Vusumuzi Dube
Real Estate matters with Jonathan Thompson
IN a previous article I spoke about the different soil types that you might experience. Soil types in Zimbabwe can very from very sandy, to rock, to black cotton soils. Each soil type has a different rate at which the soil settles, and they also vary in their “bearing capacity”. Bearing capacity is how much weight can the soil support.
This is very important when deciding on a property’s suitability for construction, and for different construction types. A soil test can be done to determine a soil’s bearing capacity. One soil type may be suitable for a small structure, but not suitable for a large multi-level building. The soil type will also determine that type of foundation that can be approved.
The standard foundation in Zimbabwe is a brick foundation, that is laid in strips. These foundation strips will be underneath the brick walls of the house, both the internal and external walls. This is the easier and least expensive foundation that we commonly see utilised in Zimbabwe.
When the soil is made up of a high percentage of clay, it will have a tendency to “heave”. “Heaving” means that the ground will rise up, or heave, whenever it becomes moist. Therefore, in the rainy season the ground is higher.
When clay soil dries out, it shrinks, and becomes lower. This process of heaving can destroy a standard foundation. If you have gone into a home that has multiple cracks in the walls and floor, this was likely caused by heaving.
To fix this issue, after construction, you can attempt to strengthen the foundation with under pinning. Other people have added a cement skirting around the home to try and push incoming water further away from the foundations.
A house built on these types of soils needs to use a different foundation. Many people refer to these as “special foundations”. One type of special foundation is a raft foundation. This is a foundation of reinforced concrete. The foundation is one piece and the building sits on it, like a person sits on a raft. This raft foundation will carry the building during heave, similar to a raft riding on ocean waves.
The house will rise, shift, and fall without taking damage. This type of foundation is more expensive than a standard one.
Construction should not occur on made up ground, unsettled soils, collapsing subsoils, ant or termites’ nest, or over excavated areas. With areas like these, you may require a pile foundation. A pile foundation is made up of columns going down into the ground, beyond any trouble spots, to the solid rock below.
A structural engineer is needed with pile foundations. They will need to determine the number of piles, the distance apart, the depth, the materials, and more. Once the piles are formed under the ground, a ring beam of reinforced concrete is made.
The structure is then built on top of the ring beam. Pile foundations are very technical and costly, but are useful in areas where the soils are not suitable for construction.
Before embarking on your construction journey, it is essential to understand the soils and foundations that you will be dealing with. These two factors alone may greatly impact the type of building that you can construct, and the cost of your new home.
It may be easier to move to another property which already has the soils that are suitable for your dreams and plans.
Jonathan Thompson is a Registered Real Estate Agent who works in Bulawayo. He has nine years of experience in Real Estate in the USA, and another 11 years’ experience in Bulawayo. He is the founder and the Managing Director of Thompson Properties (Pvt) Ltd.
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derick.khumalo