Dampness within a building structure is one of the most difficult and expensive defects to put right.

The majority of damp problems are caused by condensation and water penetration through windows, doors and roof abutments. This can lead to serious issues such as dry rot and mould. That is why there are preventative measures outlined in building regulations, which must be implemented to avoid damp occurring. These preventative measures include the installation of cavity trays and weep holes.

What are weep holes in brick?
Weep holes in brick are small vertical gaps that have been left in external masonry walls. Weep holes help to maintain ventilation by enabling water to drain from the brick wall and air to circulate. Weep holes should be used in conjunction with a cavity tray.

What is a cavity tray?
Cavity trays prevent moisture from permeating to the inner leaf of a masonry wall. A cavity tray forms a gutter between the outer and inner leaves of a cavity wall, leading any water to weep vents in the external masonry walls. Cavity trays also enable air flow in the wall cavity.

Where should weep holes and cavity trays be placed?
It’s hard to know where to position cavity trays and weep holes so that they have the maximum effect. That’s why we have created a checklist which simplifies where you would expect to find these preventative measures.

Windows/Door Openings

  • Install cavity trays over ALL external door and window openings including bay windows
  • Position the cavity tray directly over the window/door head
  • When using natural stone/artificial stone heads it is best to double up the cavity trays, installing one below and one above the head
  • Ensure the cavity insulation continues to cover behind the stone head
  • Ensure the cavity trays are kept free of mortar droppings
  • Ensure weep holes are provided at each end of a horizontal cavity tray at a maximum of 900mm centres


Roof Abutments

  • Install cavity trays at roof abutments, both horizontal and pitched
  • For pitched roof abutments, it is best to use purpose made stepped cavity trays
  • Ensure the cavity trays are kept free of mortar droppings
  • Ensure a weep hole is provided at the base of stepped cavity trays


Rendered Walls

  • For rendered masonry walls and timber frame walls, cavity trays should be installed with stop-ends over openings and lower level abutments
  • In rendered masonry walls weep holes can be omitted as long as there is no fair-faced brickwork above the rendered panels. Weep holes should not be used to compensate for poor render
  • In rendered timber frame walls, weeps holes with open perp joints need to be included. The open joints need to be the total depth of the ‘perps’ and installed at a minimum of 900mm centres or at least 2 per opening
  • Ensure ALL weep holes are kept clear of render to make sure they work efficiently


Don’t forget...
Weep holes must be maintained and protected so that they stop mice and wasps from entering cavity walls. When exposed to elements, weep holes can slowly expand over time, making it a perfect walkway for pests.

Getting rid of mice is no easy task, which is why it is sensible to invest in weep hole covers. Made from stainless steel or plastic, weep hole covers are quick and easy to fit. They slot into weep hole gaps so that pests cannot enter.

Download our cavity trays and weep holes checklist to ensure you comply with the requirements for building regulations and our Technical Manual.

By Anna Symington

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