Therefore,the foundation excavation should normally be at least to the same depth as the bottom (invert) of the deepest part of the drain, sewer or its trench.
Fel rheol, felly, dylai'r gwaith cloddio ar gyfer y sylfaen fynd o leiaf hyd at yr un dyfnder â gwaelod (wyneb mewnol isaf) rhan ddyfnaf y ddraen, y garthffos neu'i chwter.