Technical Booklet N Drainage·Page 24·3.10
Drain protection where lower than building foundations – trench within 1 m
Where a drain is at a level lower than building foundations and the trench is within 1 m of the foundations, the drain must be filled with concrete up to the level of the underside of the foundations.
A drain which is at a level lower than the foundations of a building should either – (a) where the trench is within 1 m of the foundations, be filled with concrete up to the level of the underside of the foundations as shown in Diagram 3.7(a); or
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