What Actually Changed in May 2025
The governing instrument is a Notification of the Ministry of Natural Resources and Environment designating environmental protection areas and measures for the sub-districts of Taling Ngam, Bo Phut, Maret, Mae Nam, Na Mueang, Ang Thong and Lipa Noi in Koh Samui District, together with Koh Phangan, Ban Tai and Koh Tao sub-districts in Koh Phangan District, Surat Thani, B.E. 2568 (2025).
Three points about its legal character matter more than they might appear to.
- It is a Notification, not a Ministerial Regulation. The Minister issued it under section 45 of the Enhancement and Conservation of National Environmental Quality Act B.E. 2535 (1992), following approval by the National Environment Board and the Cabinet.
- It took effect on 22 May 2025, not 21 May. The Royal Gazette published it on 21 May 2025, at Volume 142, Special Part 199 Ngor. The notification then applies from the day after publication. That single day decides which buildings are grandfathered.
- It expires on 21 May 2030. Section 45 gives instruments of this type a five-year life. The previous notification, dated 8 May 2014, was extended three times before this one replaced it outright.
The Seven Zones
The notification divides the protected territory into seven areas. Getting the zone right is the first step in any site assessment, because the restrictions differ sharply between them.
| Zone | What it covers |
|---|---|
| 1 | Marine waters surrounding Samui and Phangan, within a defined polygon. |
| 2 | All land from the shoreline inland on Koh Samui, Ko Taen and Koh Phangan, except land falling in Zone 3. This is the whole island below 80 metres, not merely the coastal strip. |
| 3 | Elevation bands. Zone 3(1) covers 80 to 140 metres above mean sea level on Samui and Phangan. Zone 3(2) covers everything above 140 metres. Zone 3(3) covers land above 80 metres on Ko Taen. |
| 4 | The entire land area of roughly eleven named small islands. |
| 5 | The entire land area of roughly twelve named islets. |
| 6 | Further named islets, plus any island inside Zone 1 waters not already listed. |
| 7 | Koh Tao and Koh Nang Yuan, plus the marine waters around Koh Tao. Koh Tao has its own regime and is materially lighter than Samui or Phangan. |
Two of these assignments are routinely reported wrongly. Koh Tao sits in Zone 7, not in Zones 2 and 3. Zone 2 is not “beachfront land”; it is all land below the 80-metre contour.
What the Koh Samui Building Regulations Let You Build
The hillside rules are the ones that reshape a project. Zone 3 begins with a general prohibition on construction, alteration and change of use. It then carves out narrow exceptions on privately owned land.
- Zone 3(1) and 3(3), from 80 to 140 metres. A single detached house only. Height must not exceed 6 metres. At least 50% of the plot stays open. At least half of that open space must be green, planted principally with perennial trees. The roof must be pitched in a Thai or tropical style and cover at least 80% of the building area. Natural colours apply: brick, terracotta, brown, grey or leaf green.
- Zone 3(2), above 140 metres. The same rules apply, except that at least 70% of the plot must remain open.
- Zone 4. Buildings must sit at least 10 metres back from the shoreline. Height is capped at 6 metres, total area at 75 square metres, and 75% of the plot must stay open.
- Zone 5. The notification prohibits buildings except for public benefit or state agency works, and even then caps height at 3 metres.
- Zone 6. The notification prohibits all buildings of every type, apart from structures serving navigation safety.
In Zone 2, hotels and multi-unit residential buildings must keep at least half of their statutory open space as green area. Notice how that rule works. It takes a percentage of the open space that the Building Control Act or town planning law already requires, so it stacks on top of those regimes rather than replacing them.
Slope Rules Under the Koh Samui Building Regulations
Sea views on both islands come from gradient, and gradient is precisely what the notification restricts.
Where the slope reaches 35% or more, across Zones 2 to 4, only single detached houses qualify, and height stops at 6 metres. On plots larger than 100 square wah, the footprint must not exceed 90 square metres, and at least 70% of the plot must stay permeable. On smaller plots the footprint drops to 70 square metres.
Earthworks face limits too, and they bite hard on view lots. On slopes of 35% or more, regrading must not exceed a ratio of three horizontal to one vertical. No cut or fill may go deeper or higher than one metre from original ground level, foundations and underground tanks excepted. At 50% slope, a further rule bites. You may not damage the trunk or root system of any naturally occurring tree with a girth of 50 centimetres or more, measured at 1.3 metres.
Three Regimes, and the Strictest Wins
This is the point that causes the most expensive mistakes. A Samui or Phangan project must satisfy three separate bodies of law at once.
- The Building Control Act B.E. 2522 and the local ordinance. The familiar 12-metre height limit, the 200-metre coastal band and the 2,000-square-metre cap come from the Koh Samui Municipal Ordinance B.E. 2560. They do not come from the environmental notification. They sit under a separate statute and remain fully in force.
