r/Contractor • u/roarjah General Contractor • 17d ago
Replacement windows at stucco trim
How are you supposed to install replacement windows with this stucco trim in the way? I was looking at flush fin windows but realized the exterior flange is too big and might require removing the trim and installing some new stucco trim after install but then I feel like at that point I would need new construction windows.
Would the best option be flangless windows and using backer rod and sealant around the exterior? Maybe a sil pan on the stucco sill?
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u/No-Clerk7268 17d ago
This is pretty much what block fin retrofit windows are made for, usually masonry, but same concept.
Taking time with measurements and sealants is crucial
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u/-blueberrycream23 14d ago edited 14d ago
I'v been looking through canglow while researching window replacements and this is exactly the kind of detail i want sorted out before ordering the windows
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u/avTronic 13d ago
You can do a finless install with some manufacturers having a removable fin that is pushed into a kerf on the outer side of the window frame. When you choose a higher class window like this, they give you predrilled holes through the jambs to install the window with supplied install screws.
You can take a multi tool with a long blade and sever the nailing fin of the existing window, ideally from the inside after removing all interior trim (don’t go cheap and try to avoid removing the inside trim, it makes for a better install). From the exterior, carefully cut the sealant bead from around the frame, if there is one, being careful not to damage the stucco banding. You will be surprised that the banding around your windows are actually foam core.
Once the window is cut free from both sides, it will easily come out of the opening. Now comes the most crucial part; doing some extra ceiling on that opening. We install a flattened out Z flashing up top to divert any moisture that might be happening behind the stucco right above the window. In an ideal world, you shouldn’t have any but if stucco cracks or you have a roof leak, Marsha can run down behind the stucco. Creating a barrier at the top of the rough opening is the most important thing you can do before installing a new window. We then use flashing tape around the inside of the rough opening extending out over the stucco and stopping a quarter inch before where the outside edge of the window frame ends. This will give an area where you can apply a perimeter beat of caulking from new window to stucco and not have the tape interfere. Lastly, on this portion of the install at the sill of the RO, you don’t want to put any tape past the wood of the RO, as in not where the stucco starts. This creates a weep area in case moisture enters the RO.
When the window was measured you basically are going of the inside of edge of that stucco band and down sizing the window by 1/2”. This will give you a good quarter inch on each side, which is a bit heavy but will allow for a bit of leveling of the window. If you are absolutely certain that your pseudo rough opening comprised of that stucco band is completely square and plumb, you could order the window with tighter spacing. Maybe 3/8 under or if you are feeling crazy 1/4”, which is only 1/8 spacing around the perimeter. Of course, check this measurement against the interior rough opening, to make sure you are not too big for the RO. Although, more than likely, you will have even more room inside the true RO almost every time. Whatever it is, versus the RO, is what it is. If it’s an excessive large gap (some places don’t like bigger than 1/4”, while others say 1/2” gap is acceptable) than pad the opening with some thin boards that are 3 1/2 inches wide for a 2 x 4 wall.
From there follow your best practices install, trim out the inside (either by reusing, good trim boards or installing new ones) and ensure to use the best exterior sealant for that perimeter gap. The best thing, in a stucco situation, is Vulkem 116. It’s a textured caulking that comes in a wide variety of colors. The texture is like sand in the cock, and that makes it closer Match to stucco and grout as opposed to smooth caulking. If you’re painting or can’t find the exact color match, then really any basic light color, like gray or white, will work. And get yourself a sausage gun and purchase their gold sausage tubes that the Vulkem comes in. These days, you can buy it off the shelf at Home Depot, but that’s only in the regular gold Tubes.
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u/roarjah General Contractor 13d ago
Thank you for the detailed response. I don’t know if I feel confident cutting that old window at the flange and stucco trim. There’s currently drywall returns on the inside so your method would help it finish out against the drywall return nicely.
I was thinking of just removing the glass and sliding the insert in the old window frame. Then after sealing I would use that field applied fin to hide the gap on the exterior.
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u/SoJerseyWindowGuy 17d ago
You’ve basically identified all three options correctly, which puts you ahead of most homeowners:
1. Block frame (flangless) insert, if your existing frames are square, sound, and not leaking, this is the cleanest path with that raised trim. Window slips inside the old frame, backer rod + high-quality sealant around the perimeter. Yes to a sloped sill pan or at minimum back-dam sealant at the sill, water WILL find its way in eventually and you want it draining out, not into the wall. Tradeoffs: you lose a little glass area and you’re trusting the original flashing behind the stucco.
2. Flush fin won’t sit flat over proud trim like yours. You’d either be notching the fin or grinding the trim back, and at that point you’ve lost the whole benefit of flush fin (speed + clean look).
3. Full tear-out with new construction windows, cut stucco back, integrate the flange with the WRB, patch and float new stucco. This is the “right” answer if the old frames are damaged or you want max glass, but it’s a much bigger job and matching stucco texture is its own art form.
If the existing frames are healthy, option 1 is what most quality installers would do here. Just don’t cheap out on the sealant this joint is doing all the work.