Signing a Contract for Work Digitally: When Do You Need SES, AES or QES?

The refurbishment has been awarded, the tradespeople are on site, the quotation was confirmed by email. Then comes what comes on almost every building site: a design change, a substituted material, a variation order — discussed in passing, confirmed with a daywork sheet. Months later, the parties are not arguing about the original contract but about precisely those changes. The good news up front: a contract for work (Werkvertrag) is form-free in Switzerland [1] — legally, concluding one usually requires no signature at all, neither on paper nor electronically. The pitfalls lie elsewhere: with written-form clauses for variations, with the question of who on site was actually authorised to sign, with the assignment of defect rights, and with securities. This article shows which signature level is sufficient where — including the new construction-defect rules that have applied since 1 January 2026 [10].

Important: Status: 25 August 2026. This article is a general overview and not legal advice in an individual case. The concrete assessment depends on the wording of the contract, the general terms or SIA standards incorporated, and any public-law requirements.

The short rule

For a contract for work, too, the decisive question is not: "Are electronic signatures permitted?" It is: "Which form requirement applies to this one document?" That yields three cases:

1. No form requirement (the normal case): A contract for work under Art. 363 et seq. OR is not bound to any form (Art. 11 OR [1]). Legally, no signature at all is prescribed — an oral commitment or an email also creates a valid contract. Choosing the signature level here is purely a question of provability.
2. Statutory written form: Where the law requires written form under civil law (Art. 13 OR [1]), only the qualified electronic signature (QES) of a provider recognised in Switzerland satisfies that form electronically (Art. 14(2bis) OR [1]). This hardly ever applies to the contract for work itself — but it does apply to ancillary transactions such as the assignment of claims.
3. Contractually agreed written form: If the contract for work or the incorporated contractual conditions contain a clause such as "variations require written form", then in case of doubt the same applies to those documents as to the statutory written form — that is, QES (Art. 16 OR [1]). This is the biggest formal trap in construction.

On site, however, a fourth question arises that no signature level answers: who was authorised to act, and what exactly did their signature mean? Even a technically flawless QES only proves which natural person signed. It does not prove that this person was allowed to approve the variation on behalf of the client. More on this below — it is the most important section of this article.

The three signature levels in 60 seconds

In everyday practice, three levels of electronic signature are distinguished (ZertES also recognises further instruments such as regulated electronic signatures and seals [2]):

To place the AES: it can secure identity, document integrity and traceability considerably better than a simple signature. Its actual evidentiary weight, however, depends on the procedure used — identification method, certificate, audit trail and protection of the signature key are not equivalent for every AES [4]. The label "AES" alone guarantees no particular evidentiary value.

Only the QES satisfies the statutory written form (Art. 13–15 OR [1]) — combined with a qualified timestamp [4]. It must be based on a qualified certificate from a provider recognised under ZertES [2]. According to the BAKOM list, four providers are currently recognised: DigiCert Switzerland, Swisscom, SwissSign, and the Federal Office of Information Technology (only for the federal administration) [3]. Swiss QES can be checked free of charge via the federal validator [5].

Important for international constellations — for instance contracts for work with general contractors or suppliers from the EU: Switzerland and the EU still do not mutually recognise their signatures [3]. An eIDAS QES does not satisfy the Swiss written form; for form-free transactions, however, it can be used as an electronic or advanced signature.

1. Form-free: SES or AES is sufficient here

The principle of form-freedom (Art. 11 OR [1]) shapes the law on contracts for work almost throughout. These documents can be validly signed with any signature level — for evidentiary reasons, at least an AES is recommended:

Contract conclusion

• Quotations and order confirmations — acceptance by email or by click is valid too
• Contracts for work of any kind — construction, renovation, fit-out and refurbishment contracts, trade orders, individually produced works such as software or bespoke manufacturing
• Settlement and release agreements on disputed remuneration or defect claims

During execution

• Variations and change orders — provided the contract contains no written-form clause (see immediately below)
• Daywork sheets — regularly form-free; what matters is what the signature means (see the pitfall below)
• Site instructions and agreements on deadlines, prices or changes in execution

Acceptance and warranty

• Acceptance and handover protocols — list defects and reservations explicitly
• Notices of defects — form-free, but demanding in substance and bound to deadlines (new deadlines have applied since 2026, see below)
• Rectification agreements
• Withdrawal by the customer under Art. 377 OR — form-free; because of the full compensation obligation, this is economically the most delicate form-free document on this list. An AES plus provable delivery is not a formality here but self-protection.

A note for trade businesses in consumer business: if an order is initiated away from business premises — at the front door or by telephone — the right of withdrawal under Art. 40a et seq. OR may apply. The customer's withdrawal is not bound to any form but must be declared provably [1]. Here, too, documented receipt is what counts in the end.

