A cavity brick or masonry wall is not designed on the assumption that its outer leaf will keep every drop of rain out. Wind driven rain can pass through mortar joints, hairline cracks and the porous face of masonry. The cavity exists specifically to separate that wet outer layer from the structure and internal finishes, giving water a controlled place to fall, collect and drain.
Weep holes and cavity flashing are the two details that make that moisture-management system work. Flashing catches water inside the cavity and directs it towards the exterior. Weep holes are the small, deliberate openings that let the water escape. Remove either part and the cavity can become a reservoir rather than a drainage space.
BUILTLY is building a record of completed Australian homes that credits the builder, designers and trades behind each one.
This guide explains what homeowners can see, what becomes concealed, how the elements should work together and which records are worth keeping. For the full sequence around wall construction and inspection, refer to the BUILTLY complete guide to building a house in Australia.
What Weep Holes Do
Weep holes are drainage outlets formed in the external masonry leaf. In ordinary brickwork they often look like a vertical mortar joint that was intentionally left open. They are usually placed in the course immediately above cavity flashing at the base of a wall, above a window or door lintel, over a shelf angle, and anywhere else flashing interrupts the downward path of water.
Their primary function is gravity drainage. Rain that reaches the cavity runs down the back face of the outer leaf. The flashing turns that water outward, and the weep holes provide the final path through the face brickwork. They can also assist local air movement within the cavity, helping damp masonry dry after a weather event, although they are not a substitute for a deliberately designed ventilation system where one is required.
The gaps are small because they only need to release water while maintaining the brick bond and appearance. They may be open perpends, formed openings or fitted with proprietary vents. A homeowner may mistake them for poor workmanship and ask for them to be filled. Landscapers, renderers and paving contractors also cover them without appreciating their purpose. That well-intentioned work disables the drainage system.
Why clear outlets matter
Water trapped above flashing searches for another route. It can bridge across mortar droppings, track through ties, move around flashing ends or rise until it reaches an internal surface. A blocked hole does not always produce a stain directly behind that location. Moisture may travel sideways before showing up, which makes diagnosis difficult and can lead to repairs in the wrong place.
Clear does not mean unprotected. Purpose-made guards can reduce insect entry while preserving the opening. The guard must not act like a plug, wick or collection point. In bushfire-prone areas, any opening treatment must also suit the bushfire construction requirements that apply to the site.
What Cavity Flashing Does
Cavity flashing is a water-resistant sheet or formed component built into the wall to intercept moisture and direct it outward. It creates a sloping or positively drained tray beneath the area of cavity where water will collect. The inner edge is turned up or connected to the backing construction, while the outer edge reaches the masonry face or the weep-hole line.
Flashing is required where the natural downward drainage path changes. The exact arrangement depends on the wall type, exposure, opening geometry and design documentation, but the recurring locations are predictable.
At the base of the cavity
Base flashing or the damp-proof course prevents cavity water from reaching the slab edge, subfloor or framing and turns it through the lowest row of weep holes. It must sit above the relevant external ground and paving clearances so surface water cannot bypass it.
Above windows and doors
Water running down the cavity meets the head of an opening. A head flashing or cavity tray carries it over the lintel and out through weep holes above. End dams or turned-up ends stop water running off the tray into the jamb cavity.
Around penetrations and changes in level
Pipes, meter boxes, balconies, roofs abutting walls and stepped foundations interrupt the cavity. Each needs a detail that sheds water around or over the interruption without creating an inward fall, unsealed corner or dead end.
Material compatibility
Flashing material must remain durable in contact with mortar, masonry, treated timber, metals and the surrounding exposure. Flexible polymeric and metal flashings behave differently at corners and laps. Metallic materials can corrode when incompatible metals touch or when mortar chemistry and coastal exposure are not considered. A product being easy to fold does not make it suitable for every wall.
Flashing also needs continuity. Individual lengths must overlap by the specified amount, joints must be sealed where required, corners must be formed without pinholes, and the outer edge must discharge rather than turn back into the cavity. A nominal strip of flashing in the correct location is not enough if its laps and terminations cannot manage real water.
