Homeowners, contractors and factory engineering departments often already have drawings or a structure, but lack the "engineer's signature" required by the permitting authority, a bank, an inspector or a contract party. This page explains what kinds of work SPN can certify, who signs, what you need to prepare and how the process works, so that you get documents that can actually be submitted and that comply with Thailand's engineering law.
What does SPN's certification service cover?
SPN certifies 4 groups of work: structural drawings and calculations, engineer's certificates for permit applications, certificates of structural soundness for existing buildings or structures, and foundation certification based on soil investigation and pile test results. All groups are signed by a civil engineer with a professional engineering license at the Senior Professional Engineer grade, the grade that the COE Regulation of B.E. 2566 (2023) permits to practice civil engineering on all types and sizes of work.
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| Services | When it is needed | Documents you receive |
|---|---|---|
| 1. Certification of structural drawings and calculations | Permit applications for construction, alteration or extension, or when a contract party requires engineer-signed drawings | Checked structural drawings and calculations signed by the engineer on every sheet + copy of the COE license |
| 2. Engineer's certificate (designer/calculation engineer) | Supporting a building permit application to the district office, municipality or SAO (Subdistrict Administrative Organization) under the Building Control Act | Certificate from the licensed professional engineer with a copy of the license |
| 3. Certificate of structural soundness of an existing building/structure | Change of use, installing machinery, rooftop solar panels or storage racks, extensions on an existing building, sale/purchase, or when a bank or insurer requires it | Structural inspection and assessment report + certificate signed by a Senior Professional Engineer (site inspection and non-destructive structural testing may also be required) |
| 4. Certification of foundations and pile load capacity | When pile size/length or spread footings must be confirmed from actual soil data | Foundation calculations referencing soil investigation or pile test results, signed by the engineer |
Who signs, and why a Senior Professional Engineer?
The signatory is an SPN civil engineer holding a Senior Professional Engineer license, the highest grade of professional engineering license. The COE Regulation on the criteria and qualifications for each grade of licensed professional engineer in civil engineering, B.E. 2566 (2023), limits the scope of Associate Engineers and Professional Engineers by building type and size — for example, an Associate Engineer may design buildings of no more than 4 storeys that are not public buildings — while a Senior Professional Engineer may work on all types and sizes. Having a Senior Professional Engineer sign therefore eliminates the problem of "signatures beyond the license scope," which causes drawings to be rejected and the whole set to be re-signed. Read the scope of each grade at Thai Engineer License Grades: What Can Associate, Professional and Senior Engineers Sign?
I already have drawings — can you just sign them?
Not in the sense of "signing without checking" — SPN engineers check and recalculate every set before signing. But if the existing drawings are already correct, the fee is for checking and certification, not for a new design. The reason is that the signatory is legally responsible for the safety of that structure under the Engineer Act B.E. 2542 (1999) and the COE code of ethics. Signing work one has not checked is an ethics violation, and a risk for the building owner too.
In practice there are 3 common cases
- Complete and correct drawings and calculations — the engineer reviews them, spot-checks the key calculations, then signs and issues a certificate. This is the fastest and lowest-cost case.
- Architectural drawings but no structural drawings or calculations — SPN prepares new structural drawings and calculations and then signs them. See the scope at Civil Engineering Design Services
- Completed structure with no drawings — requires a site survey, measuring structural member sizes, scanning for reinforcement and testing concrete strength as needed (rebar scan, UPV, rebound hammer or core test) before preparing as-built drawings and calculations for certification.
Which jobs most often need this service?
- House and building extensions — kitchen or carport extensions, adding a storey, or alterations that need a permit application with an engineer's signature. Read more at Foundation design for extensions
- Contractors and designers without an engineer of the grade required by law — work beyond the scope of an Associate Engineer, or public buildings
- Factories and warehouses — installing machinery on an existing floor, rooftop solar panels, storage racks (selective racks) or increasing floor live loads, where an engineer must certify that the existing structure can carry the load. See How much load can a warehouse floor carry
- Building sale, transfer or loans — banks, insurers or buyers requiring a certificate of structural soundness. See Pre-purchase building inspection
- Buildings after an event — earthquake, fire, flood or settlement, where an engineer must assess and certify the building before continued use. See Post-earthquake building inspection
What documents do you need to prepare?
The more complete the information, the more accurately and quickly the engineer can assess the scope and quote. Documents to have:
- Architectural and structural drawings (PDF/DWG files or photos of blueprints), if available
- Existing calculations, if available
- Photos of the actual structure from several angles, for completed buildings
- Soil investigation or pile test results for the project, if available (if not, SPN can carry out soil investigation and pile testing in the same job)
- The purpose and the agency you will submit to (district office/municipality/SAO, bank, industrial estate, employer), since each requires a different document format
- Copy of the title deed or land right document, and building owner details, to fill in the certificate
The 4-step process
- Send information and state the purpose — via LINE @spnth, email info@spnth.com or the contact form. An engineer replies with the scope of work and a quotation within 24 hours.
- Document review and site survey (when needed) — for existing buildings or jobs without drawings, the engineer visits the site, takes measurements and performs non-destructive structural testing as agreed in the quotation.
- Calculation and document preparation — check calculations or prepare new calculations to the standards referenced by the building control law (EIT standards and the relevant Ministerial Regulations), with revised or as-built drawings.
- Signing and delivery — drawings, calculations, certificate and a certified copy of the signing engineer's license are delivered as files and as original hard copies in the number of sets the agency requires.
How is the certification fee calculated?
There is no fixed standard fee, because it depends on whether the job is checking and certifying drawings that are already correct, preparing new calculations, or surveying and testing an existing building before certifying it. The main factors are the size and complexity of the structure, the completeness of the existing drawings and data, whether a site survey or structural testing is required, the number of document sets to be signed, and the distance to the site. SPN provides a free quotation within 24 hours of receiving the information. Fees involving a site survey exclude travel and equipment mobilization, which are charged extra according to the distance to the site. Read more about how design fees are structured at How structural design fees are calculated
Which areas do you serve?
Document review and certification can be done nationwide by sending information online. For jobs requiring a site survey, our engineering team travels from the office in Bang Sao Thong, Samut Prakan, regularly covering Bangkok and its vicinity, the East/EEC and Central Thailand, and takes jobs nationwide in all 77 provinces.