When people talk about "designing a house or building", many think only of the architectural design that defines its appearance and usable space. But behind every building there is another side of design that is invisible yet just as important: civil and structural engineering design, which determines whether the building will be strong, safe and able to obtain a building permit. This article gives the full picture, from the scope of work, process, and standards and laws to how to choose a designer.
What does civil engineering design cover?
Civil engineering design is the engineering calculation and preparation of construction drawings, divided into 4 main groups: structural design, drainage systems, roads and site planning, and construction supervision, all of which must be the responsibility of a civil engineer holding a professional engineering license (COE) from the Council of Engineers Thailand.
- Structural design: calculating the size of foundations, columns, beams, slabs and reinforcement of RC or steel buildings so that they carry loads safely
- Drainage design: designing drainage channels, pipes and manholes to carry stormwater off the project site without ponding
- Roads & site plan: designing internal roads, parking areas, fill levels and the layout of buildings on the site plan
- Construction supervision: checking that the contractor builds in accordance with the drawings and standards, and resolving site issues
What is RC structural design, and how does it differ from an architect's work?
RC (reinforced concrete) structural design is the calculation and sizing of a building's load-bearing members — foundations, columns, beams and slabs — including the amount and placement of reinforcement, so that the building is safe under the applicable standards and laws. The output is a set of structural engineering drawings with a structural calculation report used to support the building permit application.
This work is clearly different from an architect's — the architect designs "what the building looks like and how it is used", while the structural engineer answers "what kind of structure will let that building stand safely". The two work side by side on the same set of drawings.
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| Topic | Architect | Structural engineer |
|---|---|---|
| Main concern | Usable space, form, aesthetics | Strength, safety, load-carrying |
| Deliverables | Architectural drawings (plans, elevations, sections, materials) | Structural drawings + calculation report |
| License | Architect (Architect Council of Thailand) | Licensed civil engineer (Council of Engineers Thailand) |
| Examples of what they specify | Room sizes, door and window positions | Column and beam sizes, reinforcement, foundation type |
A typical building permit application requires both architectural drawings and structural engineering drawings. In general, a house with more than 150 m² of usable floor area must also include a structural calculation report signed by a licensed engineer. Read the summary of the relevant foundation law in Summary of the 2023 (B.E. 2566) Ministerial Regulation on foundations
What does the design process look like? From soil investigation to signed drawings
Sound engineering design does not start with drafting; it starts with real data about the land. The typical sequence of steps is as follows:
- Soil investigation (soil boring): collect data on the soil layers, bearing capacity and groundwater level at the actual construction location, because foundations must be designed from real soil, not assumed values. See details in SPN soil investigation services
- Define the layout and building loads: take the architectural drawings and assess the dead loads, live loads and other forces such as wind and earthquake loads for the area
- Structural calculation: select the foundation system (spread footings or piles), then size the columns, beams, slabs and reinforcement to the standards
- Prepare construction drawings: produce the structural engineering drawings and other supporting drawings, such as drainage and site plans, in a form the contractor can build from
- Prepare the calculation report and sign off: a licensed engineer (COE) signs the drawings and calculation report for submission with the permit application to the relevant authority
The foundation is the one element you cannot design with a safety margin based on guesswork — without knowing the actual soil bearing capacity, the engineer must either assume very conservative values and waste money, or take on too much risk and end up with settlement and cracking. SPN soil investigation for residential houses starts from about 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 costs, which are charged extra according to the site distance. Read more on interpreting soil data in What is soil bearing capacity?
Which standards and laws must design work reference?
Structural and civil design work in Thailand falls under a number of laws and engineering standards. This table summarizes the main ones that project owners should know.
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| Law / standard | What it covers |
|---|---|
| Building Control Act B.E. 2522 (1979) | The principal law governing permits to construct, modify and demolish buildings, and the Ministerial Regulations issued under it |
| Ministerial Regulation on Building Foundations and Supporting Ground B.E. 2566 (2023) | Criteria for the load capacity of foundations and ground, which give soil investigation data a direct role in design |
| Ministerial Regulation on Earthquake Resistance B.E. 2564 (2021) | Defines the areas and building types that must be designed to resist earthquakes |
| DPT 1301/1302-61 | Standard for the seismic-resistant design of buildings, issued by the Department of Public Works and Town & Country Planning |
| EIT standards | Design standards for RC and steel structures by the Engineering Institute of Thailand, which engineers reference in their calculations |
| Council of Engineers regulations (COE) | Specify which types of design work must be performed by which grade of engineer, and the sign-off of drawings and calculation reports |
Home or project owners do not need to know every detail of each document, but they should check that the designer references these standards in the calculation report and that it is signed by a genuinely licensed engineer.
How do you choose a reliable design engineer?
A good designer is not judged by the lowest price, but by the reliability of the work and the documents delivered. Basic criteria to consider include:
- Holds a professional engineering license (COE): the name and registration number can be verified with the Council of Engineers, and the license grade must suit the size of the building being designed
- Has experience with similar work: has designed buildings of a similar type and size to your project, such as houses, factories or high-rise buildings
- Delivers complete documents: structural engineering drawings, calculation report and signed certification documents — not just the drawings alone
- Communicates and revises: explains the design rationale so the project owner understands, with clear terms for design revisions
On cost, structural design for typical houses is usually charged per square meter of usable floor area, while large buildings are usually charged as a percentage of the construction value. Actual prices depend on the site and the scope of work, so request a quotation directly from the designer. Read an in-depth explanation of how fees are calculated in How RC structural design fees are calculated
The content of this article is general educational information, not design advice for any particular project. The size of the foundations, columns, beams and reinforcement for each building must be calculated by the responsible engineer from the project's actual data, especially the soil investigation results at the construction location.