ACO New Zealand




Hydraulic performance of building threshold drains can be split into two issues for consideration.

  1. Grating performance—i.e. will the grate chosen perform adequately to capture all the water that the drainage channel is installed to intercept? Grate performance is determined by the hole sizes, orientation and quantity. If the grate of the chosen width is not adequate, there will possibly be water bypass which may enter the building creating damage. In the instance of a grate not being able to handle the water catchment, a wider grate (and channel) can be used to ensure total capture. Performance of the grate intake can be compromised by the slope of the pavement towards the channel (excessive slope can create higher velocity of approaching water) and if the grate has to catch façade run off this needs to be taken into account. Contact ACO for information on grate intake performance.
  2. Channel performance—Is the channel under the grate sized sufficiently to carry the captured water to the outlet pipe for discharge into the storm water sewer/soak away? If the grate intake capacity is too great for the channel, flooding will occur along the channel run. Sizing of channels (width and depth) is important to a correctly sized channel drain. Avoidance of flooding is important with building threshold drainage as water build up in the channel can both cause flooding in the building interior and damage to foundations, wall structures and building facia’s. Adding slope to channels improves evacuation performance, and correct sizing, and positioning, of outlet pipes is important to channel performance. Contact ACO for information on correct sizing of channel bodies.

Note: In the case of Profi-Line green roof drainage the channel is designed to remove volumes of water from the surface which enter the channel through the grate, the perforations in the body allow water running in the channel to infiltrate back into the soil structure for irrigation purposes. In extreme rainfall events the products acts like a conventional channel drain, draining water to the down pipe from the roof.