Brick Weep Holes and Flashing: What the Holes Are For, the Through-Wall Flashing Behind Them, the 1 in. Air Space, Why You Never Fill Them, and What Fixing a Wall Without Them Costs

How a brick wall stays dry

Brick veneer is a rain screen, which is a way of saying it is the first plane of protection and it is expected to get wet through. Behind the brick is a 1 in. air space, then the sheathing membrane or the ICF foam, which is the second plane and the one that has to stay dry. Water that gets through the brick runs down the back of it in the air space. At the bottom of the wall, and over every window and door, and on top of every shelf angle, a through-wall flashing catches it: a sheet of membrane or metal that starts up the wall behind the membrane, comes down across the air space, and turns out over the front edge of the brick. The water runs along the flashing and out the weep holes, which sit in the course directly above it.

Three parts, and all three have to be there. Weeps with no flashing drain nothing, because the water runs past the hole to the bottom of the cavity. Flashing with no weeps is a bathtub. An air space full of mortar droppings bridges the water from the brick to the sheathing. The code sets the weeps at not more than 800 mm apart, about every third brick, and the air space at 25 mm. Masons who have been doing this for thirty years do it in their sleep, and a wall built without it was built by somebody else.

What the weeps look like, and what people do to them

An open head joint, which is the vertical mortar joint left empty between two bricks, or a plastic vent insert, a little grille that keeps the bugs out and lets the water through. Along the bottom course above the foundation, in the course above every lintel, and above any shelf angle partway up a wall.

1. Caulking them. The commonest. A tube of silicone on a Saturday, done for bugs and drafts. The water in the cavity now has no exit, and it finds one through the sill plate.
2. Spray foam. Worse, because it goes into the cavity and bridges it, and it is a day with a grinder to get back out.
3. Mortar. A handyman pointing the wall “fills the gaps”. Same problem, and now the wall looks like it never had them.
4. Burying them. A new patio, a raised garden bed, a deck ledger or a stone skirt set over the bottom course puts the weeps below grade or behind something. The flashing now drains into the soil against the foundation.
5. Insect screens pushed in too far. Harmless if they are vents; a wad of steel wool jammed to the back of the cavity is a plug.

If you want the bugs out, buy weep vents. A few dollars each, they press into the open joint, and a new wall gets them anyway; they are in the brick rate.

How to tell whether your wall has flashing at all

You cannot see flashing from outside, but you can usually see where it is not. Walk the bottom course: no weeps anywhere on a house built after about 1980 means there is probably no flashing either, because a mason who installs one installs both. Look over the windows for the same thing. Inside, a stain or soft drywall at the bottom of an exterior wall or under a window, with nothing wrong above it, is the cavity draining into the house.

The honest test is a hose and twenty minutes. Run it on the wall above a window, not at the window, and watch the weep course under the lintel. Water coming out of the weeps is a wall doing its job. Nothing coming out while the inside wall goes damp is a wall that needs the next section. Chimney and wall flashing leaks is the roofing side of the same problem.

What fixing it costs

Weeps filled, flashing fine. A grinder and a half day to open the joints and set vents. It is a masonry call at the $3,500 minimum job if you hire it, or a Saturday with a hand grinder, safety glasses and the patience not to cut the brick above. Either way it is cheap next to what it prevents.

No flashing over the windows. Retrofitting a through-wall flashing means taking out the course of brick above the lintel in sections, slipping the flashing in behind the membrane, and relaying the course with weeps. Price it as brick removal at $9 a square foot and brick relaid at $36 on the area that comes out, plus the minimum: a 6 ft window with a 1 ft course over it is 6 sq ft, $54 to remove and $216 to relay, and you are paying the $3,500 minimum for the day either way. Six windows in one visit, 36 sq ft, is $324 and $1,296, $1,620 of brick work, and the minimum still governs. One window is a $3,500 job and six windows is the same $3,500 job, so do the wall, not the window.

No flashing at the base, wall wet inside. The bottom course comes out in sections, flashing goes in over the ledge and up behind the membrane, the course goes back with weeps. On a 40 ft wall that is 40 sq ft, $360 to remove and $1,440 to relay, $1,800 of masonry, so the $3,500 minimum, plus whatever the sill plate and the drywall inside need. A whole-house base-flashing retrofit on 160 ft of perimeter is about 160 sq ft, $1,440 to remove and $5,760 to relay, $7,200 before HST, $8,136 with. That is a lot of money for a line that cost nothing when the house was built, and it is the argument for watching the mason on the first course.

The air space full of mortar. No fix short of taking the wall down. Which is why a new wall gets a mortar net or a drainage mat in the bottom of the cavity, and why you check it before the fourth course goes on.

What to look at on a new brick wall before it gets too high to see

1. The base flashing is in before the first course, up the wall behind the membrane at least 6 in., out over the front edge of the ledge, lapped at the joints, turned up at the ends. Photograph it with a tape.
2. Weeps in the first course, every third brick or so, open or vented. Count them against the length of the wall.
3. The air space is clear. Look down into it from the top of the second or third course: no mortar bridges, no droppings on the flashing. A mortar net or mat down there is a good sign.
4. Flashing and weeps over every lintel and on every shelf angle, turned up at the ends so the water does not run off the end of the flashing into the cavity.
5. Ties into the framing or the ICF webs on the spacing the code and the brick maker want, not into sheathing alone. Support and ledges covers the ties and the ledge.

Those five are the whole difference between a brick house that is dry for a century and one that is damp from the first spring. The brick is the same; the cost is the same. The wall protection hub covers the second plane of protection behind every cladding, not just brick, and stone veneer problems is the adhered-stone version of this page.

Questions people ask

Sources and further reading

• Ontario’s Building Code, Section 9.27 Cladding: the first and second planes of protection, sheathing membrane, flashing at openings and transitions, and the clearances from grade and roofs that every siding and stucco job has to meet.
• Canada Masonry Design Centre: masonry veneer support, shelf angles, weep holes, through-wall flashing and air space, in Canadian terms.
• Canada Mortgage and Housing Corporation: the Canadian wall-assembly and moisture research behind rainscreens and the second plane of protection.