A question the SPN engineering team often receives is "Does this work need a Senior Professional Engineer's signature?" The answer has two layers. The first is the minimum the law sets. The second is whether the project owner or the project requirements specify more than the law. Understanding both layers helps you avoid hiring below the required level, so the drawings are rejected, or above what is needed, at extra cost.
Under the COE regulations, what work must be done only by a Senior Professional Engineer?
The Council of Engineers Regulation on Criteria and Qualifications of Controlled Engineering Practitioners at Each Level, Civil Engineering Branch, B.E. 2566 (2023) allows a Senior Professional Engineer to practice in all work of every size, and also allows a Professional Engineer to carry out design, calculation, project planning, construction supervision, review and inspection, and operational direction of every size. The only work the law reserves for Senior Professional Engineers is consulting in the form of diagnosis and certification, while a Professional Engineer may provide consulting only in the form of advice.
"Consulting" in this sense is work where the engineer is not the designer or supervisor, but gives an engineering opinion on someone else's work or on existing conditions — for example, diagnosing the cause of structural damage, giving an opinion on whether another party's design or construction is correct, and certifying as an independent consultant. Work of this kind therefore requires a Senior Professional Engineer directly. The full table of scope for each grade is in Engineer license grades: which drawings each can sign.
Which work can a Professional Engineer do, but in practice often requires a Senior Professional Engineer?
Project owners and the relevant authorities may set signatory qualifications above the legal minimum according to the risk of the work. From SPN's project experience, work that often comes with a requirement for a Senior Professional Engineer includes:
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| Type of work | Minimum per 2023 regulation | Often found in project requirements |
|---|---|---|
| Design of a residential house ≤ 4 storeys, not a public building | Associate Engineer | Associate or Professional Engineer |
| Design of high-rise, large or public buildings, and bridges | Professional Engineer | Professional Engineer · large public-sector projects often specify a Senior Professional Engineer as design team leader |
| Certifying the structural safety of an existing building before an extension, alteration or change of use | Professional Engineer (review and inspection) | Senior Professional Engineer — relevant authorities and building owners usually want a signatory with no scope restriction |
| Engineering opinion in disputed work, insurance claims or court proceedings | Senior Professional Engineer (diagnostic consulting) | Senior Professional Engineer |
| Certifying drawings or work designed by others (independent check) | Senior Professional Engineer (certification consulting) | Senior Professional Engineer |
| Design of deep foundations, excavation support for deep excavations, high retaining walls in soft soil | Professional Engineer | Professional Engineer · work adjacent to existing buildings or with an EIA often requires a Senior Professional Engineer to co-sign |
| Building inspection after an event (earthquake, fire, settlement) | Professional Engineer (review and inspection) · if it is diagnosis as a consultant = Senior Professional Engineer | Senior Professional Engineer, when the inspection results are used to decide whether the building stays in use |
Note that the dividing line is the "role" rather than the "size" — for the same work, if the engineer is the designer, a Professional Engineer can do it; but if the engineer is hired to give an opinion on or certify someone else's work, it becomes consulting work that requires a Senior Professional Engineer. Examples of building inspection work of this kind: structural assessment of old buildings, pre-purchase building inspection (due diligence) and post-earthquake building inspection.
What documents does a Senior Professional Engineer sign?
Documents certified by an engineer fall into 4 groups. The first is construction drawings and calculations submitted to the relevant authority for a building permit (see the contents in What is a structural calculation report?). The second is structural safety certificates for existing buildings or structures. The third is inspection and assessment reports, such as non-destructive structural inspection reports and damage assessment reports. The last is engineering opinion letters for consulting work or disputes.
Every document must state the signatory's name, license registration number and grade, which the relevant authority can check against the Council of Engineers database immediately. Using a lower grade than the project requirements specify therefore gets the submission rejected at document review.
Can you hire a Senior Professional Engineer to "just sign" without doing the design?
No, not in the sense of signing without checking. An engineer who signs drawings, calculations or certificates is responsible for their content under the Engineer Act B.E. 2542 (1999) and the Council of Engineers code of ethics. Signing work one has not done or has not actually checked is an ethics violation and may lead to suspension or revocation of the license.
What can properly be done is to hire a Senior Professional Engineer to review and certify work designed by others: the Senior Professional Engineer reviews the assumptions, the calculations and compliance with the law, and then signs as the certifying engineer. This process takes time and is charged according to the amount of work to be checked, not as a signature fee. General costs of design and checking are covered in How structural design fees are priced. SPN quotes each project individually; contact us for a free quotation within 24 hours. Prices do not include travel and equipment mobilization, which are charged extra according to the distance to the site when a site inspection is needed.
Checklist before hiring: does your work need a Senior Professional Engineer?
Ask yourself 4 questions. Question 1: Is this your own design or supervision, or an opinion on/certification of someone else's work? — If the latter, a Senior Professional Engineer is required. Question 2: Do the tender documents, contract or conditions of the relevant authority specify the signatory's grade? — If they specify a Senior Professional Engineer, follow that. Question 3: Will the results be used to decide the safety of an occupied building, or in a dispute? — If yes, a Senior Professional Engineer helps reduce challenges over the signatory's qualifications. Question 4: If none of the three applies, a Professional Engineer is enough, and an Associate Engineer can handle small residential houses. See the scope in Scope of a civil Associate Engineer.
Whatever the grade, always check the license status at coe.or.th before signing, and keep a copy of the signatory's license with the project documents.
This content summarizes the COE Regulation on the Civil Engineering Branch B.E. 2566 (2023) and project experience. Requirements may differ between projects and between relevant authorities. Clients should always check the conditions of their own work and the current regulations. SPN does not guarantee the decision of any authority.