Every window replacement in the San Gabriel Valley starts with one question the homeowner rarely knows to ask: does the old frame stay, or does it go? That is the whole difference between retrofit windows and new-construction windows. It decides whether the crew shows up with a caulk gun or a stucco saw, whether the job takes an hour per window or half a day, and whether you need a painter afterward. Get it right and replacement is a clean, quick upgrade. Get it wrong and you either pay for tear-out you did not need or put a new window into a frame that was never going to hold it.
We have installed both kinds across Glendora, La Verne, San Dimas, Claremont, Covina, Azusa, Pomona, and Upland since 1989 — 36 years, family owned. Here is the plain-language version of what each install involves and how we decide which one a house needs.
The short version
Retrofit (also called insert or replacement) windows fit inside your existing frame; nothing on the exterior wall is disturbed. New-construction (full-frame) windows remove the old frame entirely and attach to the house framing with a nailing fin, which on a stucco house means cutting the stucco back and patching it. Most sound SGV stucco homes qualify for retrofit. Rot, water damage, a badly out-of-square opening, or a change in window size push you to full-frame.
What the two terms mean
A window is really two parts: the frame that is fastened to the house, and the sashes or panels that hold the glass. Both kinds of replacement give you an entirely new unit — new frame, new glass, new hardware. The difference is what happens to the old frame.
- Retrofit windows (insert, replacement, or “Z-bar” windows) are built to slide into the opening left by the old sashes. The old frame stays in the wall and the new window is sealed to it. On the exterior, a flange or Z-bar covers the joint, so the stucco and trim are untouched.
- New-construction windows (full-frame or nail-fin windows) are what a builder installs in a brand-new house. A thin fin around the perimeter nails to the framing under the exterior finish. Using one in an existing home means removing the old frame, cutting the stucco or siding back to expose the studs, installing and flashing the new window, and then patching the exterior.
If your home is one of the mid-century ranches or 1970s–80s tract houses common from Glendora to Upland, you almost certainly have aluminum frames set in stucco. That combination is exactly what retrofit windows were designed for, which is why they dominate replacement work here. (If you are still deciding whether to replace at all, start with our guide to the seven signs it is time for new windows.)
How a retrofit install works
The crew removes the old sliding panels and any interior stop, cleans the existing frame, and dry-fits the new window. A bead of sealant goes on the old frame, the new unit is set and shimmed square, it is screwed through the frame into the jambs, and the exterior flange is sealed against the stucco. Inside, a small trim or caulk line finishes the joint. A straightforward slider takes roughly an hour; a whole house is typically a one-day job.
What you give up is a small amount of glass area. Because the new frame nests inside the old one, each side loses a strip roughly the width of the new frame. On a big living-room slider you will not notice. On a narrow bathroom window, you might. Retrofit also depends entirely on the old frame being sound and reasonably square: the new window is only as good as what it is fastened to.
How a full-frame install works
Full-frame replacement starts by cutting the stucco back several inches around the opening to expose the original nailing fin and the framing. The old window comes out completely. The opening is inspected, any damaged framing or sill is repaired, new flashing and building paper are integrated with the wall’s weather barrier, and the new-construction window is nailed and sealed in place. Then the stucco is patched, cured, and painted to match, and the interior drywall or trim around the opening is repaired.
You get back the full original glass size, a brand-new weather seal all the way through the wall assembly, and the freedom to change the window’s size or shape. The cost is more labor, more trades (stucco, paint, sometimes drywall), and a longer timeline. It is the right call when the opening itself is the problem — not just the window in it.
