Weep holes are small openings left in a brick veneer or cavity wall that allow water to drain out and air to circulate, preventing moisture build-up behind the cladding. In New Zealand's often wet climate, properly functioning weep holes are an important part of a wall's weathertightness system. Whether you're adding new weep holes or clearing blocked ones, this guide walks you through the process safely and correctly.
Why Weep Holes Matter
Brick veneer walls are not completely waterproof — some moisture always finds its way into the cavity. Weep holes at the base of the wall (typically just above the flashing or damp-proof course) allow that water to escape rather than pool and cause damage. Without them, you risk:
- Moisture soaking into the wall structure and framing
- Mould and rot in timber framing behind the brick
- Efflorescence (white salt staining) on the brick face
- Long-term structural damage
The MBIE Building Performance guidance and NZ Building Code clauses E2 (External Moisture) and E3 (Internal Moisture — though E3 primarily relates to wet areas such as bathrooms and laundries, rather than external cladding) both require that cladding systems manage water effectively. Weep holes are a key part of meeting those requirements.
Do You Need a Building Consent?
This is an important question to answer before you start. Minor maintenance — such as clearing blocked weep holes or reinstating a missing mortar joint in an existing course — is generally exempt from building consent under Schedule 1 of the Building Act 2004. However, if you are:
- Adding weep holes to a wall that never had them
- Altering the structure of the wall
- Working on a wall that is part of a weathertight remediation
…you should check with your local council before starting work. Requirements vary by region and by the scope of the job. You can find general guidance at MBIE Building Performance.
Tools and Materials You'll Need
- Angle grinder with a masonry/diamond blade, or a cold chisel and club hammer
- Safety glasses, dust mask (P2 rated), hearing protection, and gloves
- Tape measure and pencil
- Weep hole vents (small plastic inserts available from Bunnings or Mitre 10 — these keep insects out while allowing drainage)
- Stiff brush for clearing debris
Step-by-Step: Creating or Reinstating Weep Holes
1. Locate the Correct Position
Weep holes should be placed in the perpendicular (vertical) mortar joints of the first course of bricks immediately above the flashing or damp-proof course at the base of the wall. Never cut through the brick itself — always work in the mortar joint.
2. Determine Correct Spacing
As a general guide, weep holes are typically spaced at every second perpendicular joint, which works out to roughly 600–900 mm apart. Check the original construction drawings if available, or consult a bricklayer, as spacing can vary depending on wall design.
| Wall Type | Typical Weep Hole Spacing |
|---|---|
| Standard brick veneer | Every 2nd perp joint (~600 mm) |
| Cavity masonry wall | Every 2nd–3rd perp joint |
| Above lintels/openings | At least one each side |
3. Remove the Mortar
Using an angle grinder with a masonry blade (or a cold chisel and club hammer for smaller jobs), carefully rake out the mortar from the perpendicular joint to a depth of about 20–25 mm. Work slowly to avoid cracking the surrounding bricks. Keep the opening the full height of the joint — typically around 10 mm high and 10 mm wide.
Safety note: Masonry dust contains silica and is a serious health hazard. Always wear a P2 dust mask and safety glasses. Work in a well-ventilated area and wet-cut where possible to reduce airborne dust. See WorkSafe NZ for guidance on working safely with silica dust.
4. Clear the Cavity
Use a stiff brush or a length of wire to clear any mortar droppings or debris from inside the cavity. Mortar snots at the base of the cavity are a common cause of blocked drainage — remove as much as you can reach.
5. Insert Weep Hole Vents
Fit plastic weep hole vents into each opening. These allow water and air to pass through while keeping out insects (bees and wasps love to nest in open cavities). Simply press them into the cleaned joint — they should sit flush with the brick face.
6. Check for Drainage
Once complete, pour a small amount of water into the cavity from above (if accessible) or wait for rain, and confirm water is exiting through the weep holes as expected.
Clearing Blocked Weep Holes
If existing weep holes are blocked with mortar, paint, or debris, the fix is straightforward:
- Use a cold chisel or screwdriver to carefully pick out the blockage
- Flush with water to clear remaining debris
- Fit a weep hole vent to prevent future blockages
This is routine maintenance any capable homeowner can do.
When to Call a Professional
While clearing or reinstating weep holes is a manageable DIY task, you should hire a qualified bricklayer if:
- You are unsure where the flashing or damp-proof course sits
- The wall shows signs of significant water damage, cracking, or movement
- You need to add weep holes to a wall that didn't originally have them (may require consent)
- The work is part of a broader weathertightness repair
- You are working at height and need scaffolding
Poorly placed weep holes — or holes cut in the wrong location — can make weathertightness worse, not better. A licensed bricklayer will know exactly where to position them and can ensure the work meets the NZ Building Code. You can find qualified local bricklayers on tradedirectory.co.nz.
For rental properties, note that Tenancy Services Healthy Homes Standards require rental homes to be free from moisture and drainage issues — keeping weep holes clear is part of that obligation.
Licensed Building Practitioner (LBP)