Caution — written-form clause: If the contract for work, the general conditions, or an incorporated set of rules contains the clause "amendments and variations require written form", it is presumed that the parties do not wish to be bound before that form is met (Art. 16(1) OR [1]). If the clause says nothing more specific, the requirements of the statutory written form apply (Art. 16(2) OR) — variations then require a handwritten signature or a QES. The contract for work itself may therefore have been concluded form-free, while every single variation is form-bound. Anyone wanting to work digitally should word the clause accordingly:

"Amendments, additions and variations to this contract may, insofar as no mandatory statutory form requirement applies, also be agreed with an advanced electronic signature (AES)."

The reservation is important: where the law requires written form, the parties cannot lower it by a contract clause — there, QES or a handwritten signature always applies.

2. Statutory written form: QES or a handwritten signature is required

For the contract for work in the narrow sense, the law requires no written form. Form-bound, however, are typical ancillary transactions that occur regularly in a construction context — and that are not form-free simply because they sit inside a contract-for-work file:

The assignment of claims is the one most often overlooked in practice: when a newly built property is sold, the defect rights against the contractors are often assigned to the buyer. This assignment is a separate legal transaction subject to written form — electronically, that only works with a QES.

3. Securities: guarantee yes, suretyship no

On construction projects, securities are standard — performance guarantees, advance-payment guarantees, warranty guarantees. Here a distinction is worth making, because it decides the signature question:

• The guarantee under Art. 111 OR is form-free [1]. Bank and insurance guarantees in construction can therefore be issued and transmitted entirely digitally — with an AES or QES for evidentiary reasons.
• The suretyship is subject to strict form requirements (Art. 493 OR [1]). Suretyships given by natural persons require a public deed from CHF 2,000; below that, the maximum amount and any joint and several liability must be entered in the person's own handwriting in the deed. No electronic signature can reproduce either — suretyships by natural persons are effectively impossible to conclude digitally. For suretyships by legal entities and companies entered in the commercial register, simple written form suffices — electronically, that means QES.

The practical consequence: anyone who wants to handle securities digitally works with guarantees instead of suretyships — which in professional construction business is the standard anyway.

The biggest pitfall on site: variations, daywork sheets — and the question of who was allowed to sign

Disputes in construction and the trades rarely arise from the original contract. They arise from additional works, design changes, daywork and oral instructions on site. And here the best signature level does not help if two other questions remain open.

First question: which form applies to the variation? The order of examination: does the contract or the general conditions contain a written-form clause? Does it apply only to the conclusion of the contract, or also to variations and instructions? Does it require "written form", a "written agreement", or expressly an electronically signed declaration? Not every mention of the word "written" automatically leads to a QES — what matters is the wording and interpretation of the clause. In case of doubt, however, the presumption of Art. 16 OR applies: statutory written form, and therefore QES.

Second question: who was allowed to approve the variation? The signature level does not solve the authority problem. A technically flawless signed variation is not binding if the signing person was not allowed to approve it. The Federal Supreme Court has assessed contract-for-work cases on this point strikingly differently:

• Daywork sheets signed without reservation could, in the specific circumstances, count as subsequent approval and as an implied waiver of the written-form reservation (Federal Supreme Court 4A_377/2021 [6]).
• In another case, alleged additional works failed on the agreed written form and signature by both parties; the court warned against assuming implied contract amendments too readily (Federal Supreme Court 4A_51/2023 [7]).
• If the contract provides that additional works may only be carried out with the client's written consent, the contractor may not treat variation prices negotiated with site management as binding — merely incorporating SIA standard 118 does not give site management unlimited authority (Federal Supreme Court 4A_293/2025 [8]).
• And even where the parties have occasionally failed to observe an approval reservation, no general waiver may be inferred from that (Federal Supreme Court 4A_465/2017 [9]).

The message of this case law hits both sides: the contractor who relies on established practice risks their claim to remuneration. The client who systematically ignores its own written-form clause in daily business risks a court finding an implied waiver. Nobody should count on judicial generosity.

For drafting contracts, this means regulating the matter in three places — not in a single overloaded clause:

1. The form clause in the contract opens variations up to the AES (wording as above).
2. The competence rules — as a separate provision on authority — name exhaustively which persons or roles may approve variations, with which value limits, and make clear that site management does not bind anyone to variation prices without express authority.
3. The clarification on the daywork sheet itself: "Signing this sheet confirms the nature, scope and timing of the services recorded. It does not constitute approval of a variation unless this is expressly declared." This clarification must appear where the signature is given — buried in the contract, it is of no use on site.

All three levels can be modelled cleanly in digital form: signature level, approval role and value limit are configured and enforced per document type in the workflow, instead of relying on discipline on site.

