Installing retrofit windows on the stucco wall is not too difficult. The challenge is to ensure that it doesn’t leak and that it looks clean and polished. If you are planning to install a new window by yourself.
Here are the steps that you must follow:
1. Assess the existing window
Identify if the window is made of wood, steel, or aluminum. The existing frame of the window will be intact while the interior portion of it will be disassembled or detached. This is to avoid dismantling the weather-resistant barrier or the wall which is responsible for protecting against moisture entering the home or property.
Since you are installing a retrofit window on a stucco wall, you should use an appropriate sealant that is compatible with the substrates. For example, Siloxa-Tek 8500 is an excellent sealant for stucco. It is also a salt repellent sealer. So if you reside in a tropical state with salts in the air, this sealer will prevent cracking, spalling, and pitting.
2. Measure the opening
From the existing window, take off the sash members and metal rails to make sure that you are measuring the narrowest point in your window. This is the daylight opening measurement. Get the daylight opening width measurement at three angles – top, middle, and bottom. Afterward, get the height measurement in three angles – left, middle, and right. When you have the narrowest width and height measurements, subtract ¼ from each to get the “net frame size” for ordering.
Once the new retrofit window is installed, its flush fin will lay perfectly flat against the existing window frame and stucco. Check closely if there’s any part that extends past the stucco or siding. If there’s any, cut way such excess parts. Hinges and drip legs before installing.
3. Inspect the window prior installation
If there is any damage to the window frame joining seals, it must be repaired. The sill track should be able to hold water without leaking to the interior for at least 15 minutes. After the inspection, disassemble the existing window by removing the vent panel, center post, fixed panel, and any other components that will interfere with the installation. Just keep the existing frame intact.
4. Polish the exterior surface of the wall
Using a stiff bristle or brush, putty knife, scrape or grind any rough texture on the exterior surface where the flush fin of the new window will be placed. This leaves a smooth surface for installation. Don’t forget to also remove dirt from the sill track.
5. Test the retrofit window if it fits the size of the opening
Before caulking, test fit the retrofit window size if the frame matches flush against the wall or as close as possible. If there’s a gap found, try to lessen it as much as possible by using additional blocking for sill support. You can also trim the flush fin if a narrower width is needed.
6. Pre-drill pilot holes into the interior channel of the new frame
Avoid drilling into the sills. Holes must be no more than 18” apart, on center, with corner holes approximately around 6” from the end. Make sure that nothing interferes with the sash operation.
7. Put a continuous bead of sealant along the exterior perimeter of the window
Run the sealant along the exterior of the window where the flush fin connects with the wall. Leave a 2” allowance at each corner at the sill to allow any moisture to evaporate.
8. Insert the new retrofit window into the opening
Make sure that the retrofit window is level and precise by shimming the frame from the interior.
Install shims at fastener points where it is possible. Using a pan head screw, secure the window in place. You can begin from the upper jamb corners. Go over the level and shim if needed. In the opposite jamb, place an additional screw and recheck for level. If the frame is properly level, attach the rest of the screws.
9. Run a bead of sealant around the exterior edge of the flush fin
Once the window is secured, finish with sealant sound the exteriors of the flush fin. Wipe off any excess for a clean look. Meanwhile, from the interior, use a backer rod or insulation material to fill the gap between the old and the new frames. You can hide the void with flat interior trim or any of your choice. Run a bead of sealant along the edge of trim for a clean, polished look.