What’s a True Divided Lite on A Historic Window?
Introduction: The Pane Truth About Historic Windows
If you’ve ever looked at a grid window and wondered, “Are those little panes real?”—you’re not alone. Today’s mass-produced windows often fake the funk with stuck-on muntins and sandwich-glass simulations. But historic windows? They did it the hard way—one pane at a time, held together by a delicate framework of art and joinery known as true divided lites.
In this blog, we’ll break down what true divided lites are, how to tell the difference, why they matter, and what your options are when restoring or replicating historic sashes.
What Is a True Divided Lite (TDL)?
A true divided lite window features:
Multiple individual panes of glass (called “lites”)
Separated by wood muntins (those narrow bars you see in the grid)
Held in place with glazing putty and points
Unlike modern “grids between glass” (GBG), which simulate divisions with a plastic strip trapped between two sheets of double-pane glass, TDL windows are the real deal—beautiful, breathable, and historically accurate.
Anatomy of a Historic Muntin
Muntins in historic windows aren’t just decorative—they’re functional. They:
Support individual glass panes (typically 6, 8, 9, or 12 per sash)
Add rigidity to the sash frame
Provide beautiful shadow lines that change with the light
Common profiles include:
Ovolo (rounded edges—very popular in Federal and Georgian styles)
Putty bead (chamfered edge into the glass)
Knife-edge (sharp profile, common in early 18th-century homes)
Each region and era had its own muntin style. At Austin Historical, we can often date a window’s original build within a 10–15 year range just by examining the muntin shape and profile width. It's architectural forensics at its finest.
Why True Divided Lites Matter
1. Architectural Authenticity
You can’t fake real muntins—not up close. Replacement windows with snap-on grids or internal grills never look quite right, especially in a home that predates sliced bread.
2. Historic Tax Credit Compliance
Many local, state, and federal preservation tax credit programs require retention or replication of true divided lite windows. Fake muntins won’t cut it with your local historic review board.
3. Better Repairability
If one pane breaks in a true divided lite sash, you replace that one—rather than replacing the entire sash or insulated unit. It’s practical, sustainable, and budget-friendly.
Restoration: To Save or Rebuild?
When evaluating historic windows, we always assess:
Condition of the muntins (are they sound or rotted?)
Integrity of the joinery (mortise & tenon connections)
Glass stability (are the panes loose, cracked, or missing?)
If the muntins are in good shape:
We’ll remove failing putty, rebed the glass, and reglaze with Austin Glazing Putty
We’ll preserve as much original material as possible
If rotted, we patch with Abatron epoxy or splice in matching wood
If the sash is too far gone:
We replicate using Accoya for painted sashes (50-year warranty) or Red Grandis if the sash will be stained
We mill matching muntin profiles, lite counts, and joinery methods
We use restoration glass or salvaged wavy glass to retain authenticity
How Many Lites Is Too Many?
There’s a practical reason early windows had smaller panes: glassmaking limitations. Large, flawless sheets of glass weren’t available until the late 1800s. So, early windows might have 12-over-12 lites, while post-1900 homes moved toward larger 1-over-1 styles.
Knowing what’s appropriate for your home’s era is key to getting restoration right. Our Historic Preservation Advisors (HPAs) always consult style guides and architectural surveys before recommending muntin layouts.
Simulation Isn’t Always a Sin (But Be Careful)
There are modern window manufacturers who make simulated divided lite (SDL) windows with external wood muntins and interior spacer bars to mimic the look of true divided lites. They’re better than nothing—but preservation purists (and many design review boards) still prefer the real thing and so do we!
Some SDLs use putty-glazed, permanently adhered lites—but if you’re in a historic district, ask before you install or you may waste a significant investment.
Final Word
True divided lites are more than just a stylistic throwback—they’re a window into how buildings were made, how craftsmen worked, and how light was managed before modern technology.
If your home has TDL windows, you’ve got something special. With proper care—or thoughtful replication—they’ll serve another 100 years, beautifully. At Austin Historical, we preserve, reglaze, and replicate true divided lites every day, with the reverence (and precision) they deserve.
Because when it comes to historic windows, we don’t fake it—we frame it.
