Weep Holes in Brick Homes: What They Are and Why You Must Never Block Them

If you own a brick home in Kitchener-Waterloo — particularly one built after the 1970s — you have weep holes. Those small gaps in the mortar at the base of brick courses are not a defect or a mistake. They are a critical, intentional drainage feature, and blocking them is one of the most damaging things a homeowner can accidentally do to their home. Here's everything you need to know about weep holes, why they exist, and how to maintain them.

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What Are Weep Holes and Where Are They Located?

Weep holes are small openings left at the base of the exterior brick courses during construction. They are typically formed by leaving a mortar joint empty rather than filling it, creating a gap approximately 10mm high and 65mm wide (a full unfilled head joint). In some construction methods, they are created by inserting small rope wicks or open tubes through the mortar to create a drainage channel.

You'll find them at specific locations in the brick veneer:

• At the base of the first course of brick above the foundation wall, foundation waterproofing, or any flashing — this is the primary drainage point for the wall cavity
• Above window and door lintels — wherever a flashing is installed beneath the brick, weep holes must appear above it to drain any water that infiltrates the brick and collects on the flashing
• Above any horizontal shelf angle or ledger that supports brick at upper floor levels

In properly constructed brick veneer buildings — which includes the vast majority of brick homes built in the Kitchener-Waterloo region from the 1970s onward — weep holes appear approximately every two to three bricks horizontally (every 600-900mm) at each drainage level. If your brick home appears to have no weep holes, either they are blocked or the construction predates modern brick veneer standards and uses a different wall assembly.

Related moisture-defence guides: grading soil around your foundation · underground downspout drainage · eavestrough sizing.

How Moisture Gets Into and Out of Brick Veneer Walls

To understand why weep holes are essential, you need to understand how modern brick veneer construction is designed to manage moisture. Brick is not waterproof — it absorbs and transmits water. During a heavy rainstorm, water infiltrates through brick and mortar joints and enters the cavity between the brick veneer and the structural wall behind it.

This is entirely by design. Brick veneer construction does not attempt to keep all water out of the brick. Instead, it manages water through a system of three components:

1. The cavity: A 25-50mm air space between the back of the brick veneer and the sheathing or insulation on the structural wall. This cavity allows water that penetrates the brick to drain down to the flashing rather than reaching the structural wall.
2. The flashing: A waterproof membrane (sheet metal, rubberized asphalt, or self-adhering membrane) installed horizontally at the base of the cavity wall. Flashing is sloped toward the exterior to direct any water in the cavity out through the weep holes.
3. Weep holes: The exit point for water that has collected on the flashing. Without weep holes, the flashing has nowhere to drain — water backs up in the cavity and eventually saturates the insulation, wets the sheathing, and enters the wall assembly.

This drainage system works brilliantly when all three components are intact. Remove any one of them — including the weep holes — and the system fails. Water that enters the brick has no exit and accumulates in the cavity.

Why Weep Holes Get Blocked: The Common Culprits

Despite being intentional and critical building features, weep holes are regularly blocked by well-meaning homeowners and contractors who don't understand their purpose. The most common ways weep holes get blocked in Ontario homes:

Caulking by homeowners: The most common cause. Homeowners doing exterior caulking see what appears to be gaps in the mortar — open joints — and assume they're defects that need to be filled. Without understanding that these gaps are intentional drainage points, they caulk them shut. A caulked weep hole is a completely blocked weep hole.

Painting over: Some exterior paints bridge small gaps. Multiple coats of exterior paint applied over decades can gradually reduce or eliminate the weep hole opening, particularly in older brick homes that have been painted.

Mulch and soil accumulation: Garden beds against the foundation — a common Ontario landscaping feature — accumulate mulch and soil that gradually buries the lower courses of brick. Weep holes at the base of the wall become buried under garden bed material, completely blocking their function.

Insect nests: Mud dauber wasps and other cavity-nesting insects commonly block weep holes with mud nests. A weep hole is exactly the size and shape these insects prefer for nest sites. Nests appear as plugs of mud visible in the opening.

Mortar droppings during construction or repair: Mortar from repointing work can drip down into the cavity and accumulate on the flashing, potentially blocking the weep hole openings from the inside. This is less common but can occur after mortar joint repair work.

Debris accumulation: Leaves, dirt, and organic material can partially or completely block weep holes, particularly in sheltered areas where debris accumulates in corners.

Consequences of Blocked Weep Holes: Why This Matters So Much

Blocked weep holes cause damage that is slow-developing, hidden inside the wall, and potentially very expensive to repair. Because the damage develops over months and years before becoming visible, homeowners often don't connect the eventual symptoms to the root cause.

What happens when weep holes are blocked:

• Cavity moisture accumulation: Water that infiltrates through the brick during rain has nowhere to go. It accumulates on the flashing and, when the level rises, saturates the cavity insulation, wets the sheathing, and eventually contacts the framing.
• Sheathing and framing rot: Once moisture reaches the wood structural elements behind the brick veneer, biological degradation begins. Mold grows rapidly on wet wood, and rot follows if moisture is persistent. Framing damage behind brick veneer requires brick removal to access — repair costs in Ontario typically run $3,000-$15,000 depending on extent.
• Insulation degradation: Wet insulation loses its thermal performance and can become a mold habitat. Batt insulation in a persistently wet wall cavity is effectively useless as a thermal barrier and acts as a moisture reservoir.
• Efflorescence on brick face: As water trapped in the wall moves outward through the brick, it carries dissolved salts to the surface and deposits them as white efflorescence staining. Persistent efflorescence on brick — particularly appearing repeatedly after cleaning — is often a sign of chronic moisture problems behind the wall including blocked weep holes.
• Freeze-thaw damage to brick: Water trapped in the cavity freezes in Ontario winters, expanding against the back of the brick veneer. Over years, this can cause brick faces to spall and mortar joints to deteriorate from the inside.

