The maximum area of vertical reinforcement should not exceed 4% of the gross cross sectional area of the concrete. Horizontal reinforcement equal to not less than half the area of vertical reinforcement should be provided between the vertical reinforcement and the wall surface on both faces.
The spacing of the vertical bars should not exceed the lesser of 300mm or twice the wall thickness. The spacing of horizontal bars should not exceed 300mm and the diameter should not be less than one-quarter of the vertical bars. If the vertical reinforcement exceeds 2% of the gross cross-sectional area of the concrete then links should be provided in accordance with EC2 - clause 5.5.6.