In building terms the oversite refers to a layer of concrete that is used to seal the earth and create the ground floor of your house.
Concrete oversite floor.
So placed to prevent disturbance of the ground below to provide a relatively even and firm surface for the placement of the next layer and to keep out ground air and moisture.
Like everything it is a very important step as it is what you will be essentially walking on when the extension is built.
An underlayer of concrete below a slab or other flooring.
From the early part of the twentieth century it became accepted practice to cover the site of buildings with a layer of concrete some 100 mm thick the concrete oversite or oversite concrete.
As nouns the difference between oversite and oversight is that oversite is a flat solid layer of concrete serving as a base for flooring while oversight is an omission.
Something that is left out missed or forgotten.
The floor is made up of precast concrete beams shaped a bit like the rails on a train track.
At the time many ground floors of houses were formed as raised timber floors on oversite concrete with the space below the floor ventilated against.