How Weep Holes and Flashing Work Together
Think of the wall as a sequence of drainage planes rather than one waterproof face. The outer masonry sheds most rain. The clear cavity separates that wet layer from the frame or inner masonry leaf. Flashing catches the water at the base and at interruptions. Weep holes discharge it outside. Each layer assumes a small amount of water may pass the layer before it, then controls where that water goes next.
On a brick veneer home, the building wrap and sarking system forms the complementary weather barrier on the other side of the cavity. If rain crosses the brick outer leaf, it should fall through a cavity kept clear of mortar bridges, stay outside the wrap, land on correctly integrated flashing and leave through a weep hole. Window head and sill flashings connect these planes around the most vulnerable openings.
This explains why isolated inspection is unreliable. Perfect weep holes cannot drain water if the flashing stops short. Correct flashing cannot perform if mortar droppings bridge the cavity or block the outlet. Good wrap cannot save a window opening where its laps direct water behind the head flashing. The wall works as an assembly, so photographs and checks should capture transitions between materials, not only broad elevations.
Moisture at wet areas, roofs and balconies follows different primary waterproofing rules, but the same principle applies: water needs a continuous path away from vulnerable materials. The BUILTLY guide to waterproofing in Australia explains those systems and where responsibility usually sits.
Australian Standards
AS 3700, Masonry structures, is the principal Australian Standard for the design and construction of masonry. It addresses durability, wall ties, cavities, damp-proof courses, flashings and drainage details as part of a complete masonry system. Housing projects may also use the relevant housing provisions and accepted construction manuals where permitted, but project drawings and specifications still need to resolve the actual wall junctions.
AS/NZS 2904, Damp-proof courses and flashings, sets material requirements and test methods for products used to resist moisture in masonry. It deals with properties such as water resistance, durability and compatibility. Product markings and technical data should identify the applicable classification and limitations. The reference should be read with the current National Construction Code and the project documentation rather than treated as a stand-alone installation drawing.
For the barrier against rising and lateral ground moisture, including its material choices and relationship to finished levels, see the companion guide to damp-proof course in Australia.
Standards establish minimum technical outcomes. They do not remove the need for a buildable detail. An architect, building designer or engineer may specify wider trays, proprietary systems or more conservative materials because of severe weather exposure, a coastal location, unusual geometry or the consequences of leakage. Manufacturer instructions can also add mandatory lap, sealing and support requirements.
Homeowners do not need to interpret every clause. Ask which drawing shows the base flashing, window head flashing, end dams and weep-hole spacing, then ask the builder to confirm the installed work follows it. Confirming the person responsible for that work is properly authorised also matters. BUILTLY explains the process in how to check a builder's licence in Australia.
Common Defects
Most failures are installation and coordination problems rather than exotic product failures. Bricklayers, window installers, cladding trades, renderers, plumbers and landscapers can all affect the final drainage path.
Blocked or rendered-over weep holes
Mortar smears, render, paint, sealant, pest treatments, garden soil and paving can close the outlet. This is common, visible and often preventable. A row of partly covered holes should be raised before handover, and later landscaping must preserve the required clearance.
Mortar droppings in the cavity
Excess mortar can collect on flashing and form a dam or bridge from the outer leaf to the frame. Water then bypasses the intended route. Cavity battens, boards and progressive cleaning help, but evidence should be captured before the wall becomes inaccessible.
Missing, flat or back-falling flashing
Flashing omitted above an opening leaves water sitting on the lintel or moving into the jamb. Flashing laid flat, sagging or falling inward can hold water instead of draining it. The fall and outer termination should be apparent while the cavity remains open.
Incorrect laps and missing end dams
Short overlaps, unsealed joints and punctured corners let water escape behind the tray. Above an opening, missing end dams allow collected water to pour into the cavity at each side, commonly producing staining around window reveals.
Incompatible or corroding material
An unsuitable metal can corrode in alkaline mortar, coastal air or contact with another metal. Thin material can tear during bricklaying. Once perforated, flashing may look present at its exposed edge while no longer forming a continuous barrier.
External levels built too high
Driveways, paths and garden beds added above the designed level can cover weep holes and bridge the damp-proof course. The wall may have been compliant at handover and become vulnerable later, so owners should retain the approved level information before changing landscaping.
