Both of these solutions depending on the soil conditions, footing and foundation of adjacent buildings, budget, timing and sewage system height, so highly recommended to have it done under the supervision of structural engineer.
These days, one of the common questions is how to raise/increase the height of basement floor (in new or old houses); The most popular and high-demand solution is to do Underpinning.
A very simple explanation about it is: A solid concrete foundation to be poured below the existing building to support and strengthen the building in order to raise the existing ceiling height of basement.
This method involves the following stages:
On the other hand, the Bench-Footing, also the same as Underpinning will strength the existing foundation wall; It makes less living space area but it is time saving and economical option in renovation projects.
In this technique, do not need to excavate below the existing footing to achieve more ceiling height.
Here is the process of Bench-Footing (Benching):
After these steps, you can start preparing and pouring the new concrete slab floor and then start wood/steel framing.
Please note where the foundation of building that going to be constructed is below level of the adjacent building footing and within the Angle of Repose (also known as critical angle of repose of a granular material which is the sharpest and the most vertiginous angle of dip that material can be piled without slumping, so at this angle, the material on the slope-face is on the border of sliding), so, do not disturb ground around this area.
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