Foundation work for extension on existing buildings

A floor slab should be possible without any problems. But as mentioned, this should be checked by a structural engineer.

At our place, the exterior walls on the ground floor as well as in the basement are each 38 cm brick walls.

For a small house back then above standard – and accordingly heavy.

Whether you need underpinning I cannot tell you. We have one at the old retaining wall in the area of the house. It was determined back then by the structural engineer, expert, and the construction contractor.

Work was done in 1.5-meter increments. 1.5 m excavated and concreted, 3 m left standing, 1.5 m excavated, and so on. A few days later the next 1.5 m, and a few days later the rest. Roughly took about 2 weeks.