Soil Stack Design

Position a new stack close to a new or existing drain and near to the appliances it will be connected to. To prevent foul odors from entering the building, an external soil stack must finish at least 900mm above any opening into the house (i.e. an upstairs window) Use a 67½° offset bend to extend the stack up beyond the eaves and fit with a vent terminal or cowl to prevent birds from nesting. Internal soil stacks may terminate inside a building when fitted with an air admittance valve.

Bends at the base of stacks should be of long radius. Two 45° bends may be used as an alternative. The same principle should be used for offsets.

The distance between the centre line of the lowest branch connection and the invert of the drain should be at least 450mm.

L = 450mm up to three storeys high
L = 740mm up to five storeys high
L = one storeyheight, over five storeys

Note: If you are installing a new soil stack or drainage system, or significantly altering an existing system, you will need to inform the Building Control Department at your local Council. You will need to demonstrate that the work carried out conforms to Building Regulations: England & Wales or Scotland