Dampness in a building structure can be one of the most difficult and expensive defects to put right.

With the majority of moisture problems arising from condensation and water penetration through windows, doors and roof abutments, preventative measures need to be put into place. But it can be confusing to know when cavity trays and weep holes are required to keep the water out!

We have tried to simplify where to position your cavity trays and when to add weep holes below.

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.

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