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Weep Holes: Why Your Brick Wall Is Built to Drain

Every year somebody caulks the gaps along the bottom of their brick to keep bugs out. It works on the bugs. It also traps water in a wall built on the assumption that water gets out.

Brick is not waterproof and was never meant to be

This surprises people, so it is worth saying plainly. A brick wall leaks. Fired clay absorbs water, mortar joints absorb more, and hard rain driven by wind pushes moisture through the outer face of any brick wall in the country. That is normal and it is designed in.

The design does not stop water at the brick. It catches water behind the brick and sends it back outside before it reaches anything that rots, rusts or freezes. The Brick Industry Association covers this drainage principle throughout its Technical Notes series, and every modern brick house is built on it. The weep holes along your bottom course are the exit.

What is actually behind your brick

On nearly every house built here in the last several decades the brick is a veneer. It is a single wythe standing on the foundation ledge, carrying its own weight and nothing else. The structure is the wood framing behind it.

Between the two there is an air space, commonly about an inch, and that gap is the whole point. It is not a construction gap left by accident. It is a drainage cavity. Behind it sits sheathing and a water resistive barrier, and across it run corrugated metal ties nailed to the studs, holding the brick upright against wind without closing the space.

Water that comes through the brick runs down the back face, lands on flashing and exits through the weeps. That is the entire mechanism, and it stops working if any link goes missing.

Flashing is what makes a weep hole mean anything

A weep hole with no flashing under it is decoration. Flashing is the membrane or metal that collects water in the cavity and turns it back out through the wall, and it is the part homeowners never see and builders sometimes shorten.

The detail missed most often is the end dam, a turned up corner at each end of a lintel flashing that stops water running off the side and into the wall instead of out of it. It takes a minute to form and it is invisible once the brick is laid, which is exactly why it goes missing.

• Base of the wall, at or just above the foundation ledge
• Above every window and door lintel, with weeps in the course above
• Beneath sills and copings
• At shelf angles on multi story walls
• Turned up end dams at both ends of every lintel flashing

The three kinds of weep you will find

Walk your bottom course and you will see one of three things. Open head joints are the obvious one: a vertical joint left empty of mortar, often mistaken for something the mason forgot. Rope or cotton wicks look like a short length of cord poking out of a joint, drawing water out by capillary action, and they sit closer together than open joints because they move less water. Plastic tubes are small round holes set into the joint, less common now and the easiest of the three to block.

If you cannot find any of them along the bottom course of a brick veneer wall, that is worth having somebody look at rather than assuming they are hidden. A quick check on a dry day: hold a strip of tissue at the opening. Air movement means the cavity is open behind it.

How weeps get blocked

Some blockages date from the day the wall was built. As courses go up, mortar squeezes out of the back of the joints and drops. Unless the crew keeps that cavity swept as the work rises, those droppings settle onto the flashing and bury the weeps from behind, where nobody can see them and nobody can easily reach them. It is the most common defect we find in newer veneer around Smyrna and La Vergne.

The rest happen slowly at ground level. Mulch beds topped up every spring. Sod laid over the old grade. A patio poured tight to the house above the bottom course. And then the deliberate one, where somebody decides the gaps are a defect or an insect highway and fills them with caulk, foam or mortar.

• Mortar droppings sitting on the base flashing from original construction
• Grade, mulch or new sod climbing over the bottom course
• Concrete, pavers or a poured stoop set above the weep line
• Caulk, spray foam or mortar applied on purpose
• Paint over brick, closing wicks and narrowing openings
• Dirt and insect nests packing out tubes

Why sealing them causes damage in this climate

Block the drain and the cavity becomes a tank. Water still gets in through the brick, because that never stops, and now it sits on the flashing against the back of the wall.

In Middle Tennessee that trapped water meets a repeating freeze and thaw cycle from December through February. Saturated brick that freezes spalls, meaning the face of the unit pops off, and a brick that has lost its face takes on water faster and goes downhill quickly. The same water does the same job on the joints. In a warm climate a wet cavity is a rot problem. Here it is that plus a masonry destruction problem.

The slower outcomes follow. Sill plates and sheathing stay damp and eventually rot. Ties and lintels corrode, and rusting steel expands and lifts the brick above it. Efflorescence blooms white on the face as salts get carried out of a wall holding water it should have shed.

What to do instead

If insects are the reason you want them closed, use a stainless steel or plastic weep vent sized for the opening. It keeps wasps and mice out and lets water and air through. They cost very little and go in with no tools.

If the weeps are buried, dig the grade back until the bottom course is visible and keep several inches of clear brick above soil and above any hard surface. That one job fixes more veneer problems than anything else a homeowner can do alone. Then work upstream: clean the gutters, extend the downspouts, and keep sprinkler heads off the wall.

Clearing a blocked weep gently with stiff wire is reasonable homeowner work. Drilling new ones is not. Weeps have to sit directly on flashing, and a hole drilled where there is no flashing behind it just gives water a new way in.

Related services: Masonry Waterproofing and Sealing