On Foundations: It is Safer to Pad the Strip
Foundations are very important components of buildings and other earth-supported structures because they perform what is often described as the most herculean tasks of support, transmissions and distribution –they support the load of the structure built on them and extensively transmit and distribute same to the underlying earth. There is always a set of suitable foundation types for most structures but these options are often subjected to cost consideration, time of completion and available technology. Generally for small residential bungalows on fairly stable earth, the use of traditional strip foundation is common place but technically it is safer and wiser to also pad the strip.
Here is why? Padding a strip foundation makes it stronger and more stable. It provides additional support against deflection. If properly constructed, it also gives the foundation a form of flexibility to take on additional load in the future which may be in form of an additional floor. Similarly, it enables ease of lateral extension. What this means in ordinary terms is that the pad in the strip will make it a lot safer to extend the foundation where the building’s horizontal span(s) is to be increased.
The combination of strip and pad foundation is logical to the extent that the bulk of the load of the building will be supported by the pad set-up, hence the strip only serve to sustain and distribute the load from the walls over the longitudinal bearing throughout its length. This is quite different from the norm where reinforcement is simple introduced at joints in foundation strip and concreted together. When applying this method, the required number of isolated or combined pad footings or base are first constructed over a layer of blinding and are then connected to the strip which could be made either of reinforced concrete or Sandcrete blocks or composite materials. Subsequently, the starter columns are built into the pad which will then be extended to the roof beams. This way the load from the roof is almost exclusively supported by the pad.
It works in such a way that the roof load is supported by the pad while the load from the wall and part of the ground floor is supported by the strip. This is generally safer and particularly useful in grounds with fairly-stable soil characteristics.
Engr. Osaz’ ENOBAKHARE is an award-winning Contractor, Structural Engineer and the CEO of Heavens Contractors Ltd. He is involved in design and construction of buildings, roads and infrastructure projects across Nigeria.