Image of someone constructing a soakaway used to explain the cost of building a soakaway in Nigeria.

Cost of Soakaway in Nigeria: [Septic Tank Construction Method]


An idea of the cost of building a soakaway in Nigeria is vital if you have an ongoing building construction project in the country.

A septic tank and soakaway pit are inevitable in any house construction project, this is simply because the liquid and solid waste collected from the building with plumbing pipes are emptied into these important drainage systems.

Therefore knowing the functions and costs of these drainage structures will help you to follow up on your project during their construction and also help you to make a proper budget at this stage of your building project.

In this post, we shall look at the estimated cost of building a soakaway pit and septic tank in Nigeria by outlining the costs of materials and labor involved in their construction.

Furthermore, we shall see the functions of each of these systems, the difference between a septic tank and a soakaway pit, and an overview of the sizes of these drainage structures.

Before delving into details on the cost of soak away, let’s first define some terms associated with this structure.

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What is a Soakaway Pit?

A soakaway is simply a drainage pit designed to allow water to permeate into the ground beneath, in simple terms it allows wastewater to soak into the ground or soil.

In house construction in Nigeria, the walls of a soakaway pit are built with blocks for safety purposes, and its bottom is partially floored with concrete. The area at the bottom that is not concreted is where the water filters into the ground.

This structure collects wastewater from kitchens, baths, and showers.

What is a Septic Tank?

In the Nigerian context, a septic tank is an underground structure used to collect solid waste (basically feces) from houses, the structure houses the waste until it is time for disposal.

The walls of the septic tank are built with masonry blocks and its bottom is completely floored with concrete so that no waste escapes the container until sewage companies dispose of it.

However, the tank is constructed to have an air inlet on its top to allow oxygen into the container which will encourage bacteria to react to the feces, this bacteria activity will cause the tank to be slow in getting filled up by solid wastes.

  • Quick Note:

The soakaway and septic tank are commonly constructed together in Nigeria with a partition wall dividing the two drainage systems, the term soakaway is a common word used by Nigerians to refer to both systems.

However, depending on your choice, you can still build them separately, while the soakaway collects the liquid waste from baths and kitchen sinks, the septic tank will collect the solid waste from toilets or WC.

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Cost of Building Soakaway and Septic Tank in Nigeria

The cost of building a soakaway in Nigeria ranges from 400,000 naira to 750,000 naira and this amount includes the cost of digging the pit, the cost of materials, and the labor cost, and these costs will ultimately depend on the size of the system and the nature of the soil.

Let us now look at the building materials needed to build a soakaway in Nigeria and also the different labor works involved in the construction process, to help you make a proper budget for the construction of the structure.

Cost of Materials For Building a Soakaway in Nigeria

The following estimated quantity of materials (with prices) will be needed in the construction of a normal-sized soakaway and septic tank.

  • Cement – 13 bags @ 5,000 naira = 65,000 naira
  • Sharp sand – 1 strip @ 30,000 naira = 30,000 naira
  • Sand gravel – 1 strip @ 30,000 naira = 30,000 naira
  • Nail – 1 bag @ 15,000 naira = 15,000 naira
  • Block – 230 @ 350 naira = 80,500 naira
  • 10mm rod – 10 lengths @ 3,600 naira = 36,000 naira
  • Binding wire – 20kg @ 15,000 naira = 300,000 naira
  • Quater rod – 1 bundle @ 20,000 naira = 20,000 naira
  • Board – 15 lengths @ 2000 naira = 30,000 naira

From our analysis above, the estimated cost of materials for building a standard soakaway in Nigeria will be from 500,000 naira to 600,000 naira.

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Image of a soakaway under construction used to explain the cost of building a soakaway in Nigeria.
Soakaway under construction

Cost of Labor for Building a Soakaway in Nigeria

The following labor jobs are required while building a soakaway in Nigeria, the labor cost will be determined by what the laborers will charge while doing the jobs.

  • Soakway digging
  • Concrete works
  • Ironworks
  • Carpentry work
  • Plastering works

Based on my experience in the Nigerian building industry, the cost of labor of building a standard soakaway and septic tank ranges from 150,000 naira to 300,000 naira including the contractor’s fee.

Difference Between Soakaway Pit and Septic Tank in Nigeria

In the Nigerian context, the main difference between a soakaway pit and a septic tank is that the soakaway primarily collects liquid wastes from houses. In contrast, the septic tank collects solid wastes.

The soakaway receives the liquid wastes from kitchen sinks, wash basins, showers, etc through plumbing pipes and because its bottom is not entirely floored with concrete, the water filters into the ground causing the pit not to be filled up with the waste.

On the other hand, the septic tank receives solid waste from toilets or WCs, and it is constructed to store the waste until it is time to evacuate it.

As stated earlier, the oxygen that enters the tank from the air inlet helps to break down the waste through bacteria reactions, and this makes the septic tank not get full easily.

Moreover, in Nigeria, most homeowners prefer to construct the two drainage systems as one structure hence the laymen refer to both as soakaway.

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What is The Standard Size of Soakaway in Nigeria

The size of the soakaway drain you will use in your house will depend on the number of people expected to use the convenience in the house, and also on the nature of the soil where the underground structure will be sited.

In the Architectural design or mechanical drawing of your house, a document known as the ‘septic tank and soakaway pit details’ is included to detail the length, width, and depth of the drainage system you should construct.

The design and details of the soakaway as contained in the mechanical drawing are based on the expected number of users, the porosity of the soil in your site, and the setbacks from the fence to the drainage structure.

However, for a normal-sized house on good soil, the size of the soakaway pit and septic tank can be constructed as follows:

Drainage SystemLengthWidthDepth
Septic tank & soakaway (combined)9ft to 10ft4ft to 5ft7ft to 8ft
Septic tank5f to 6ft4ft7ft to 9ft
Soakaway pit4ft to 5ft4ft7ft
soakaway sizes

How To Construct Soakaway and Septic Tank in Nigeria

Construction workers should carry out the construction of a soakaway drainage system under the supervision of a builder or building expert, and the following are the steps involved in building this drainage system in Nigeria.

  • Setting Out of the Soakaway:

This is the process of mapping out the area where the soakaway will be sited, and this should be done by your builder based on the dimensions of the drainage system.

  • Digging of the Soakaway:

This is the process of excavating the area on the ground where the drainage structure is to be sited, the depth of the excavation is determined by the nature of the soil and the number of people expected to use the soakaway.

  • Floor concreting:

At this stage, the bottom of the septic tank is floored with concrete and the soakaway pit bottom is partially floored, the area of the soakaway bottom without concrete flooring is where water filters to the ground beneath.

  • Blocks works:

At this stage, the walls of the drainage system are constructed with blocks, and a demarcation wall is used to separate the septic tank from the soakaway pit.

  • Construction of columns and beams:

This is the stage where reinforced concrete columns and beams are added to the drainage system to strengthen it and prevent it from collapsing with time.

  • Top covering:

In this last stage of soakaway construction, its top is covered with a reinforced concrete slap, a manhole is provided on the slab covering to serve as entry and exit space for the servicing of the drainage system.

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Conclusion

The cost of construction of your soakaway drainage system will depend on its overall size and the nature of the soil, and the method of its construction should be determined by a construction expert based on the situation of your site.

If your house is a bungalow or a normal duplex, you may not need to dig too deep while building the system to reduce cost and for the safety of the drainage.

However, if you want a very deep soakaway, make sure that all necessary construction measures are employed by your building engineer during the construction process.

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