Prevent your house from sinking. Survey the land before deciding to buy.
Last updated: 3 Aug 2025
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No matter where you live, land subsidence is a common problem. However, the severity or extent of subsidence varies from person to person, as various factors affect each piece of land. If we're aware of the problem, we can still find solutions. However, if we don't inspect our land beforehand and build a house on it, then subsidence can have serious consequences for the structure of the house, resulting in significant costs and time for repairs. Today, we'd like to share some tips on how to inspect your land before building a house. Whether you're buying a house in a housing development, you can use this information to help you make your decision.
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1. Investigate the history of your land
Investigating the history here isn't a mystery. Instead, we should examine what the land was like before it became our farmland. If it was a rice paddy, a basin, a pond, or near a water source, even if you fill it in firmly, there's a high chance the land will subside. If you can change the situation, it's best to find a new plot of land. However, if the land is inherited, it's best to consider finding a new plot of land. Or if you truly cannot find any other location and must build a building on this dry land, you should carefully study methods for preventing soil subsidence. This includes compacting the soil, pile size, pile depth, and other structural work. This ensures that even if the soil subsides, your house can remain stable and not be damaged.
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2. Study Land Subsidence in Bangkok and the Metropolitan Area
Bangkok and the Metropolitan Area were once a sea over 10,000 years ago. The area is covered with soft, 8-12 meters thick clay (in some areas, much thicker) alternating with a layer of groundwater. The use of groundwater, the construction of tall buildings, and vibrations from road traffic have caused the soil to subside annually. This soft clay layer is unable to directly support the weight of the building. Therefore, pile driving is necessary to transfer the weight of the building to the stronger soil below. Houses typically have their piles placed at the tips of the hard clay or first layer of sand. Different zones of Bangkok experience varying degrees of land subsidence. The area experiencing the highest subsidence is in Bang Kapi District, with accumulated subsidence of approximately 1.20 meters. The least is on the Nonthaburi side. Even if your land has never been a rice paddy, a basin, a pond, or near a water source, if it's an area with significant subsidence, extra caution is required.
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3. Soil Not Firming Before Building Construction
Compacting the soil is a great way to prevent subsidence. Compacting the soil is especially effective. Each layer of soil should be 20-50 centimeters deep. Gradually compacting the soil layer will ensure a perfectly compacted area, ensuring safe construction without subsidence. However, it's not necessary to start building immediately after the soil is completely filled. Ideally, the soil should be left in the fill for 2-3 years, with no further subsidence observed before building. However, if you don't have enough time or want to start building quickly, it's best to wait until after the rainy season.
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4. Surrounding Forces
If our house is built next to a large construction site where piles are driven by a crane, the vibrations from the pile driving and the movement of the soil will cause the land around our house to shift. Our ceiling cornices may even come loose from the vibrations, cracks in the house itself, and even subsidence. Even houses located near excavated land for sale or large ponds may also experience subsidence.
___________________________________________
A house built with strong, stable, standard piles driven to the appropriate depth will remain stable even if the soil subsides. When building a house, never forget to consider these factors. If a problem arises, it is extremely difficult and expensive to fix. Even if you buy a house from a housing development, where you cannot know the structure of the house, at the very least you can survey the history of the land in that area to assess the risks and find preventative measures before problems arise.
___________________________________________
Thank you for the great information from HOMEDAY.
___________________________________________
1. Investigate the history of your land
Investigating the history here isn't a mystery. Instead, we should examine what the land was like before it became our farmland. If it was a rice paddy, a basin, a pond, or near a water source, even if you fill it in firmly, there's a high chance the land will subside. If you can change the situation, it's best to find a new plot of land. However, if the land is inherited, it's best to consider finding a new plot of land. Or if you truly cannot find any other location and must build a building on this dry land, you should carefully study methods for preventing soil subsidence. This includes compacting the soil, pile size, pile depth, and other structural work. This ensures that even if the soil subsides, your house can remain stable and not be damaged.
___________________________________________
2. Study Land Subsidence in Bangkok and the Metropolitan Area
Bangkok and the Metropolitan Area were once a sea over 10,000 years ago. The area is covered with soft, 8-12 meters thick clay (in some areas, much thicker) alternating with a layer of groundwater. The use of groundwater, the construction of tall buildings, and vibrations from road traffic have caused the soil to subside annually. This soft clay layer is unable to directly support the weight of the building. Therefore, pile driving is necessary to transfer the weight of the building to the stronger soil below. Houses typically have their piles placed at the tips of the hard clay or first layer of sand. Different zones of Bangkok experience varying degrees of land subsidence. The area experiencing the highest subsidence is in Bang Kapi District, with accumulated subsidence of approximately 1.20 meters. The least is on the Nonthaburi side. Even if your land has never been a rice paddy, a basin, a pond, or near a water source, if it's an area with significant subsidence, extra caution is required.
___________________________________________
3. Soil Not Firming Before Building Construction
Compacting the soil is a great way to prevent subsidence. Compacting the soil is especially effective. Each layer of soil should be 20-50 centimeters deep. Gradually compacting the soil layer will ensure a perfectly compacted area, ensuring safe construction without subsidence. However, it's not necessary to start building immediately after the soil is completely filled. Ideally, the soil should be left in the fill for 2-3 years, with no further subsidence observed before building. However, if you don't have enough time or want to start building quickly, it's best to wait until after the rainy season.
___________________________________________
4. Surrounding Forces
If our house is built next to a large construction site where piles are driven by a crane, the vibrations from the pile driving and the movement of the soil will cause the land around our house to shift. Our ceiling cornices may even come loose from the vibrations, cracks in the house itself, and even subsidence. Even houses located near excavated land for sale or large ponds may also experience subsidence.
___________________________________________
A house built with strong, stable, standard piles driven to the appropriate depth will remain stable even if the soil subsides. When building a house, never forget to consider these factors. If a problem arises, it is extremely difficult and expensive to fix. Even if you buy a house from a housing development, where you cannot know the structure of the house, at the very least you can survey the history of the land in that area to assess the risks and find preventative measures before problems arise.
___________________________________________
Thank you for the great information from HOMEDAY.
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