- Town planning law. Land use zoning operates independently and continues to apply.
- The environmental notification. The measures described above.
The notification resolves the overlap expressly. Where another law prescribes an environmental protection measure that is not lower than, or is better than, the measures in the notification, that other law governs. In practice, therefore, each parameter is set by whichever regime is strictest. Enforcement runs through the same building control officials who handle permits. The three regimes therefore converge at one counter.
When an Environmental Study Is Required
The notification sets two tiers, and they are frequently reported as one.
- Initial environmental evaluation. This covers hotels and condominiums more than 50 metres from the shoreline with 50 to 79 rooms, or floor area between 2,500 and under 4,000 square metres. Land subdivisions of 100 to under 500 plots, or 19 to 100 rai, also fall here.
- Full environmental impact assessment. Hotels and condominiums with 80 rooms or more, or 4,000 square metres or more. Critically, any hotel or condominium within 50 metres of the shoreline requires a full assessment regardless of its size.
The widely repeated claim that a full assessment is triggered at 50 rooms or 2,500 square metres is wrong. That band is the initial evaluation threshold. Confusing the two understates the cost and timeline of a coastal project considerably.
Smaller projects are not exempt either. Hotels and multi-unit buildings with 11 to 49 rooms must meet annexed construction and operating requirements. Those cover drainage control, dust screening, a solid boundary fence of at least 2 metres, daytime-only noisy work, and annual water quality reporting to the provincial office.
Correcting the Numbers in Circulation
The notification runs to twenty pages, in Thai, as a scanned document. Most English summaries therefore rely on secondary sources, and several errors have spread widely. Before relying on any figure, check it against this list.
| Commonly stated | Actual position |
|---|---|
| Effective 21 May 2025 | Effective 22 May 2025, the day after publication |
| Elevation bands at 50 m and 150 m | 80 m and 140 m |
| Koh Tao sits in Zones 2 and 3 | Koh Tao is Zone 7, under a lighter regime |
| Zone 2 means beachfront land | Zone 2 is all land below 80 m |
| Full assessment at 50 rooms or 2,500 sqm | That is the initial evaluation band; full assessment starts at 80 rooms or 4,000 sqm |
| Building banned on slopes above 50% | Draft provision, not enacted; tree protection applies instead |
| No construction within 10 m of any shoreline | The 10 m setback applies in Zones 4 and 5 only |
| 12 m height and 2,000 sqm cap come from this law | Those come from the Koh Samui Municipal Ordinance under the Building Control Act |
Where a seller, agent or contractor quotes a rule, ask which instrument it comes from. If the answer is vague, treat the figure as unverified. Our note on what to do when a contractor abandons a villa project shows how quickly a permitting defect becomes a construction dispute.
What Buyers and Developers Should Do Now
- Establish the zone and the contour before you offer. Commission a survey rather than relying on a seller’s plan, and read it alongside our guidance on buying and selling land in Thailand as a foreigner. Elevation and slope decide value here more than plot size does. A parcel straddling the 80-metre line is really two different assets.
- Check the grandfathering date. The notification treats buildings existing on or before 22 May 2025 differently from later work. Verify what actually stood on that date, not what the permit allowed.
- Do not assume a permit ends the enquiry. Officials issue permits under the Building Control Act. Compliance with the environmental notification is a separate question, and the strictest rule governs.
- Model the 2030 expiry. For a development with a long build and hold period, the applicable regime may be remade mid-project.
- Rental plans need their own analysis. Room counts drive the environmental thresholds and the licensing position alike. Our guide to the hotel licence for rental villas covers that side.
Frequently Asked Questions
When did the current Koh Samui building regulations take effect?
What is the height limit for a hillside villa on Koh Samui?
Do the same rules apply on Koh Phangan and Koh Tao?
Is building prohibited on steep land?
Does a building permit mean the project complies?
Conclusion
The Koh Samui building regulations are no longer a single set of rules a local contractor can recite from memory. They are three overlapping regimes. One of them changed in May 2025 and expires in 2030, and the English-language summaries in circulation contain errors on almost every material figure. On islands where a single sea-view parcel can carry a nine-figure baht price, verifying the instrument behind each number is not a formality.
Related reading: zoning is only half the picture. See our analysis of the 30-year lease in Thailand and the renewal trap, and of buying a villa in Thailand that is held inside a Thai company.
Buying or Building on Samui or Phangan?
Lex Bangkok advises international buyers, developers and investors on island land acquisition, zoning and environmental compliance, permitting and construction disputes. We work from the instruments themselves, not from summaries, and we tell you what a parcel can carry before you commit to it.
Request a Site and Title ReviewThis article provides general information on Thai law and does not constitute legal advice. Zoning, elevation and slope determinations are parcel-specific and require survey evidence. Obtain advice on your own site before acting. The notification is published in the Royal Gazette, and environmental protection area policy is administered by the Office of Natural Resources and Environmental Policy and Planning.