Before you compare brands or glass packages on a replacement project, there's an earlier decision that shapes everything after it: how the new window gets installed.
There are two methods. Both are legitimate, both pass inspection, and they produce very different results in appearance, waterproofing, and what can actually be specified. Most homeowners never hear the distinction explained, which is a problem, because it's the decision that determines whether you inherit the previous window's waterproofing or start clean.
What is a retrofit window installation?
In a retrofit, the existing window frame stays in the wall. The old sash and glass come out, the frame is cut back, and the new window is set into that opening and patched in. The stucco, siding, and interior finish are left largely undisturbed.
Two things to consider.
The new window almost always has to be custom sized. You're fitting into an opening whose dimensions were fixed decades ago by the frame that's still there. Those dimensions rarely match a standard size, and you have very little flexibility to adjust. Every unit gets built to the opening rather than pulled from a size chart.
You also inherit the old window's waterproofing. This is the part worth understanding clearly. The weather barrier and flashing that protect the opening are behind the existing frame, which is staying. The new window doesn't get new waterproofing. It relies on what's already there.
If that existing waterproofing has failed, or if there's an active leak, dry rot, or damaged flashing behind the wall, a retrofit installation conceals it rather than resolving it. You typically won't discover the problem until after the new window is in and the damage has continued.
None of this makes retrofit wrong. It's a completely valid method, it passes inspection, and on a sound wall with no moisture history it's often the sensible choice. But it should be a decision, not a default you weren't told about.
What is a new-construction window installation?
In a new-construction replacement, the wall is opened and the entire existing window comes out, frame included. The new window is installed directly to the wall studs, new flashing and weather barrier are integrated properly, and then the wall is rebuilt and finished.
The wall and the finish around the opening are disturbed, and the work is more involved. In exchange:
- The waterproofing is new. Flashing and weather barrier are installed correctly around the new unit rather than inherited from whatever is behind the old frame.
- Any hidden damage becomes visible. If there's dry rot or a failed barrier, you find it while the wall is open, when it's straightforward to repair.
- The opening size can change. You aren't locked to the old dimensions, so you can enlarge an opening, change proportions, or reconfigure the elevation.
- You get the full frame. Because you aren't fitting a window inside an existing frame, more of the opening stays glass rather than frame.
That last point is worth dwelling on. A retrofit places a new frame inside an old frame, and the visible glass shrinks accordingly. On a large opening the difference is modest. On a smaller window it can be noticeable, and on a run of windows across an elevation it can change how the whole facade reads.
Which method is right for my project?
Retrofit tends to make sense when:
- The existing frames are sound with no history of leaks or moisture
- You're keeping the same opening sizes
- The exterior finish is intact and you'd rather not disturb stucco or siding
New construction tends to make sense when:
- There's any history of leaking, staining, or suspected dry rot
- You're changing opening sizes or reworking the elevation
- The stucco or siding is being redone anyway
- You're changing material or style in a way that needs a different frame depth
- You'd rather do it once, correctly, with no inherited unknowns
On the Westside specifically, the housing stock matters. Brentwood, Pacific Palisades, Santa Monica and Bel-Air have a great deal of mid-century and older construction where the original waterproofing is well past its service life. On those homes, a retrofit can quietly carry an existing problem forward for years.
Do replacement windows need to meet Title 24?
Yes. Replacement windows in California have to satisfy Title 24 energy requirements, and the values are set by your project's climate zone.
This catches people out on the Westside, because the zones aren't uniform. Brentwood sits in Climate Zone 6, while Beverly Hills is Climate Zone 9, and they're about a mile apart. Our guide to knowing your windows meet Title 24 covers what U-factor and SHGC measure and how the targets are set.
Installation method doesn't change the energy requirement, but it does change what's practical. Custom-sized retrofit units still have to hit the same numbers as anything else.
What about the window itself?
The installation method and the window are separate decisions, and they're best made in that order. Once you know whether you're going retrofit or new construction, the material and brand conversation gets much simpler, because the method constrains frame depth, sizing, and sometimes which lines are even available.
If you're at that stage, our guide to choosing a window brand works through style, then material, then brand.
Talk it through at a showroom
Which method is right for your walls is a conversation with your contractor or architect. What we can tell you is what each method means for the window itself, because that's what we build with the manufacturer.
Retrofit means custom sizing to an existing opening and a narrower set of frame options. New construction opens the full range, including changing the opening. Once you know the method, we can specify the right product for it.
Bring your address, photos of the existing windows inside and out, and the method your contractor is planning. Showrooms in Brentwood, Irvine, San Diego, and Santa Barbara, by appointment.
Common questions
What is the difference between a retrofit and a new-construction window installation?
In a retrofit, the existing window frame stays in the wall and the new window is fitted into it, leaving stucco and interior finish largely undisturbed. In a new-construction installation, the wall is opened and the entire old window including its frame is removed, the new window is attached to the studs with new flashing and waterproofing, and the wall is rebuilt.
Do retrofit windows have to be custom sized?
Usually yes. A retrofit window is fitted into an existing frame whose dimensions were set when the house was built, and those dimensions rarely match a standard size. There is very little flexibility to adjust the opening, so units are typically built to measure.
Does a retrofit window installation include new waterproofing?
No. The flashing and weather barrier sit behind the existing frame, which stays in place during a retrofit, so the new window relies on the existing waterproofing. If that has failed or there is an active leak, the problem is generally not discovered until after installation.
Is retrofit window installation up to code?
Yes. Retrofit is a valid installation method and passes inspection. It is often the right choice on a sound wall with no history of moisture problems. The tradeoff is that it depends on existing waterproofing rather than replacing it.
Do replacement windows need to meet Title 24 in Los Angeles?
Yes. Replacement windows must satisfy Title 24 energy requirements, and the targets depend on your climate zone. Brentwood is in Climate Zone 6 and Beverly Hills is in Climate Zone 9, so nearby addresses can be held to different values.