What is the purpose of weep holes in a cavity wall?

Author: Malachi Quigley  |  Last update: Tuesday, April 14, 2026

Weep hole vents help to prevent the build-up of water in the wall, which can lead to rot and eventually damage to the structure of the building.

Do you need weep holes in cavity walls?

Weep holes are a crucial component in the maintenance and longevity of new build homes. They play a vital role in managing moisture levels within wall cavities, preventing the buildup of dampness and mould which can compromise both the structural integrity and the healthiness of the living environment.

Are weep holes really necessary?

Without masonry weep holes, or if the existing drainage system is blocked or broken, capillary action can result in the water becoming trapped inside the cavity wall.

What happens if you block weep holes?

Blocking your window weep holes predisposes the window structure to water damage, rust, and corrosion ultimately reducing your window's lifespan.

Do weep holes let cold air in?

While the first thought may be, “Won't those little holes let cold air in (or warm air out), the reality is these are the window's weep holes. They are designed and placed to drain water out of the window frame, while preventing airflow into your new pole building.

WEEP VENTS & CAVITY TRAYS EXPLAINED!! Ft Minecraft

What is the alternative to a weep hole?

As an alternative to weep holes, most new construction will connect the drainage zone to a perforated drainage pipe located behind the base of the wall outfalling to a manhole.

When did weep holes become code?

Even if you used the code as a basis of the requirement for weep holes, you would be surprised to learn that weep holes were nor mandated in the single family code until 1983 CABO, mandated by the 1985 Kentucky Building Code. Home inspectors are calling out missing weep holed on house built before 1985.

What is the problem with weep holes?

Problems With Weepholes

If weep holes are left unprotected in brick walls they provide access to the wall cavity for rodents and insects. Swarming bees and European Wasps love creating nests in cavities.

Are weep holes required by code?

Weepholes shall be provided in the outside wythe of masonry walls at a maximum spacing of 33 inches (838 mm) on center. Weepholes shall be not less than 3/16 inch (5 mm) in diameter. Weepholes shall be located immediately above the flashing.

Can mice get in through weep holes?

It's obvious that small pests such as cockroaches and spiders can crawl through weep holes, but vertebrate pests such as lizards, snakes and even mice can also squeeze through a normal weep hole.

Can water seep through weep holes?

This research demonstrated that even under truly extraordinary conditions water rarely enters the weephole and even if it does it cannot be blown high enough up in the cavity to create internal damp problems. To understand why, it's important to look at the details of a correctly constructed cavity wall.

Can bugs get in through weep holes?

Your weep holes are an important part of your home's drainage and ventilation system, but they're also vulnerable to pest infestation. Cockroaches, rodents, and spiders can easily enter your home through these gaps in your brick cavity walls.

Can I drill my own weep holes?

It is difficult to add weep holes after the walls are constructed. If the weep holes are drilled, they will typically puncture the flashing. This is true even if a special guide is placed on the drill. If the hole does not go all the way through the mortar then it will be ineffective.

Are weep holes mandatory?

Yes, Australian building codes mandate weep holes in masonry to ensure proper drainage and ventilation, safeguarding structural integrity and preventing moisture-related issues in buildings.

Should there be an air gap in cavity wall?

The air gap between the inner and outer layers, combined with insulation material, helps reduce heat transfer, keeping the interior of the building warm in winter and cool in summer. Moisture Control: Cavity walls also act as a barrier against moisture infiltration.

How do you know if a cavity wall is filled?

If you're wondering how to tell if you have cavity wall insulation, there are a few telltale signs you can look for. The simplest way is to check your brickwork for drill holes. If you notice small, evenly spaced holes that have been filled in, this is a sign that cavity wall insulation is installed.

How far apart are weep holes in cavity walls?

Weep holes should be spaced every 450mm along the run of cavity trays over lintels and 900mm over horizontal cavity trays.

Why doesn't my house have weep holes?

Why are there no weep holes? The reasons vary, but the house's builder forgot to include them, or the homeowners didn't want them. Sometimes homeowners don't want weep holes because they retract from the house's appeal – think smoothly rendered brick houses.

Are weep holes necessary?

Weepholes are an important component of a building or structure's drainage system. Moisture can enter a building in several ways, including through direct penetration, such as heavy rain or flooding, as well as water rising via capillary action.

What is the primary purpose of a weep hole?

So what exactly is a weep hole? A weep hole is a passage for water to escape a building envelope. Weep holes serve an important purpose of a home; they allow the home to “breathe” as some say. Since there are many chances for water to enter the home, weep holes allow for water exit.

Can a house flood through weep holes?

Do I Need To Plug Weep Holes During a Flood? No. Unless your home is a submarine the exterior materials along with doors and windows are not watertight and will succumb to the flood waters.

Where should weep holes be placed?

Weep holes are typically found in the outer masonry leaf of cavity walls, just above the flashing. They can also be found above windows, doors or other penetrations. They should be provided at regular intervals so as to allow any moisture collected by cavity trays to escape.

What are the requirements for a weep hole?

Weep holes shall be provided in the exterior wythe of masonry walls and shall be at a maximum spacing of 33 inches (838 mm) on center (o.c.). Weep holes shall not be less than 3/16 inch (4.8 mm) in diameter.

Where must weep holes be provided?

Gravity draws water to the bottom of the wall, just above the foundation, where weep holes allow it to escape. They are located above all windows, doors, and other openings. Weep holes are also located on window tracks.

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