Retrofit vs. new-construction windows side by side
| Factor | Retrofit (insert) | New construction (full-frame) |
|---|---|---|
| Old frame | Stays in the wall | Removed completely |
| Exterior stucco | Untouched | Cut back and patched |
| Glass area | Slightly smaller | Full original size (or resized) |
| Time per window | About an hour | Several hours, plus patch and paint |
| Extra trades | Usually none | Stucco, paint, sometimes drywall |
| Weather sealing | Sealed to old frame | New flashing tied into the wall |
| Cost | Lower | Higher, driven by labor and finish work |
| Best for | Sound, square frames in stucco | Rot, damage, resizing, or failed openings |
The four things that decide which one you need
1. The condition of the existing frame
This is the big one. Aluminum frames rarely fail structurally, so a clean aluminum frame in stucco is a retrofit candidate almost every time. Wood frames are a case-by-case call: press a screwdriver into the sill corners and the bottom of the jambs. Solid wood means retrofit is on the table; soft, punky, or crumbling wood means the frame cannot carry a new window and full-frame is the honest recommendation.
2. Evidence of water damage
Staining on the drywall below a window, bubbling paint at the sill, or a soft spot in the wall means water has been getting past the old frame. A retrofit would seal the new window to a frame that is already leaking around its edges — it hides the problem rather than fixing it. Those openings need to be opened up, dried, repaired, and re-flashed. Our post on common window problems in older Glendora homes covers what that damage usually looks like.
3. Whether the opening is square
Houses settle. A frame that is out of square by more than a shim can absorb will leave a retrofit window binding on one side and gapping on the other. We measure diagonals on every opening; a small difference is normal, a large one is a full-frame conversation.
4. Whether you want a different size or style
Retrofit windows match the existing opening, full stop. If you want to turn a small kitchen slider into a bigger picture window, convert a window to a door, or shrink a bathroom window for privacy, that is a full-frame job because the framing itself changes. (If you are choosing between styles, our guide to slider, hung, and casement windows walks through what fits where.)
A common mix
Whole-house jobs are often both. A house might take retrofit windows in every bedroom and a full-frame replacement at the one window over the kitchen sink where years of splashing rotted the sill. There is no rule that says one method per house; the right answer is per opening.
What this means for SGV homes
Because so much of the housing stock from Glendora through Upland is single-story stucco with original aluminum frames, retrofit windows are the default here, and for good reason: the exterior stays clean, the job is fast, and the energy upgrade is the same. Going from original single-pane aluminum to dual-pane Low-E glass is where the comfort and utility-bill difference comes from, whichever install method delivers it. Our guide to converting single-pane to dual-pane windows covers what that upgrade changes day to day, and our post on whether energy-efficient windows pay off in this climate puts the numbers in perspective.
Bedrooms deserve one extra note. Building code can require that a bedroom window provide a certain opening size for emergency escape, and a retrofit’s slight reduction in opening can matter on an already-small window. It is a straightforward check we do at the measure, and your city’s plan checker has the final word.
We do not publish a flat per-window price because frame material, glass package, size, and the retrofit-or-full-frame call all move it. What we will do is tell you plainly at the free estimate which openings qualify for retrofit, which do not, and why — and you are welcome to request that estimate online or call (626) 335-2900.
Quick answers
Are retrofit windows as good as new-construction windows?
The window itself is usually identical. The difference is the install: a retrofit fits inside the old frame and relies on that frame being sound, while a full-frame install removes everything back to the framing. Done on the right house, a retrofit performs the same and lasts as long.
Do retrofit windows make the glass smaller?
Slightly. The new frame sits inside the old one, so you typically give up a small band of glass on each side. On most sliders it is not noticeable. On a small bathroom window it can be, which is one reason a shop might steer you toward full-frame there.
Can you retrofit a wood-frame window?
Often, yes, if the wood frame is solid and square. If there is rot, soft spots, or the sill is failing, the old frame cannot support the new window and a full-frame replacement is the honest answer.
The bottom line
Retrofit windows keep your old frame and your exterior intact; new-construction windows replace everything back to the studs. On a sound, square, stucco-set frame, retrofit gives you the same new window with a fraction of the disruption. Rot, water damage, a racked opening, or a size change are the reasons to go full-frame — and the reasons to be wary of anyone who never mentions the difference.
Glendora Window has installed new windows both ways across the East San Gabriel Valley since 1989 — 4.8 stars across 160+ verified reviews and 50,000+ jobs completed. Homeowners from Glendora to Upland can request a free estimate or call (626) 335-2900, and we will tell you which install each window needs before anyone picks up a saw.
