"Is hiring a structural design engineer expensive?" is one of the first questions homeowners and contractors ask when they are about to apply for a building permit. The straight answer: the design fee is usually a very small share of the total construction value, yet it is the money that decides both the safety and the economy of the structure. This article walks through how fees are priced, what you receive, and how to compare quotations properly.
How are structural design fees priced?
Structural design fees in the market are priced in 3 main ways: per square meter of usable floor area, as a percentage of construction value, or as a lump sum for the whole job. Each suits a different size of project, and all deliver the same document set: structural engineering drawings with calculations and the engineer's certification.
- Per square meter (THB/m²): Common for houses and small buildings. Based on the total usable floor area of all stories; easy to understand and straightforward to compare between designers.
- Percentage of construction value: Common for commercial buildings, factories and high-rises because it better reflects the complexity of the work. The percentage generally decreases as project value increases.
- Lump sum: Used for clearly defined scopes such as standard designs, small extensions or localized design revisions. One agreed price; the scope and the number of revision rounds should be stated clearly in the contract.
To give a rough picture: for work priced as a percentage of construction value, structural design fees in the market are typically around 1–3% of construction value (the larger the project, the lower the percentage). In relative terms, ordinary houses sit at the 💰 level, commercial buildings/factories at 💰💰, and high-rises or special structures at 💰💰💰 — these figures are market reference ranges only. Actual prices depend on the scope, complexity and conditions of each project; please contact us for a quotation based on your actual scope.
Whichever method is used, what should be agreed clearly from the start is the scope (structure only, or including architecture/MEP), the number of revision rounds, and the documents to be delivered — these three points are why quotations with different figures cannot be compared directly.
Which pricing method is common for each type of project?
Houses and small buildings are usually priced per square meter of usable floor area, while medium to large buildings are usually priced as a percentage of construction value. The table below summarizes common practice as a starting point for comparing quotations.
← Scroll to see the full table →
| Type of work | Common pricing method | How the price is agreed |
|---|---|---|
| Houses ≤ 4 stories | Per m² | Based on total usable floor area of all stories; rate depends on design complexity |
| Extensions / localized design revisions | Lump sum | Agreed case by case according to scope |
| Commercial buildings / factories / high-rises | % of construction value | Percentage falls as project value rises; agreed according to service scope |
The methods above are general market practice, not SPN's service rates — actual prices depend on the site, design complexity and the scope included. Ask designers or contractors directly.
Another common confusion is the "design" price versus the "construction" price — a construction quotation prepared from actual drawings with a bill of quantities (BOQ) is far more accurate than a rough per-square-meter estimate, which can vary widely. Investing in a complete design therefore also helps control the overall construction budget.
What do you get for the design fee?
The structural design fee covers 3 main groups of documents: structural engineering construction drawings, structural calculations, and the certification documents of the design engineer — the document set used to apply for a building permit with the relevant authorities, and for contractors to price and build the work.
- Structural engineering drawings (CAD/PDF files): Foundation, column, beam and slab plans, reinforcement details and connection details — complete enough for the contractor to build without guessing.
- Structural calculations: Documents showing the calculation of loads, material strengths and safety checks of members — buildings that fall under controlled engineering work (e.g. floor area over 150 m² under the Ministerial Regulation Prescribing Engineering Disciplines and Controlled Engineering Disciplines B.E. 2550 (2007), issued under the Engineer Act B.E. 2542 (1999)) must have a responsible engineer and attach the calculations when applying for a permit.
- Engineer's certification: The signature and professional license (COE) registration number of the design engineer, with a copy of the license, used to support the building permit application.
What each firm includes varies — some include architectural and MEP drawings, some include cost estimating (BOQ) or unlimited revision rounds. Before comparing prices, always make sure you are comparing the same "deliverables". For an overview of the full design scope, read Guide to RC Structural Design and Civil Engineering
Hiring an engineer to certify drawings prepared by someone else is not a money-saving shortcut: the signing engineer is accountable under the Council of Engineers regulations, so they must still review and recalculate before signing. This kind of work therefore costs and takes about as long as a new design, and drawings with no responsible engineer from the outset risk major revisions.
What factors make design fees differ?
Two houses with the same usable floor area can have very different design fees, because the price reflects the amount of calculation work and the engineer's responsibility. The main factors that make prices differ are:
- Building height and type: The taller the building or the wider the column spans, the more complex the structural analysis. Public buildings and factories have additional requirements beyond houses.
- Soil conditions and foundation system: Soft-ground areas such as Bangkok and its vicinity require pile foundations designed from soil investigation results, which involves more calculation than spread footings on stiff ground.
- Seismic requirements: Buildings in areas controlled by the seismic-resistance law must be designed for additional lateral forces, which increases the design workload.
- Architectural complexity: Offset plans, long cantilevers, multi-story voids or special structures take more design time than a regular column grid.
- Scope included: Structure only, or including architecture, MEP, BOQ and the number of revision rounds — the more included, the higher the price, but the more complete the package.
Besides the design fee, should you budget for a soil investigation?
Yes — soil investigation results are the baseline data the engineer uses to design the foundation, especially for houses that must have structural calculations. Designing a foundation without actual soil data forces the engineer either to add excessive safety margins (inflating the construction budget) or to risk choosing the wrong foundation system (settlement and cracking later). The soil boring fee is therefore a budget item that goes hand in hand with the design fee, not a luxury.
SPN's soil investigation fee for houses starts at approximately THB 20,000–40,000 (2–3 boreholes, including basic lab tests and a report certified by an engineer). This price excludes travel and equipment mobilization, which are charged extra according to the distance to the site. See service details at Soil investigation and testing or read the detailed price breakdown in Soil Boring Prices 2026
This article explains pricing principles to support budget planning only; it is not a quotation. Actual design prices depend on the site and the scope of each project — ask designers or contractors directly. For SPN's soil investigation prices, contact us for a free quotation within 24 hours.