How to keep water out

Blog Post
Diagram of a cavity tray

Condensation and water penetration through windows, doors, and roof abutments are the leading causes of moisture problems. It can be difficult and expensive to deal with damp, so preventative measures using cavity trays and weep holes are best.

Here’s where to position your cavity trays and when to add weep holes.

Windows and 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.
  • Double up the cavity trays if using natural stone/artificial stone heads - installing one below and one above the head.
  • Ensure the cavity insulation continues to cover behind the stone head.
  • Install weep holes 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’s best to use purpose-made stepped cavity trays.
  • Provide a weep hole at the base of stepped cavity trays.

Rendered and timber frame walls

  • Install cavity trays with stop-ends over openings and lower level abutments.
  • In rendered timber frame walls, use weeps holes with open perp joints. The open joints should be the total depth of the ‘perps’ and installed at a minimum of 900mm centres or at least two per opening.

Ensure ALL weep holes are kept clear of render and keep ALL cavity trays free of mortar droppings to ensure they work efficiently. For more details, please view the LABC Warranty Technical Manual.


Please Note: Every care was taken to ensure the information was correct at the time of publication. Any written guidance provided does not replace the user’s professional judgement. It is the responsibility of the dutyholder or person carrying out the work to ensure compliance with relevant building regulations or applicable technical standards.


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