Throughout my time as a forensic architect, I have seen a lot of buildings fail due to poorly installed brick veneer. While brick is an extremely durable and water-tolerant cladding material, it cannot overcome poor workmanship and poor detailing. It certainly is not waterproof, and care must be taken to protect the structure behind the veneer. Unfortunately, I don’t see this care on the projects I visit. (Of course, I wouldn’t be on a project if something wasn’t wrong.) Again and again I see the same mistakes made, many of which lead to very expensive callbacks.
In this article, I’ll share what I’ve learned in my forensic work, beginning with some of what doesn’t work. Seeing the results of doing things the wrong way helps to explain why the details I advocate as best practice are worth doing in the first place, even if they seem a bit excessive at first.
How Brick Veneer can Fail
Rarely does the brick installation itself fail. Laying up a flat wall with straight, even courses and raking the mortar joints is often done well. The challenge is making sure that the brick is supported properly, that it’s securely tied to the structural wall, and that the proper moisture-control measures have been taken to ensure that moisture won’t affect the wood framing behind the brick veneer.
Modern brick fired at high temperatures can be fairly water-resistant. Older bricks are typically more porous and will absorb a surprising amount of water. But regardless of the type of brick, water will find its way through the cladding.
For starters, there are all the common leak spots, such as roof and wall penetrations and (of course) windows. In addition, mortar joints in a brick wall tend to leak. Mixing mortar introduces tiny air bubbles. Once troweled on, the water in the mix evaporates, leaving even more holes, as well as lots of hairline cracks between the mortar and the brick. Wind-driven rain will soak the wall, and as the moisture moves from wet to dry and warmer to cooler, the back of the brick will eventually get wet—you can count on it.
THROUGH-WALL FLASHING FAILURES
On a surprising number of the brick projects I am called in to investigate, the failure stems from a lack of proper through-wall flashings.
A classic example of a detail that often fails is counterflashing installed where a sloped shingle roof abuts a brick wall. The metal is usually 4 or 5 inches high and follows the slope of the roof. The flashing shown here has simply been let into a saw kerf in the brick and held in place with caulk or the occasional nail wedged between the metal and the brick. Inevitably, the flashing falls out of the wall, and then it offers no help whatsoever.
Similar meager attempts were made to flash a chimney, a headwall, and a gable-end parapet wall. All used saw-cut flashings that provided little protection from water flowing down the roof and zero protection from rain soaking the wall above the flashing.
Any water that gets behind the brick will be headed right down into the framing and the interior finishes, as I’ve illustrated above for one wall repair. A proper through-wall flashing (shown as the “proposed wall repair”) must run from under the weather-resistive barrier on the structural wall and extend all the way through the brick to the exterior; anything short of meeting the front face of the brick is much less effective at getting the water out.
Weep holes
Through-wall flashing works in concert with weep holes to gather the water that leaks past the brick face and give it a path to drain safely away. According to the Brick Industry Association (BIA), weep holes should be placed every 24 inches on-center (or every 16 inches when cotton rope is used as a wick).
I would rather see a wall with good through-wall flashing and too few or even no weep holes than a wall with weep holes and no or poorly installed through-wall flashings. Even if there are no weep holes, when there is a proper through-wall flashing that terminates on the face of the wall, the collected water will eventually evaporate or escape through the tiny cracks in the mortar before it can damage the framing. But without through-wall flashing, weep holes won’t do much of anything.
STEPPED PAN FLASHING
Admittedly, installing through-wall flashing correctly, particularly on a sloped roof-to-wall intersection, involves a detailed process and requires close coordination between the roofer and the mason. As painstaking as this can be, it’s the only way to prevent water from seeping into the living space below.
Stepped pans. Executing a true through-wall counterflashing along the rake of a sloped roof requires installing a series of stepped pans. On the job shown above, the masons began by building up the brick in stair-step fashion. The rise and run of these stair steps will vary with the pitch of the roof, but each step will be the same because the slope stays the same and the brick coursing is the same.
Next, the masons laid in copper pans. A key feature of these pans is the soldered end-dams that direct water onto the front edge of the pan.This edge laps over the front of the brick about 1/2 inch, providing a lip to which the counterflashing will be attached.
On this particular job, we had been called in because of the severe cracking of the brick across the entire gable-end wall. All of the unpainted brick shown was removed. We discovered that only three brick ties had been installed high up on the wall near the gable vent. There were no brick ties whatsoever across the entire area below it. It was lucky that this wall had not come down entirely.