Persistent moisture can damage framing and masonry components and may contribute to conditions that become structural defects in a new build. Early investigation is usually less disruptive than waiting for visible internal damage to spread.
What to Check During and After Construction
Weep holes are unusually homeowner-friendly inspection points because they remain visible. Flashing is different: most of its critical laps and corners disappear as brickwork rises. Time checks to the relevant stages described in the construction stage explained in Australia.
Before and during brickwork
- Locate the approved wall sections and opening details before work begins
- Record the flashing product name, batch information and technical data sheet
- Photograph base flashing continuously around each elevation before it is concealed
- Photograph head flashings, end dams, corners, steps and service penetrations close up
- Check flashing falls towards the outer leaf and reaches the intended outlet line
- Look for tears, unsealed laps, pinched corners and mortar collecting on the tray
- Confirm the cavity remains clear and the wrap is not displaced or punctured
At lockup and handover
- Walk every elevation and identify a consistent line of open weep holes
- Check for outlets above windows, doors and other flashed interruptions
- Use a torch to look for obvious mortar blockage without inserting tools or damaging guards
- Confirm render, paint and sealant stop clear of the openings
- Check paving, soil and mulch remain below the required clearance line
- Look for damp staining, efflorescence, rust marks or swollen internal finishes after rain
- Record concerns in writing with dated, location-specific photographs
After moving in
Keep outlets clear during routine maintenance and after landscaping. Do not probe flashing with screwdrivers, pressure-wash directly into holes or fill an opening because insects have appeared. Use a compatible guard and investigate repeated water discharge, staining or internal dampness rather than masking the symptom.
After severe wind driven rain, photograph any wet areas before they dry and note the direction of the weather. A clear record helps a builder or consultant connect an internal symptom with an external junction. If opening-up work is proposed, agree on its scope and how the area will be reinstated before work begins.
BUILTLY Verification for Concealed Moisture Details
A finished brick wall shows the weep holes but not the flashing behind them. The details that prove the system is continuous are visible for days during construction and then concealed for decades. That makes them exactly the kind of work worth recording before the next trade closes the cavity.
A useful record includes wide photographs locating each elevation, close photographs of laps and end dams, the flashing product data, dates, and the contributors responsible for masonry and window installation. The sequence matters because one isolated photograph cannot show continuity around the building.
BUILTLY is building a record of completed Australian homes that credits the builder, designers and trades behind each one.
Frequently Asked Questions
What are weep holes in a brick wall?
Weep holes are deliberately open vertical joints near the base of a masonry cavity and above openings or other interruptions. They let water collected by cavity flashing drain to the exterior and help the cavity ventilate. They are part of the wall design, not unfinished mortar joints, and should not be filled simply because they look like gaps.
How far apart should weep holes be in Australia?
The required spacing depends on the wall detail, the applicable construction provisions and the design documents. A common residential arrangement places them at regular centres along flashing, with additional openings positioned near corners and ends. Homeowners should compare the installed pattern with the approved drawings and masonry specification rather than relying on one universal measurement.
Can insects enter through weep holes?
Open weep holes can admit insects, but the answer is a purpose-made weep-hole guard that preserves drainage and airflow. Silicone, expanding foam, mortar, steel wool and improvised mesh can obstruct the opening or corrode. Any guard should be compatible with the masonry system, bushfire requirements and the opening dimensions.
Can landscaping or paving cover weep holes?
No. Finished ground, garden beds, mulch, paving and render should remain below the weep holes and damp-proof course by the clearance required for the project. Covering the outlets can bridge the moisture barrier, direct surface water into the cavity and make termite inspection more difficult. Changes to external levels after handover are a common cause of otherwise avoidable moisture problems.
How can missing cavity flashing be confirmed after construction?
Some flashing edges can be seen through weep holes or at exposed ends, but much of the installation becomes concealed. A building consultant may use moisture readings, a borescope or selective investigation where symptoms justify it. Those methods do not always prove every lap and termination. Dated photographs taken before the brickwork closes the cavity remain the most useful evidence.