Parts of a Window
Every part of a window by name — what it does, what goes wrong with it, and how it's repaired.
The Parts of a Window at a Glance
Tap a part's name in the list to see how it's repaired.
- Brick mold / exterior casing — trim framing the window outside. Brick mold repair →
- Head — the top of the window frame. Frame repair →
- Jambs — the sides of the frame; rot starts at their bottoms. Frame & jamb repair →
- Top sash — the upper movable (or fixed) frame holding glass. Sash repair →
- Bottom sash — the lower frame you lift; its bottom rail rots first. Rotted sash →
- Rails & stiles — the horizontal (rails) and vertical (stiles) pieces of a sash.
- Meeting rail & sash lock — where the two sashes meet and lock. Locks & hardware →
- Muntins / grilles — bars that divide the glass into panes, real or decorative.
- Glass unit (IGU) — two panes sealed together; fogging means the seal failed. Foggy glass →
- Exterior sill — the sloped bottom that sheds water; it rots first. Sill repair →
- Stool (interior sill) — the ledge inside the room. Interior sill repair →
- Apron — the trim board under the stool.
- Weatherstripping — the seal between sash and frame. Drafts & leaks →
- Balance (hidden in the jamb) — the spring or cord that holds a sliding sash up. Balance repair →
Every part can be repaired on its own — the window stays.
Parts of the Window Frame
The frame is the fixed box set into the wall. The parts that move or hold glass sit inside it.
Head
The top of the frame. It rarely fails on its own, but water that gets past the trim above it can stain or rot it. Window frame repair →
Jambs
The two sides of the frame. On sliding windows they hold the tracks and hide the balances; on casements they carry the hinges. The bottom ends of the jambs soak up water from the sill and are a common spot for rot. Frame & jamb repair →
Sill (exterior sill)
The sloped bottom of the frame, outside. It sheds rain and snowmelt away from the house — which also makes it the first part of a wood window to rot when its paint fails. Window sill repair →
Stool (interior sill)
The flat ledge inside the room that most people call the window sill. Winter condensation running down the glass can stain and rot it. Interior sill repair →
Apron
The trim board under the stool, inside. It's mostly decorative and usually only needs attention if water has been running behind it.
Brick mold and casing
The trim that frames the window — casing inside, and outside on brick homes a heavier profile called brick mold. Its bottom corners rot where they meet the sill. Brick mold repair →
Mullion
The post between two windows set side by side, as in a bay window or a pair of casements. Water collects on it from both sides, so it can rot from the inside out. Bay window & mullion repair →
Parts of the Sash
The sash is the frame that holds the glass. On most windows it moves; on picture windows the glass sits directly in the frame.
Rails and stiles
The four pieces of a sash: rails across the top and bottom, stiles up the sides. The bottom rail takes the most water and is where sash rot starts; the corner joints between rails and stiles loosen with age. Rotted sash repair →
Meeting rail
On double-hung and single-hung windows, where the top and bottom sashes overlap in the middle. The sash lock sits on it, and gaps here let in drafts. Double-hung window repair →
Muntins and grilles
The bars that divide the glass into smaller panes. On old wood windows they're real muntins holding separate pieces of glass; on most newer windows they're decorative grilles on the surface or sealed between the panes.
Glass unit (IGU)
Most windows from the last few decades have an insulated glass unit: two or three panes bonded around a spacer, often with a coating and gas between them for insulation.
When the edge seal fails, moisture gets in and the glass looks foggy — the fix is a new unit, not a new window. Foggy window repair → · Glass replacement →
Glazing
Whatever holds the glass in the sash. Newer windows use snap-in glazing beads; old wood sashes use glazing putty over small metal glazier's points. Dried, cracked putty lets water into the wood. Window glazing →
Balances, Locks, Cranks & Hinges
The parts that make a window open, stay open and lock — usually the first thing to wear out, and usually the cheapest to fix.
Balances
Springs hidden in the side jambs of double-hung and single-hung windows that carry the sash's weight. When they wear out, the window slams shut or won't stay up. Window balance repair →
Sash cords and weights
The older version of a balance: a rope over a pulley with an iron weight hidden in the wall. Cords fray and snap; the weights almost never need replacing. Sash cord replacement →
Pivot shoes and tilt latches
Small parts on tilt-in double-hungs: the tilt latches at the top of the sash let it tip in for cleaning, and the pivot shoes at the bottom connect it to the balances. Both are plastic and crack with age. Window hardware repair →
Sash lock
The latch on the meeting rail that locks a double-hung and pulls the sashes tight together. Window lock repair →
Crank operator and hinges
On casement and awning windows, the operator is the gear box you turn with the crank handle; the hinges are the arms and tracks at the top and bottom of the sash. Stripped operators and worn hinges are the usual reasons a casement won't open or close tight. Casement & awning window repair →
Rollers
Small wheels under the sash of sliding windows and patio doors. When they wear flat, the panel drags in its track. Sliding door repair →
The Seals That Keep Air and Water Out
Weatherstripping
The flexible seal between the sash and the frame — foam, felt, pile or rubber. When it flattens or falls out, the window leaks air even though it looks fine. Drafts & leaks →
Exterior caulk
The sealant between the window's outside trim and the wall. Cracked caulk lets rain run behind the trim and into the frame. Leaking window repair →
The glass unit's edge seal
The seal around the edge of a double-pane unit, covered above. It isn't repairable on its own — a failed seal means a new glass unit.
Screens and Storm Windows
Screen
A mesh panel in a light aluminum frame, held in with springs or clips. Torn mesh is rescreened; bent or missing screens are made to fit. Window screen repair →
Storm window
A second window added outside (or inside) an older window for insulation, usually with sliding glass and screen panels in an aluminum or wood frame. Storm window repair →
The Difference That Matters for Repair
Frame vs. sash is the distinction that decides most repairs. The frame is built into the house; the sash is the part that holds the glass.
When a sash fails — rot, broken glass, loose corners — it can be repaired, or a new sash made to fit the existing frame. When the frame fails, the rotted section is rebuilt in place.
Either way, the window stays in the wall, the interior trim and drywall stay untouched, and the cost is a fraction of a new window. Not sure which part is failing? Send a photo — or start with the window triage guide.
Not Sure Which Part Is Broken?
Send a photo of the window. We'll tell you which part has failed and what it costs to fix.
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