What are the parts of a window?
What are the parts of a window?
A window is made up of dozens of individual components that work together to provide light, ventilation, insulation, and security. Understanding these parts helps homeowners diagnose problems, order the right replacement pieces, and communicate effectively with contractors. Whether you're repairing a broken sash lock or replacing a worn-out balance spring, knowing the correct terminology saves time and money.
Every window, regardless of style, shares a common set of structural and functional parts. These include the frame, sash, glass pane, hardware, weatherstripping, and various seals. The specific components vary depending on whether you have a double-hung, casement, awning, or sliding window.
| Window Part Category | Key Components | Primary Function |
|---|---|---|
| Frame | Head, sill, jambs, jamb liners | Structural support |
| Sash | Rails, stiles, check rail | Holds glass, opens and closes |
| Glass | Panes, glazing beads, spacers, gas fill | Light transmission, insulation |
| Hardware | Locks, handles, operators, hinges | Operation and security |
| Balances | Spiral, block and tackle, channel | Counterweight for sash movement |
| Weatherstripping | Pile, foam, bulb seals | Air and water sealing |
| Screens | Insect screens, retractable screens | Ventilation with pest protection |
Frame and structural parts
The frame is the backbone of any window. It anchors the entire assembly into the wall opening and supports every moving and stationary component. A window frame consists of four main pieces that form a rectangular border around the glass and sash.
| Frame Component | Description |
|---|---|
| Head (head jamb) | The horizontal piece at the top of the window frame |
| Sill | The horizontal piece at the bottom, angled to shed water |
| Side jambs | The two vertical pieces on either side of the frame |
| Jamb liners | Interior tracks that guide the sash up and down |
| Sill cover | Protective cap placed over the sill to prevent water damage |
| Casing (trim) | Decorative molding around the interior and exterior of the frame |
| Stool | The interior horizontal shelf at the bottom (often called the windowsill) |
| Apron | Trim piece beneath the stool |
Head and sill
The head is the topmost horizontal member of the frame. It bears structural load from above and provides a stop for the upper sash. The sill sits at the bottom and is slightly sloped outward to direct rainwater away from the interior. In older homes, wooden sills are prone to rot and may need sill covers for protection.
Jambs and jamb liners
Side jambs run vertically on each side of the window and form the tracks in which the sash slides. Modern double-hung windows use jamb liners, which are removable vinyl or aluminum channels installed inside the jambs. These liners house the sash balances and allow the sash to tilt inward for cleaning.
Jamb liners are one of the most frequently replaced window parts. When they crack or warp, the sash becomes difficult to operate or won't stay in place. Andersen, Pella, and other major manufacturers sell brand-specific jamb liners that must match your window series and year of manufacture.
Sash components
The sash is the movable (or fixed) panel that holds the glass. It consists of horizontal rails at the top and bottom and vertical stiles on each side. In a double-hung window, the meeting point where the upper and lower sash overlap is called the check rail.
Replacement sashes are available as complete units from most window manufacturers. This is often a more practical solution than replacing individual sash components, especially when the wood is damaged or the glass seal has failed.
Glass and glazing components
The glass unit is the most visible part of any window and the primary barrier between your home's interior and the outside environment. Modern windows use insulated glass units (IGUs) rather than single panes, providing significantly better energy efficiency.
| Glass Component | Description |
|---|---|
| Glass pane | The sheet of glass itself; may be tempered, laminated, or annealed |
| Insulated glass unit (IGU) | Two or three panes sealed together with gas fill between them |
| Spacer | Material between panes that maintains consistent spacing and reduces heat transfer |
| Gas fill | Argon or krypton gas between panes for improved insulation |
| Glazing beads | Strips that hold the glass pane securely within the sash frame |
| Glazing compound (putty) | Sealant used on older windows to hold glass in place |
| Low-E coating | Microscopically thin metallic layer that reflects heat |
| Grilles (muntins/grids) | Decorative bars that divide the glass into smaller sections |
Grilles and muntins
Grilles, sometimes called muntins or grids, create the appearance of multiple smaller panes within a single glass unit. Traditional windows used true divided lites, where each small pane was individually glazed. Today, most grilles are decorative and come in three styles:
- Interior wood grilles: Snap-in grilles placed on the interior side of the glass for easy removal and cleaning
- Grilles between the glass (GBG): Permanently sealed between the two panes of an IGU
- Simulated divided lites (SDL): Grilles applied to both the interior and exterior glass surfaces with a spacer bar between panes
Glazing beads
Glazing beads are the narrow strips, typically vinyl or wood, that hold the glass pane into the sash frame. On modern windows, they snap into place and can be pried out when the glass needs replacement. On older wood windows, glazing compound (putty) serves the same purpose and must be carefully chipped away and reapplied during reglazing.
Window hardware
Hardware refers to the mechanical components that allow you to open, close, lock, and secure a window. The specific hardware depends on the window type. Double-hung windows use locks and lifts, while casement windows rely on crank operators and multi-point locking handles.
| Hardware Type | Used On | Typical Cost Per Unit |
|---|---|---|
| Sash locks and keepers | Double-hung, single-hung | $5 - $20 |
| Sash lifts and handles | Double-hung, single-hung | $3 - $15 |
| Casement operators (cranks) | Casement, awning | $8 - $60 |
| Casement locking handles | Casement | $10 - $35 |
| Awning operators | Awning | $10 - $110 |
| Sliding window handles and locks | Horizontal slider | $5 - $25 |
| Window safety devices | All types | $5 - $30 |
| Tilt latches | Double-hung (tilt-wash) | $4 - $12 |
Sash locks and keepers
The sash lock (also called a cam lock or crescent lock) sits on the check rail of the upper sash, while the keeper mounts on the lower sash's check rail. When engaged, the lock draws the two sashes tightly together, improving both security and the air seal. These are among the most commonly replaced window parts because they endure frequent use and can wear out or break over time.
