NHBC requirements for trench fill foundations.

Required when trees influence the depth of the foundation beyond 1.5m to a maximum of 2.5m deep.

Trench walls are vertical and corners are accurately formed.

Shuttering may be required to achieve this.

Compressible heave precaution pinned to the trench wall and corners neatly formed.

NHBC requirements for pile and beam foundation.

Required when foundations are in shrinkable soils and within the zone of influence of trees.

Area directly below the beam prepared with concrete blinding formed level.

Correct size heave precaution laid accurately to a line and continuous.

Ring beam heave precaution neatly cut around pile cap.

Check design for pile cap projection beyond the heave precaution.

Typically between 25mm and 75mm.

Refer to plot specific design.

Heave precaution is to be placed on the inside face of the external wall of the ring beam form work.