Weep Hole
/ wiːp həʊl /
Also known as: weephole, drainage outlet, cavity drainage hole
Definition
A weep hole is a small opening left in the perpend (vertical) mortar joints of the outer leaf of a cavity wall, positioned immediately above a cavity tray, lintel flashing, or the base of the cavity. Its purpose is to allow water that collects on the tray to drain out through the face of the wall rather than accumulating and overflowing into the inner leaf.
In practice
Weep holes are formed at every other perpend joint - approximately every 450mm - in the brick course immediately above each cavity tray. They can be formed by simply leaving the perpend mortar joint open, by inserting a proprietary plastic weep hole insert (which allows water out while preventing insect entry), or by using a purpose-made open perpend brick unit.
Weep holes are also critical in retaining walls, where they relieve the hydrostatic pressure of groundwater behind the wall. A blocked weep hole on a retaining wall allows water pressure to build, greatly increasing the lateral load and risking structural failure. On older properties, weep holes above lintels are often rendered or pointed over during maintenance, causing concealed water buildup and internal damp.
Building Regulations
Approved Document C requires that cavity walls are constructed so that water cannot pass from the outer leaf to the inner leaf. Cavity trays with weep holes at all changes of level - above lintels, at DPC level, and where the roof abuts the wall - are essential to achieving this. Omitting weep holes above cavity trays is a common construction defect that leads to concealed water ingress.
Full Building Regulations guidance