What are the weep holes in cavity walls?

Author: Devonte Moen  |  Last update: Thursday, December 18, 2025

Weep holes in brick walls usually appear as small vertical spaces that are left during construction in the mortar of brickwork. They allow moisture to escape from brick cavity walls, which helps to prevent the buildup of water and condensation.

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.

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.

What Is A Weep Hole And What Do They Do?

Can water enter house through weep holes?

Weep holes are often located at the bottom of brick exterior walls. They look like vertical gaps in the mortar joints between bricks. Because brick masonry is porous, water may penetrate the surface and get behind the wall.

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 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.

Can water leak 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.

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.

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.

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.

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.

Why is water coming through my walls after rain?

Penetrating damp may take place where there is a defect in the roof, render, brickwork, clogged or damaged gutters or downpipes and window frames that allow for water to enter the building materials.

What does a weep hole look like?

Weep holes are usually located at the base of brick exterior walls. They appear to be vertical gaps in the mortar joints between the bricks. Water may seep through the surface and enter the wall's interior because brick masonry is porous.

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.

What happens if water gets in weep holes?

You will always spot the weep holes in brick walls because bricks and mortar are porous. It means water can pass through them. This water will run towards the backside of the brick wall, and if there is no drainage, water will settle inside, slowly decaying the walls.

Is it OK to cover weep holes?

While they can provide an entry point for pests, covering weep holes in brick walls is a definite no-no due to the damage this can cause to a building's structure. Instead, high quality screens and covers can be used to keep vermin out whilst maintaining the utility of these very important openings.

What happens if you seal weep holes?

If the weep holes are blocked to prevent drainage from occurring, the water can build up in the extrusion and ultimately leak into the wall cavity if a leakage path is available.

Can snakes get into a house through weep holes?

small or young snakes can come into a house through the weep holes in the masonry, though assorted insects and small rodents can also get in that way and they (and warmth, if sunlight strikes the wall there) would be a primary reason a snake would enter.

What are the disadvantages of a weep hole?

Weep holes serve an important role in your home's drainage and ventilation, but they can also provide pests such as mice and cockroaches an easy access point into your home.

Will silicone caulk keep mice out?

Because your home's foundation is close to the ground, it provides easy access for curious mice to enter. Take a walk around your home and look for small cracks and gaps in the foundation. Seal the gaps with silicone caulk, which is tough enough to withstand exterior elements and will keep mice out.

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