by Mike Sloggatt

I have replaced hundreds of windows in brick-veneer homes across Long Island. The coastal environment requires a little extra care, but the procedure is essentially the same for any climate. The tricky part with brick is getting the flashing in the right place.

With most window replacement jobs, the ideal installation requires the removal of the siding, which allows the window to be integrated with the existing weather-resistive barrier (WRB). In a brick-veneer structure, however, that's not so easy. Removing aged brick and mortar to access the window is certain to be noticed long after the job is done. The additional cost associated with surgical removal and the painstaking process of matching new brick and mortar is often prohibitive to most clients. So I resort to the methods described here. The procedures are a compromise, but they're a lot better than leaving an old drafty, leaky window.

Measurement Is Key

The selection of the proper window is the primary consideration in this environment. I prefer to use a "prime" window. One I use a lot is the Andersen replacement window; it can be custom sized to fit the openings perfectly, which makes all the difference. But any high-quality window with a nailing flange system will work if you can get the right size for the existing openings.

Pay attention to measuring for the new window. When the window opening is in place, the flange will be secured to the framed wall and will be recessed into the brick opening. To ensure a watertight installation, you need enough room to integrate the flashing with the existing WRB.

There are two measurements of concern here: the rough opening (RO) and the brick opening (BO). The RO is the interior dimension of the framed wall opening. This is the opening we are most familiar with when installing windows in a framed wall. The BO, on the exterior, must be big enough to give us room to maneuver with our flashing around the new window. This space will get covered with an exterior brick mold once the new window is in place.

If we're lucky enough that the existing window has a wood-frame window with a brick-mold exterior trim, the existing RO can usually be used to order the new window. The old brick mold provides the room we need to integrate the flashing. But most of the applications I see involve old metal-frame windows (usually steel or aluminum) that were mounted to the RO prior to the application of the brick veneer. The edges of the window typically come right to the edge of the BO, and the flanges are buried behind the brick. Steel-frame double-hungs, which have a spring mechanism buried in the jambs, have an even larger RO. In any of these cases, we can't use the existing RO to order new windows.

The key to a flawless window replacement in a brick-veneer wall is sizing the new window properly. The replacement unit must be small enough to fit through the existing brick opening without having to dismantle the brick and mortar, but large enough to minimize the unsupported flashing and allow the new unit to be inconspicuously trimmed out.

Instead, I first measure the BO from the exterior, then open the window and reference the available RO to the BO. The window should fit in the BO with enough room to allow at least 1 1/4 to 1 1/2 inches on both sides of the window (Figure 1) and a minimum of 3/4 inch on the top. It may be necessary to pack out the old RO to create an opening that is this much smaller than the BO. Ideally, I like to have 2 inches on the bottom, too, but I rarely get that and will settle for less if necessary.

Figure 1. Minimum Opening Sizes

The window should be sized to fit in a rough opening (RO) in the framed wall that's at least 11/4 to 11/2 inches smaller than the brick opening (BO). Ideally, this BO would also be 2 inches higher than the RO to allow room at the head and sill, but the window can still be made to fit through a smaller BO if the bottom flange is removed before it's installed.

Integrating New Flashing and the Existing WRB

Almost every job I have done has had No. 30 felt or building paper over the framed walls as a WRB. When removing the old window, care must be taken to preserve the integrity of this existing WRB. After a number of years it can become dry and brittle, so we have to be gentle to keep from tearing it up when working the opening.

Once the old window is out, we focus our attention on preparing the opening, using a metal sill pan and flexible flashing, as outlined in Figure 2. It's important to use a sill pan that gives you an upturned edge on the inside to block water draining to the interior, and to lap the flashing over the pan so water draining from higher up will be caught by the sill pan (Figure 3).

Figure 2. Flashing Under Brick Veneer

Step 1:

Install flashing tape over the RO sill. Let approximately 2 to 3 inches of the flashing lap over the brick sill. Then, using a taping knife, push the flashing down between the brick and the existing WRB. Step 2:

Install a mechanical sill pan over the flashing tape. The author prefers a metal pan — copper or (better yet) lead-coated copper. Even vinyl will suffice, as long as it will keep the water flowing to the outside. This pan should have a turned-up edge on the inside to create a dam to prevent water flowing inside and a turned-down edge on the outside. Step 3:

Cover the side jambs of the RO with two strips of flashing tape. To do this, the author first slits the paper on the back-side cut about 2 inches from one edge, then peels off the backer on the wide side, using the exposed tape to cover the RO jambs. This leaves the 2-inch section to stand straight out of the opening. The author then peels off the remaining backer paper and uses a taping knife to push the tape back behind the brick, where it can adhere to the WRB. Step 4:Here is the tricky part. Fabricate a top flashing that will slip behind the existing WRB, and go over the top of the new window, allowing for any trim that may be installed. Using a taping knife, carefully work the WRB away from the sheathing. The goal is to separate it from any fasteners without tearing it up. Once this is done, slip the flashing between the WRB and the sheathing. You may need to use some flashing tape to hold this in place.

Figure 3. The author uses a metal brake to form a copper pan (left). All windows eventually leak, but the pan will capture the water and allow it to drain to the exterior. The inside of the pan should have an upturned edge to prevent the water from draining to the interior, and the side flashings should lap over the ends of the pan (above).

In some cases, however, there is not enough of a space behind the brick to push the flashing tape back there. Or, the mortar that squeezed out on the back side of the brick has clogged the space. This squeeze out may be chipped away at the edges, but if it's really heavy, even that won't be enough to provide clearance for flexible tape. In this case, I bend four aluminum or copper L-shaped strips, as shown in Figure 4. At a minimum, the legs of these L-strips should be 2 inches, but a 3- to 4-inch leg is preferable. Remember: The farther the water is deflected by the flashing from the edge of the BO, where the most water is likely to get blown in, the less likely the water will find its way back into the RO as it drains down the wall.

Figure 4. Alternative Side Flashing If flexible flashing can't be pushed behind the brick at the sides of the window opening, the author bends four copper or aluminum L-strips to use as side flashing instead. To install these, he starts with the bottom piece, which is as long as at least half of the height of the window and has a flap that allows the end to slide down below the sill height. The second piece extends to the head, with a flap that reaches about 2 inches above the window opening and is long enough to lap over the first piece installed.

Installing the Window

Once the sides and the sill have been wrapped, it's time to install the window. If the BO is tight, we may need to trim back the window flanges. I often have to completely remove the bottom flange to get the window in, as well. A jigsaw works for trimming off a formed vinyl flange. On some windows, it's possible to pull the flange extrusion out of the frame, or it may require careful trimming with snips and a utility knife.