New since 2026: the construction-defect reform raises the stakes

Revised rules on construction defects have applied since 1 January 2026 [10]. The key points:

• For immovable works, a 60-day notification period applies from acceptance or from discovery of the defect (Art. 367(1bis), Art. 370(4) OR [1]). The period is partially mandatory: shortening it is excluded, extending it remains permissible [11].
• It also applies to movable works that are integrated into an immovable work as intended (windows or heating systems, for instance), as well as to architectural and engineering services that serve as the basis for a building [10].
• The right to free rectification of construction defects can no longer be excluded in advance — not even down the subcontractor chain [10].
• Where SIA standard 118 is incorporated, the two-year notification period for apparent defects remains in place (it is longer than the statutory minimum); the duty to notify defects discovered later "immediately", by contrast, is overridden by the 60-day period [11].
• Transitional law: the new rules apply to contracts concluded from 1 January 2026. Previous law applies to older contracts [11] — blanket statements are out of place here.

The reform changes nothing about the signature level: the notice of defects remains form-free. But it sharpens what matters in that notice — deadline, content and receipt. A notice that arrives too late, that fails to substantiate the defects, or whose delivery cannot be proven, causes the defect rights to lapse. The AES secures who declared what and when; it does not automatically prove receipt by the counterparty. A digital defect-notice process therefore needs both: the signature and a robust, documented delivery channel.

Special case public procurement: the exception to the short rule

For federal administration procurement contracts, a striking exception to the rule "written form = QES" applies: the Ordinance on Public Procurement (VöB) does require written form, but the BKB and KBOB interpret this broadly — as written or in another form that allows proof by text. Email correspondence and digital contract conclusion with electronic signatures of every level are expressly included; written form under the VöB is precisely not the same as written form under the OR [12]. Which level is used in a specific case is determined by the contracting authorities on the basis of a risk-benefit assessment and communicated in the call for tenders or the tender documents.

For contractors this means: what governs are the call for tenders, the contract documents and the contracting authority's requirements — not the civil-law short rule. The guidance note is addressed to the federal administration; cantons and municipalities may have their own requirements, which must be checked separately.

Legally valid, provable, binding: three questions, three answers

For contracts for work, three levels belong apart that are constantly mixed up in daily business:

• The legal position: is the declaration valid at all in this form? Only the law answers that — or your own contract clause. A form-free contract for work is just as valid with an SES as with a QES.
• Provability: can I demonstrate in a dispute who signed what and when — and that the declaration was received? Here the levels part ways: an SES is easily contestable; AES and QES attribute the signature to an identified person and secure document integrity (Art. 2 ZertES [2]).
• Binding effect: was the signing person authorised to bind the company or the client at all? No signature level answers that question — it belongs in powers of attorney, competence rules and the approval workflow.

What is legally required is not up for debate. Where form-freedom applies, the choice of level is a risk assessment — the higher the contract value, the likelihood of a dispute and the need for evidence, the higher the level. But it is the third level that most often decides whether a case is won or lost on site.

Overview: which signature for which document?

Legend: ✅ = legally valid in this form · ❌ = does not satisfy the required form · Basis: Code of Obligations (OR) [1], unless stated otherwise.

How to read the table: ✅/❌ reflects the legal position (valid or not), the last column the practical residual risk if the lowest permitted level is chosen.

Recommendations for practice

1. AES as the standard for the entire contract-for-work file (practice recommendation). From the contract through the variation to the acceptance protocol, the AES offers the best ratio of legal certainty, evidentiary value and user-friendliness — without prior identification at QES level.
2. QES wherever written form applies (legally required). For contracts for work, that means above all assignments of claims under Art. 165 OR and variations under imprecise written-form clauses. Anyone wanting to work digitally here cannot avoid the QES.
3. Modernise written-form clauses. The AES-opening clause in the contract spares you the QES obligation on every variation (Art. 14(2bis) OR permits deviating agreements [1]) — subject to mandatory statutory form requirements.
4. Approval roles and value limits into the workflow. The competence rules belong in the contract, the daywork-sheet clarification on the sheet itself — and both belong in the digital signature process, which enforces level and role per document.
5. Don't forget delivery. The signature does not replace proof of receipt. Notices of defects, withdrawals and other deadline-bound declarations need a provable delivery channel.
6. Structure securities as guarantees. Guarantees under Art. 111 OR are form-free and can be handled fully digitally; suretyships by natural persons cannot.
7. Electronically signed stays electronic. The signed original PDF is archived electronically — ideally in a long-term format (PAdES-LTA) with a qualified timestamp. The printout is only a copy without a verifiable signature.

