Clarification of TU21 requirement for dynamic watertightness testing

TU21 states that a dynamic watertightness test is required when the wind load exceeds 1800Pa. A query has been raised whether this is the positive wind load or the greater of the negative and positive pressures. TN95 Weathertightness of windows, doors and curtain walls refers to the positive wind load. It was agreed that as water penetration is most likely to be caused by positive wind load it would reasonable to base the requirement on the positive wind load.
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