Subcontracting in construction: contract, reverse-charge VAT and due diligence

Subcontracting is not outsourcing your liability

Using a subcontractor is often essential — overload, or a technical trade outside your specialty. But legally, you remain liable to your client, and the authorities impose precise obligations towards the subcontractor. Three locks to put in place.

Lock 1 — The written contract

The verbal deal — "you do the plumbing, I'll pay you at the end" — is a time bomb. The subcontracting agreement should set out at minimum:

• the exact scope of the delegated works (with plans/quotes attached);
• the price and payment terms (deposit, progress payments, retention);
• deadlines and any penalties;
• the subcontractor's insurance covering the delegated activity — check the certificate, not the promise.

On private projects with an owner, also have the subcontractor formally accepted by the end client.

Lock 2 — Reverse-charge VAT

In French construction, subcontracting falls under the reverse-charge mechanism: the subcontractor invoices excluding VAT with the "Autoliquidation" mention, and you, as principal, account for the VAT on those works.

Classic error: a subcontractor invoicing with VAT. If you pay it, it is not deductible — you lose it, and you're exposed to a fine on top. The reflex: refuse any subcontracting invoice with VAT and request a corrected invoice.

Lock 3 — Due diligence

Above €5,000 excl. VAT, you must collect the subcontractor's social-security compliance certificate every six months (plus proof of registration). Failing that, if they are caught for undeclared work, you can be held jointly liable for their social and tax debts.

File these documents per project, with renewal reminders: it's tedious — exactly the kind of discipline your software should carry for you.

In short

Signed contract, reverse-charge invoices, up-to-date certificates: three habits that turn subcontracting from a legal risk into a genuine growth lever. In Aidifis, your subcontractors' documents attach to the project and its deadlines — nothing gets lost in email threads anymore.