FAQ

Does a construction contract require a QES? No. A contract for work is form-free and can be validly concluded with any signature level — in theory even orally (Art. 11 OR [1]). A QES only becomes necessary once the law or the contract requires written form, for example for an assignment of claims or under a written-form clause.

Is a signature on a tablet on site sufficient? As an SES it is legally valid for form-free documents. Its evidentiary value is limited, though: who signed, which version of the document was on screen, and what did the signature mean? For daywork sheets and acceptance protocols, an AES with a clear statement about the meaning of the signature is the better standard.

What applies to variation orders? Read the contract first: with no form clause, the variation is form-free (AES recommended). With a written-form clause that says nothing more specific, QES applies in case of doubt. And regardless of form: only the persons named in the contract can validly approve variations — site management has no unlimited authority without express power of attorney (Federal Supreme Court 4A_293/2025 [8]).

Does SIA standard 118 require a particular signature level? No. Incorporating SIA standard 118 does not determine a signature level. It does govern competences and procedures — and the individual contract for work can restrict those competences further. Questions of form and authority must always be checked against the individual contract.

What changes with the new construction-defect rules since 2026? For contracts concluded from 1 January 2026, a mandatory 60-day notification period applies to both apparent and hidden defects in construction works, and the right to free rectification can no longer be excluded in advance [10]. This does not change the signature level — but it makes a clean, deadline-proof defect-notice process with proof of receipt all the more important.

Can I sign a performance guarantee digitally? Yes — a guarantee under Art. 111 OR is form-free and can be issued fully digitally with an AES or QES. A suretyship given by a natural person cannot: it requires a public deed or handwritten statements of the amount, which no electronic signature can replace.

Is an email confirmation sufficient? For form-free transactions, yes — the contract is validly concluded. In a dispute, however, the question arises who wrote the email and which version of the document was meant. For anything beyond small orders, the AES is the more robust choice.

Conclusion

Swiss law on contracts for work is digital-friendly: the entire life cycle — quotation, contract, variation, daywork sheet, acceptance, notice of defects — works fully electronically, in most cases already with an AES. The QES is used selectively where the law or the contract requires written form: for assignments of claims and under imprecise written-form clauses. The real risks, however, lie not in the technology but in three questions that must be answered before the first signature: which form applies to this document? Who may sign it with binding effect? And what exactly does the signature on the daywork sheet mean?

The decisive factor is that the signature solution enforces these answers. With actaSIGN, clients, general contractors and trade businesses define the required signature level for every document in the workflow, from SES to QES — including the approval roles for variations; the qualified signatures are issued via Swisscom, a provider recognised under ZertES.

Further Reading

• SES, AES, QES: the three signature levels explained
• Qualified electronic signature (QES): the guide
• HR documents in Switzerland: which signature for which document?
• Signing a rental agreement digitally: when do you need SES, AES or QES?
• Electronic signature in Switzerland: legal framework and practice
• Signature solution for SMEs
• Request a demo

Sources

1. Code of Obligations (OR, SR 220) — in particular Art. 11, 13–16, 40a et seq., 111, 165, 363 et seq., 367, 370, 377 and 492 et seq.
2. Federal Act on Electronic Signatures (ZertES, SR 943.03)
3. BAKOM — Electronic signature, list of recognised providers
4. Federal Office of Information Technology (BIT) — E-signature FAQ
5. Federal signature validator
6. Federal Supreme Court 4A_377/2021 of 29 June 2022 — daywork sheets as subsequent approval
7. Federal Supreme Court 4A_51/2023 of 23 May 2023 — written-form reservation for additional works
8. Federal Supreme Court 4A_293/2025 of 29 September 2025 — authority of site management over variation prices
9. Wyss, Die Mehrforderung — Anlass zu steten Auseinandersetzungen im Bauwerkvertragsrecht (Bratschi), citing Federal Supreme Court 4A_465/2017
10. HEV Schweiz — Revision of construction contract law as of 1 January 2026
11. GGO — Notification period for defects: what changes from 1 January 2026 (incl. relationship to SIA standard 118 and transitional law)
12. BKB/KBOB — Guidance note: use of electronic signatures for concluding procurement contracts (March 2023, updated April 2026)
13. Birchmeier/Brunner, Liability for construction defects from 1 January 2026, Jusletter 15 December 2025
14. Legislative text of the construction-defect reform — BBl 2025 18

---

This article reflects the legal status as of August 2026 and does not replace legal advice in individual cases — precisely with written-form clauses, questions of authority and deadlines, the concrete wording of the contract decides. The research was carried out with the support of artificial intelligence; the legal bases cited were verified against the primary sources (Fedlex, Federal Supreme Court, BKB/KBOB, BAKOM). The article was reviewed and edited by a natural person before publication.