The freeze-thaw factor deserves emphasis for local homeowners: Kitchener-Waterloo walls cycle through dozens of freezes and thaws between November and April — among the most punishing masonry climates in southern Ontario. A blocked weep hole that might cause slow, tolerable damage in a milder region accelerates spalling and interior rot dramatically here, because every trapped litre of water gets dozens of expansion cycles per winter to do its work.

"Every spring we see brick homes with white staining and efflorescence on the lower brick courses. One of the first things we check is whether the weep holes are open. In many cases they've been caulked, painted over, or buried under mulch — and moisture has been trapped behind the brick for years."

— Devon, D&D Home Services Founder

Proper Weep Hole Maintenance: Keeping Them Clear

Maintaining weep holes requires only periodic inspection and clearing — a simple task that takes 15-20 minutes for most homes but protects against potentially thousands of dollars in hidden moisture damage.

Annual inspection: Once per year — ideally in fall as part of your exterior walkthrough — examine all weep holes around the base of your brick veneer and above each window and door. Look for:

• Mud dauber wasp nests (visible as grey clay plugs in the opening)
• Debris accumulation (leaves, dirt, mulch)
• Caulk or paint bridging the opening
• Mulch or soil level approaching or above the weep holes

How to clear blocked weep holes:

• Insect nests: Remove with a toothpick, thin screwdriver, or bent wire. Be sure the cavity behind is also clear — sometimes nests extend into the cavity opening.
• Debris: Clear with a toothpick or thin wire. Flush with a thin stream of water to verify the hole is open and draining.
• Caulk blocking: Carefully remove caulk from weep holes using a sharp utility knife or awl. Do not apply caulk to these joints in future maintenance sessions.
• Mulch burial: Keep all mulch and garden bed material at least 6 inches below the weep hole level. If garden beds have raised to the point of burying weep holes, the bed needs to be lowered.

Weep hole covers: If insects are repeatedly nesting in your weep holes, weep hole covers (also called weep hole ventilators or insect screens) are available from masonry suppliers. These small plastic inserts allow water and air to pass through while physically blocking insects from entering. They are an excellent solution for homes with persistent wasp or bee nest problems in weep holes.

Weep Holes in New Construction: Ontario Building Code Requirements

The Ontario Building Code (OBC) requires weep holes in all exterior masonry veneer construction. Current standards specify weep holes at maximum 600mm spacing horizontally at all flashing levels. This requirement ensures that all new brick veneer construction in Ontario has proper drainage built in from the start.

If you're buying a new home or have had brick construction done recently, the weep holes should be present and properly placed by default — they're an inspection item. If you cannot find weep holes on what appears to be a modern brick veneer wall, it's worth asking the builder or contractor about the drainage design.

Older homes — particularly those built before the 1970s — may use a different wall construction entirely (solid masonry or full-cavity construction) that may not have the same weep hole system. If you're unsure about your home's wall construction, a qualified home inspector or masonry contractor can advise you on the specific system used and any maintenance implications.

Regular exterior maintenance — including keeping weep holes clear, managing mulch levels, and proper gutter function to limit water volume reaching the wall — protects your brick home's wall assembly for decades. Our soft washing service cleans brick exteriors without the high pressure that can damage mortar joints or drive moisture into the wall.

Frequently Asked Questions

What are the small holes at the bottom of my brick house?

Those are weep holes — intentional open joints, roughly 10 mm wide, left every 600–900 mm at the base of brick veneer and above windows and doors. They drain rain water that naturally penetrates the brick out of the wall cavity. They are a feature, not a defect.

Can you fill or caulk weep holes in brick?

No — never. Caulked weep holes trap water in the wall cavity, where it saturates insulation, rots sheathing and framing, and freezes against the back of the brick each winter. If yours have been caulked, carefully cut the caulk out with a utility knife or awl.

What happens if weep holes are blocked?

Moisture accumulates invisibly in the cavity: wet insulation, mould, sheathing and framing rot, recurring efflorescence (white staining) on the brick face, and freeze-thaw spalling. Because repairs require removing brick to access the damage, Ontario repair bills typically run $3,000–$15,000.

How do you keep bugs and mice out of weep holes?

Use ventilated weep hole covers (insect screens) from masonry suppliers — small inserts that pass water and air while physically blocking wasps, bees, and rodents. Never plug the holes with caulk, steel wool jammed tight, or mortar; the hole must keep draining.

How many weep holes should a brick house have?

One every 600–900 mm (about every 2–3 bricks) along every flashing level — the base course above the foundation, above each window and door lintel, and above any shelf angle. The Ontario Building Code requires maximum 600 mm spacing in new masonry veneer construction.

Do older brick homes have weep holes?

Kitchener-Waterloo homes built from the 1970s onward almost always do. Pre-1970s homes may be solid masonry or older cavity designs without modern weeps — a different wall system with its own maintenance rules. If you can't find weep holes on an older home, have a masonry contractor or home inspector identify the construction type before making changes.

How do I unblock a weep hole?

Wasp nests and debris clear with a toothpick, thin screwdriver, or bent wire; verify drainage with a thin stream of water. Cut away any caulk or paint bridging the opening, and pull mulch or soil back so beds sit at least 6 inches below the weep line.

Devon Moore, Operations LeadCo-Founder & Operations Lead — D&D Home Services

Devon Moore is the co-founder and Operations Lead at D&D Home Services, with hands-on experience cleaning hundreds of homes across Kitchener-Waterloo, Cambridge, and Guelph.