Foundation work is one of the most important parts of construction for supporting a building’s safety and durability. If the foundation is inadequate, it can affect the strength and service life of the entire building. This article explains the role of foundation work, its main types, typical costs, the construction process, and key maintenance points.
What is the role of foundation work in a building?
Foundation work is the construction process that creates the structural base of a building. It plays an essential role in transferring the building’s weight to the ground and protecting the structure from earthquakes and ground settlement.
Three roles that foundation work fulfills
Foundations mainly serve three roles. First, they distribute the building’s load evenly to the ground. Second, they disperse earthquake movement and help prevent uneven settlement. Third, they protect the building from ground moisture and rainwater.
Foundations also have a service life
Even reinforced concrete foundations have a service life, generally estimated at around 30 to 60 years. Because rebuilding a foundation later is extremely difficult, initial construction quality and regular maintenance are both important.
What types of foundation work are there?
Foundation work is broadly divided into two categories: pile foundations and shallow foundations. The appropriate choice depends on ground conditions and the scale of the building.
What is a pile foundation?
This method is used when the ground is weak, with piles driven down to a deep bearing layer. It is often adopted for large buildings and is known for its high load-bearing capacity. Common methods include cast-in-place concrete piles and precast pile systems.
Shallow foundation: mat foundation
This method covers the entire bottom surface of the building with a concrete slab. Because it distributes the load over a wide area, it reduces the burden on the ground and also helps prevent moisture and termite intrusion. It is the most common method in current residential construction.
Shallow foundation: strip foundation
This method places concrete foundations only under the building perimeter and major partition walls. It generally costs less than a mat foundation, but its moisture resistance is lower.
Shallow foundation: isolated foundation
This method provides an independent foundation for each column and is mainly used in steel-frame buildings. It offers efficient construction, but it requires uniform ground conditions.
What is the typical cost of foundation work?
The cost of foundation work varies significantly depending on the construction method and the size of the building. It is important to understand the usual price range in advance.
Typical cost of a mat foundation
A general guideline is about 50,000 to 80,000 yen per tsubo. For a 30-tsubo house, that comes to roughly 1.5 million to 2.4 million yen.
Typical cost of a strip foundation
The typical cost is about 40,000 to 60,000 yen per tsubo, which is generally around 10% to 20% lower than a mat foundation.
Typical cost of a pile foundation
Costs vary widely depending on the number and length of the piles, but in many cases an additional 1 million to 3 million yen is required.
What is the construction process for foundation work?
Foundation work is the first step in building construction. It is helpful to understand the general process.
Ground investigation
First, the ground strength is investigated and an appropriate foundation method is selected. If the ground is soft, ground improvement work will be necessary.
Excavation and crushed stone bedding
The area where the foundation will be built is excavated, then crushed stone is spread and compacted. This is an important step for improving the overall stability of the foundation.
Rebar placement and formwork installation
Reinforcing bars are assembled and formwork is installed to pour the concrete. The accuracy of the rebar placement directly affects the strength of the foundation.
Concrete pouring and curing
Concrete is poured and given an appropriate curing period (generally about one week) so that it can develop sufficient strength.
What points should be checked when maintaining the foundation?
Finding and addressing foundation deterioration early helps extend the life of the building.
Check for cracks
Cracks wider than 0.3 mm are a sign of a structural issue. Carry out regular visual inspections, and if you find any, consult a specialist.
Check drainage and water runoff
If water collects around the foundation, deterioration will accelerate. Check drainage channels for blockages and the slope of the ground on a regular basis.
Termite prevention
Termites may enter through gaps in the foundation. Regular waterproofing and termite treatment are therefore important.
Frequently Asked Questions (FAQ)
Q. Which is better, a mat foundation or a strip foundation?
In current residential construction, mat foundations are the standard choice. Because they offer strong moisture protection and excellent seismic performance, they are generally selected unless there is a specific reason not to use them.
Q. How long does foundation work take?
For a typical detached house, it usually takes about two to four weeks. If ground improvement is required, an additional one to two weeks is often needed.
Q. Can foundation cracks be repaired?
Minor cracks can be repaired by injecting epoxy resin. In the case of serious structural cracks, specialized reinforcement work will be necessary.
