if installation runs beyond the declared end date, the declaration must be updated before the original period expires — not after. The Belgian inspectorate checks date compliance, and any discrepancy between the certificate and the actual situation is treated the same as having no declaration at all.

The A1 Form — a Separate Obligation, Not an Alternative

The Limosa declaration is a Belgian registration requirement. Separate from it is the A1 form, issued by the social insurance authority in the worker's home country — it confirms that the worker remains subject to social security in their home country and not in Belgium. The Belgian inspectorate requires both documents simultaneously. An absent A1 form, even alongside a valid Limosa-1 certificate, can result in Belgian social security contributions being assessed retroactively for the entire posting period.

Chain Liability and Documentation for the Main Contractor

The Belgian Chain Liability Act (wet ketenaansprakelijkheid) requires the main contractor to verify a subcontractor's documents before allowing them on site. A main contractor who fails to carry out this verification is jointly and severally liable for any unpaid contributions and penalties imposed. In practice, this means that before entering the site, the subcontractor provides the main contractor with a complete set of documents:

• Limosa-1 certificates for all posted workers
• A1 forms for the same individuals
• company details: EU VAT number, registered address, company registration number
• name of the person responsible on site

Belgian clients and main contractors increasingly require these documents to be submitted in advance — typically a minimum of 48 hours before mobilisation. Projects carried out using ArcelorMittal Cofraplus, Ruukki, or Kingspan QuadCore systems generally involve several phases with crew rotations: structural frame, façade cladding, flashings, and sealing. Every change in crew composition requires the declarations in the Limosa system to be updated. A single declaration per project is not sufficient — the obligation is tied to specific individuals and specific dates.

Registration in the Limosa system is free of charge. Compliance costs amount to the time of the person responsible for documentation and, where applicable, the fee of a mandataire — an authorised representative engaged by companies that cannot navigate the portal in a foreign language on their own.

Before any project in Belgium, three steps must be completed in a fixed order: verify that the employer account in Limosa is active, obtain A1 forms for all workers being sent, and provide Limosa-1 certificates to the main contractor before mobilisation — not on the day the crew arrives on site. Subcontractors who have turned this sequence into a routine lose no time dealing with inspectors and do not risk having work stopped halfway through a façade installation.