Retrofit Windows in Stucco and Brick Homes

A retrofit window is a new window installed inside the frame of the old one, so the wall around it is not opened up. In a stucco house the usual version is a flush-fin (also called flush-flange) window: the old sash and glass come out, the old aluminum frame stays, and the new window is set into it with a flat fin that laps over the old frame and the stucco on the outside ^{1 3}. Andersen describes these windows as fitting inside an existing frame without disturbing the exterior stucco or the interior drywall ¹.

In brick and other masonry walls, one approach is the block-frame window, which is set into the opening and fastened through its frame or with clips rather than nailed through a fin ⁴. Both methods depend on sealing done right, and the manufacturers' instructions say exactly how: that is what to ask an installer about.

Why stucco homes in the West get retrofits

Flush-fin products are aimed at homes in the Southwest with aluminum windows set in stucco walls ^{2 3}. The reason is how the old windows are attached. Pella's instructions explain that in frame construction a window's nailing fins are usually nailed to the studs, with siding, brick veneer or other exterior material applied over the fin on the outside ⁴. Taking that window out completely means cutting into the finish around it.

A flush-fin retrofit avoids that. Pella titles its procedure "pocket replacement with flush flange" for new windows in existing aluminum frames with stucco walls in arid climates ³. Andersen says its flush-fin frame option is sold in California, Arizona, Nevada and Utah, designed for contractors in Southwest market areas, for installation over an existing aluminum window frame in stucco ². Licensing rules for window contractors in those states are on our California, Arizona and Nevada pages.

The trade-off is the same as for any insert: the old frame stays in the wall, so its condition and its seal to the wall carry over. Full-frame vs. insert replacement covers when the frame has to come out instead.

How a flush-fin retrofit goes in

The manufacturers set limits before the steps. Andersen says its flush-fin units are only for openings with an aluminum frame that has a 3/8 inch wide exterior surface, are not permitted for tear-out replacements, and are not permitted in openings more than three stories above grade ^{1 2}.

The outline of the installation, as Andersen and Pella describe it ^{1 3}:

1. Measure inside the old frame. Pella measures the opening in the remaining aluminum frame after the sash and glass are removed, and says the new window must be 1/2 to 3/4 inch smaller in width and height ³.
2. Clean the old frame and open the weeps. The existing frame is cleaned of dirt and debris, and Pella says to make sure its weep holes are open and clear ³.
3. Seal the corners and fill the sill. Pella applies sealant where the jamb and sill of the old frame meet and adds wood blocking in the sill cavity, notched so the existing weeps are not blocked ³.
4. Dry fit. The window is test-fitted from outside. Pella says to confirm the flange will overlap the old aluminum frame or the stucco by at least 3/4 inch on all four sides ³; Andersen checks at this stage whether the flange needs trimming ¹.
5. Seal and set. Pella places a 3/8 inch bead of sealant on the exterior perimeter of the old frame, leaving 2 inch gaps at each weep hole ³. Andersen applies sealant to the existing frame leaving gaps at the sill for drainage, places sill shims, and checks for plumb, level and square before fully tightening the fasteners ¹.
6. Seal inside and out. Both add an interior air seal, then a bead of sealant around the exterior of the flange, again with gaps left at the sill or below each weep hole so water can drain ^{1 3}.

The gaps in the sealant are deliberate: both manufacturers leave them so water can drain out through the existing frame's weeps ^{1 3}. Andersen notes that its page is an overview and that the window's own installation instructions should be followed ¹.

Block-frame windows in brick and masonry

A block-frame window has no fin, so it does not need anything to lap over the wall finish. Pella's block-frame instructions start with full frame removal: the sash and the entire old frame come out, leaving the original rough opening ⁴. Its procedure for masonry construction with stucco then goes ⁴:

• Size. The window must be about 1/2 inch smaller than the opening in width and height.
• Wood buck. Two beads of sealant go on the masonry where a treated wood buck will be attached, with sealant at the buck's corners and where it meets the stucco; Pella notes the sealant must be compatible with the water resistant coating.
• Flashing. Flashing tape runs from the stool over the sill and up each side, and the buck gets a water resistant coating or flashing tape.
• Fastening. The window is set on shims and fastened with screws through the frame or with clips; masonry screws go at least 2 inches from the wall edge, and Pella says to use frame screws at the sill where possible so the interior seal is not pierced.
• Sealing. Interior sealant goes around the frame, with extra around the clips against air and water, and exterior sealant goes between the window and the finished wall. An optional frame expander trim can bridge the gap to the stucco, sealed at its edge too.

Because the old frame comes out, a block-frame job lets the installer see the opening, which a flush-fin retrofit does not. Pella's instructions also carry a caution that many windows in older homes are painted with lead-based paint and that removal may disturb it ⁴.

What to ask about sealing

Sealing is where a retrofit succeeds or leaks, and it is hard to inspect afterward. Useful questions for each installer:

• Will you follow the manufacturer's installation instructions for this exact window, and can I see them?
• Is my old frame aluminum, and does it meet the manufacturer's limits for a flush-fin unit ¹?
• How will you keep the existing weep holes open, and where will the gaps in the exterior sealant be ³?
• What sealant will you use, and is it compatible with the existing frame and the stucco or coating ⁴?
• How will you air seal the interior side?
• If the old frame is damaged, will you stop and quote a full-frame or block-frame installation instead?

Pella's instructions also warn that its products should not be used in barrier wall systems that do not manage moisture, such as barrier EIFS (synthetic stucco), and that in California, New Mexico, Arizona, Nevada, Utah and Colorado such installations must follow Pella's instructions ³. If your stucco might be a synthetic system, ask before you choose a method.

Cost, permits and next steps

Retrofit and full-frame prices are covered in window replacement cost and, for aluminum frames, aluminum window cost. Whether a permit is needed depends on your building department; see do you need a permit to replace windows. How to choose a window installer covers what a written quote should list. When you are ready, you can compare quotes from window installers.

We are not affiliated with the manufacturers named.

About these figures

• ¹ Reported: Andersen's overview of flush-fin replacement in stucco (installation steps, sill drainage gaps, 3/8 inch aluminum frame limit, no tear-out replacements, three-story limit), checked October 26, 2026.
• ² Reported: Andersen's April 18, 2023 announcement of its flush-fin frame option for California, Arizona, Nevada and Utah over existing aluminum frames in stucco, checked October 26, 2026.
• ³ Reported: Pella's flush flange pocket replacement instructions for existing aluminum frames in stucco (1/2 to 3/4 inch sizing, 3/4 inch overlap, 3/8 inch sealant bead with 2 inch weep gaps, barrier wall caution), revised March 31, 2023, checked October 26, 2026.
• ⁴ Reported: Pella's block-frame instructions (full frame removal, nailing fins under the exterior finish, 1/2 inch sizing, wood buck, flashing, 2 inch masonry screw edge distance, sealing, lead paint caution), revised March 31, 2023, checked October 26, 2026.