Technical Booklet N Drainage·Page 24·3.10
Drain protection where lower than building foundations – trench more than 1 m away
Where a drain is at a level lower than building foundations and the trench is more than 1 m from the foundations, the drain must be filled with concrete to a level below the foundation underside equal to the distance from the foundations less 150 mm.
(b) where the trench is more than 1 m from the foundations, be filled with concrete to a level, below the level of the underside of the foundations, equal to the distance from the foundations less 150 mm as shown in Diagram 3.7(b).
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