Signing works contracts digitally: which signature do you need?

Settle the question of form first

Swiss law follows the principle of freedom of form (Art. 11 of the Code of Obligations, CO). A contract for work under Art. 363 et seq. CO is therefore valid without any particular form: orally, by e-mail or with any kind of electronic signature. The signature question only becomes delicate when a specific form is required.

No form required: most works contracts, orders, acceptance records and defect notices. Here the main concern is evidence.
Contractual written-form clause: if the parties agreed on written form, for example for variations, it applies. Without a closer definition, a signature equivalent to a handwritten one is required in case of doubt.
Statutory written form: for example for the assignment of claims. Electronically, only a qualified electronic signature with a qualified time stamp meets this requirement (Art. 14 para. 2bis CO).
Notarisation: for instance for real estate transactions or, depending on the amount, guarantees by private individuals (Bürgschaft). Even a qualified signature does not replace the notary here.

Security can often be structured as a guarantee under Art. 111 CO, which requires no form and can therefore be handled entirely digitally.

The three signature levels at a glance

Level	Typical use in construction	Assessment
Simple electronic signature (SES)	Small orders, receipts, internal approvals, signing on a tablet	Valid where no form is required, but weak evidential value
Advanced electronic signature (AES)	Works contract, variations, acceptance records, daywork reports, defect notices	Identity and integrity of the document can be proven
Qualified electronic signature (QES)	Statutory or contractual written form, such as assignments of claims	The only level equivalent to a handwritten signature

For most documents around a works contract, the AES is a sensible standard: easy to use and much easier to prove in a dispute than a scanned signature image. The QES should be used specifically where a form requires it.

Variations, daywork reports and defect notices

The critical moments on site are rarely technical. A correctly signed variation does not bind the client if the signatory had no authority to approve it. The site management is not automatically entitled to approve additional costs. Set out in writing who may approve variations and up to what amount.

The same goes for daywork reports: does the signature only confirm that the hours were worked, or also that the work will be paid as an extra? This clarification belongs on the report form itself, not just in the contract.

New rules on construction defects since 2026

Under the revision of the CO in force since 1 January 2026, defects in buildings must be notified within 60 days of discovery, and the right to free remedial work can no longer simply be excluded in advance. Which rules apply to a given contract depends, among other things, on when it was concluded. If in doubt, check the current position with a specialist. This does not change the signature level, but it does make deadline, content and proof of receipt of the notice more important.

The process in five steps

Check the form: none, contractual written-form clause or statutory form?
Set the signature level: AES as standard, QES where written form applies.
Define authority: who may sign which documents up to what amount?
Invite signatories in the correct order and have them sign.
Prove delivery of time-bound declarations and archive the signed original electronically.

On the last point: a printed copy of an electronically signed PDF loses its evidential function. Only the electronic original file with a valid signature has probative value.

Typical mistakes and choosing a solution

Signing variations without checking the written-form clause in the contract.
Assuming the QES is automatically the safe choice even when authority is unclear.
Using daywork reports without stating what the signature means.
Sending defect notices without proof of receipt.
Printing signed documents instead of storing them digitally.

For one-off cases, a lean process with a recognised signature service is often enough. Once many variations, several parties and deadlines come together, a platform that enforces the required signature level and approval roles per document type is worthwhile. Look for a QES under Swiss law (ZertES) from a recognised provider, a complete audit trail, data storage in Switzerland or a country with adequate data protection, and tamper-proof archiving.

Frequently asked questions

Does a works contract need a qualified signature?

No. A works contract requires no form and is valid with any signature level. A QES is only needed where the law or the contract requires written form.

What applies to variations?

Read the contract first. Without a form clause, the variation requires no form and an AES is recommended. With a written-form clause that is not defined further, a QES is needed in case of doubt. It is simpler to expressly open the clause to the AES in the contract.

Is a signature on a tablet on site enough?

As a simple electronic signature it is valid for documents without form requirements, but its evidential value is limited. For daywork reports and acceptances, an AES with a clear statement of what the signature means is the better standard.

Does a QES replace notarisation?

No. Where the law requires notarisation, for example for property purchases, a notary is still needed.

How do I prove that a defect notice arrived in time?

With proof of delivery, for example via a signature platform with receipt confirmation, registered mail or a written confirmation from the recipient. Carefully record the date of discovery and the content of the notice.

This article is general information and not legal advice for individual cases.