Box Gutters

Box gutters must:

  • Be designed by a hydraulic engineer and verified by the MPX hydraulic engineer.
  • Filled and tested for 24 hours.
  • Be supported at:
  • Each stop-end
  • Either side of sumps
  • Either side of expansion joints
  • At rain heads
  • At generally not greater than 750 mm centres elsewhere
  • Be straight with no reduction in width or changes in direction.
  • Have a constant slope between 1:40 & 1:200 with no ponding except for water retained due to surface tension. Ponding result from any one of or a combination of the following, is a defect.
  • Have lapped joints made against the direction of flow.
  • Have expansion joints to be a proprietary EPDM rubber expansion joint.
  • Have expansion joints at the high point of the gutter.
  • Overhang of the roof sheeting must extend a minimum of 50 mm into the box gutter but never more than 200 mm.


  • Maintain a minimum of 300 mm between sheet ends to permit cleaning of the gutter.
  • Box gutter sumps must be fitted with overflow ducts, overflow channels or high capacity overflow devices
  • Box Gutter Sumps
  • Ensure that adequate overflow provisions are made, and any surcharge is accommodated
  • Have an overflow weir not less than 25 mm below the sole of the gutter discharging to the rain head.
  • Box gutters must be installed with sumps or rainheads
  • Overflows must discharge outside of the building in a visible location. This provides a visual warning that when running, indicates the stack our sump is choked.