Weep Vents

Weep vents are small gaps or fittings left in the vertical mortar joints of the outer leaf of brickwork, spaced along the base of a cavity or above a lintel, that let water collect from within the cavity drain back out to the outside.

Any cavity wall lets some water into the cavity over time, driven rain that gets through the outer brickwork, or condensation within the cavity. That water is meant to run down the inner face of the outer leaf and out through the weep vents, rather than build up or find its way inward. Without them, water collecting on a cavity tray or at the base of the cavity would have nowhere to go.

Where there is not sufficient water to drain, the weep vents also provide some ventilation into the cavity of the wall.

Along the base of a cavity wall, and above any cavity tray built into a lintel over an opening. Anywhere a cavity tray directs water to the outer leaf and it needs a route out.

Spacing and type (open perpends, or a proprietary plastic weep vent fitting) follow manufacturer guidance for the cavity tray or DPC system they're draining, and need coordinating with the brickwork coursing so they land where the tray is actually collecting water.

Weep vents that get blocked (by mortar droppings during construction, or later by insects or debris) stop doing their job invisibly, since the water backing up behind them isn't visible from outside. Keeping the cavity clear of mortar snots during construction matters more than the weep vents themselves for this reason.

• Facing brick: the weep vents sit within the outer leaf's mortar joints
• Lintel: drains via the weep vents wherever its cavity tray collects water
• DPC: where a cavity tray is used, the water will track across the cavity onto the DPC on the outer wall. The weep vents are positioned directly on the course where the DPC is laid.