When we replaced the brick, we included the stepped pan flashings where the sloped roof joined the gable-end wall (at left behind the railing in photo 9 above; the railing was removed for the demolition phase).
When everything had been cleaned up from laying the new brick, copper skirts were slid up under the front edge of each pan and pop-riveted or screwed in place. These copper skirts serve as a counterflashing to the stepped L-flashings that the roofers wove in with the new roof shingles.
Two-Layer WRB
While the lack of brick ties caused the initial failure on the gable end, when we took the brick down, we discovered a number of other flaws. The most glaring was a combination of excessive mortar squeeze-out on the back surface of the brick, along with a very cheap and poorly installed weather-resistive barrier.
A single layer of housewrap provides almost no barrier to water when mortar comes in direct contact with it. Water that leaks behind the brick wicks along the excess mortar to the face of the WRB and then seeps right through, wetting the wood sheathing.
Cavity or not. Currently, building codes require a minimum 1-inch air space between the brick and the structural wall. (This requirement could be challenged when you’re using some of the newer self-adhesive or liquid-applied WRBs in tandem with a drainableinsulation, such as mineral wool. See “ Challenging Tradition”.)
In theory, this space provides a drainage path and enough space to keep mortar, and any water it holds, safely away from the WRB that guards the wall sheathing.
In practice, however, that gap is not enough to always keep mortar at bay. On a recent job, one mason proved this point. Right around the corner on the same building, a different mason did a much better job of keeping the cavity clear. This variation in workmanship is inevitable and is why I insist on a double-layer WRB.
Asphalt felt plus a drainable wrap. In my opinion, brick—like stucco—should be installed over two moisture barriers, as shown in the detail illustrations on the facing page. I like to see a layer of #30 asphalt-impregnated organic felt covered with a “drainable” housewrap, such as Tyvek StuccoWrap or CommercialWrap D. Both of these wraps are “crinkled” to create a textured surface, which forms channels that help drain water down the face of the WRB.
There are several other textured building wraps on the market. Steer clear of woven building wraps. These abrade easily and the holes between the woven filaments don’t do much to keep water out. I recommend choosing a commercial-grade WRB, which will be a little more resistant to abrasion and UV exposure. Durability is key in any working environment where masonry is being used.
The more durable building wrap will protect the asphalt felt from the sun during construction. It acts as a first line of defense against any moisture that leaks past thebrick. The felt is there as protection against any moisture that seeps through the building wrap, as it will at every transfer point where mortar slops against the WRB.
Window and Door Flashing
Ideally, window and door head flashing would be fabricated out of metal and formed with end dams, similar to the stepped pans for roof-to-wall intersections. Membrane flashings that extend to the exterior will eventually weather and deteriorate. But even if a membrane flashing is used and it extends well past the side of the window, it can work.
In the example shown, you can see the rusted angle going across the top of the window. The membrane over it extends beyond the sides of the rough opening and comes out the exterior face of the brick. Provided the membrane laps under the WRB, this is a serviceable attempt to keep water off the head of the window. The problem, of course, is that it looks bad.
A good alternative to membrane flashing is a thin copper sheet laminated to waterproof Kraft paper. Two sources are York Manufacturing and MasterCraft Metals. Because the copper is thin, it’s not too noticeable on the face of the brick. It doesn’t shrink, and it withstands the compression of the masonry and resists the acids and alkalis in mortar. This material can be turned up to make little pigs’ ears at the corners to form end dams, and the Kraft paper will protect the copper from galvanic reaction with the lintel. If you’re using a bare-copper pan flashing at the head, you will need to apply a strip of peel-and-stick over the steel before setting the copper pan.
The steel angle is for structural support only; it should not be used for flashing. Some contractors will lap the WRB over the top leg and rely on the angle alone to divert water to the exterior. More often, though, the steel is installed on top of the housewrap. (Note the brick ties, as well, in this photo. They were affixed to the sheathing but were never bent over and embedded into the mortar.)
Window sills should always be sloped at least 15 degrees, per BIA standards, and should overhang the face brick by at least 1 1/2 inches. Too often, I see flat brick sills that barely poke past the facade, providing very little positive drainage of all the water that sheets off the face of a window.
Through-wall flashing should also be placed under the sloped course of brick immediately below the window. This is meant to catch any water that makes its way into the wall cavity through or around the window.
Harrison McCampbell is a consulting forensic architect in Brentwood, Tenn., specializing in moisture-related construction defects. You can find him online at MCA4N6.com.