Operators and cranks
Casement and awning windows use a crank-style operator to push the sash open. The operator is a geared mechanism attached to an arm or track that swings the sash outward. When an operator fails, the window may become stuck open or closed. Replacement operators range from about $8 for basic models to over $100 for specialty awning operators.
When ordering a replacement operator, you'll need to know the arm length, body style (square, teardrop, or round), mounting position (face mount or sill mount), and handing (left or right).
Handles, lifts, and covers
Sash lifts are the small handles or finger pulls on double-hung windows that help you raise the lower sash. They come in several styles, including bar lifts, ring pulls, and flush-mount finger pulls. Casement windows use lever-style handles with cover plates (bezels) and escutcheon plates for a clean finished look.
Sash hinges
Casement and awning windows use hinges to pivot the sash open. These hinges are typically made of stainless steel and come in specific sizes matched to the window dimensions. Over time, hinge shoes and pivot bars can wear out, causing the sash to sag or become difficult to close properly.
Window balances
Sash balances are the spring mechanisms inside double-hung and single-hung windows that counterbalance the weight of the sash. They allow the sash to stay open at any position without slamming shut. When a balance fails, the window slides down on its own or becomes very difficult to raise.
| Balance Type | Description | Typical Cost |
|---|---|---|
| Spiral (tube) balance | Coiled spring inside a metal tube; available in tilt and non-tilt versions | $6 - $21 |
| Channel balance | Spring-loaded mechanism housed in a metal channel | $10 - $15 |
| Block and tackle balance | String-and-pulley system with a coiled spring inside a compact housing | $11 - $12 |
| Constant force balance | Coiled steel spring that provides uniform tension throughout travel | $15 - $35 |
| Caldwell Ultra-Lift balance | Premium coil balance system for heavier sashes | $30 - $60 |
| Sash weights (historic) | Cast iron or lead weights on ropes inside the wall cavity | $10 - $30 |
Spiral balances
Spiral balances are the most common type found in modern vinyl and aluminum windows. They consist of a twisted metal rod inside a tube with a spring mechanism. These balances are identified by their length, diameter (typically 3/8" or 9/16"), and tip color. The colored tip (red, white, blue, green, yellow, or black) indicates the spring tension rating, which must match the weight of your sash.
Spiral balances come in tilt and non-tilt versions. Tilt balances have a special shoe at the bottom that allows the sash to tilt inward for cleaning. Non-tilt versions hold the sash in a fixed vertical plane.
Block and tackle balances
Block and tackle balances use a pulley system with a nylon cord and a coiled spring. They're common in wood and clad-wood windows. The entire mechanism is contained in a small housing that clips into the jamb liner. These balances are durable and provide smooth operation, but they're more expensive to replace than spiral types.
Weatherstripping and seals
Weatherstripping fills the gaps between the sash and frame to prevent air infiltration, water intrusion, and dust entry. Over time, weatherstripping compresses, cracks, or falls out entirely, leading to drafts and higher energy bills. Replacing worn weatherstripping is one of the most cost-effective window repairs you can make.
| Weatherstripping Type | Common Location | Material |
|---|---|---|
| Pile (fin seal) | Sash channels, sliding windows | Polypropylene fibers on a plastic strip |
| Bulb seal | Sash perimeter, casement windows | Flexible vinyl or silicone |
| Foam tape | Fixed sash stops, frame perimeter | Closed-cell foam with adhesive backing |
| V-strip (tension seal) | Sash channels on wood windows | Vinyl or bronze |
| Interlocking metal | Meeting rails on historic windows | Bronze or aluminum |
| Panel gasket | Patio door panels | EPDM rubber or silicone |
| Door sweeps | Bottom of storm doors | Vinyl, rubber, or brush |
Weatherstripping is typically sold in linear feet or as pre-cut kits designed for specific window models. Brand-specific weatherstripping from Andersen, Pella, or Marvin ensures a precise fit, while generic products from hardware stores can work for standard-sized openings.
Insect screens and screen parts
Insect screens allow fresh air in while keeping bugs out. Nearly every operable window style has a corresponding screen type. Screens can be full, half, or retractable depending on the window design and homeowner preference.
| Screen Type | Window Style | Key Components |
|---|---|---|
| Half screens | Double-hung | Frame, mesh, spring clips or pull tabs |
| Full screens | Double-hung, single-hung | Frame, mesh, corner connectors |
| Casement screens | Casement, awning | Frame, mesh, plunger pins or turn clips |
| Gliding insect screens | Sliding windows, patio doors | Frame, mesh, rollers, pull handles |
| Retractable screens | Various | Housing, mesh roll, tracks, handles, latch receivers, damper endcaps |
Screen mesh is available in fiberglass (most common), aluminum, stainless steel, and specialty pet-resistant materials. When the screen fabric tears but the frame is intact, you can rescreen it using a spline roller and new spline cord for just a few dollars.
Retractable screen parts
Retractable screens roll into a compact housing when not in use. Their individual components include screen and latch housings, handles and latch receivers, replacement glides, damper endcaps, screen tracks, sill adapters, and screw packs. These parts are specific to the screen manufacturer and model.
Parts by window type
Different window styles use different combinations of parts. Here's a breakdown of the unique components associated with each major window type.
| Window Type | Unique Parts |
|---|---|
| Double-hung | Sash balances, jamb liners, tilt latches, sash locks, sash lifts, check rail |
| Single-hung | Sash balances, stationary upper sash, glazing beads, sash locks, sash lifts |
| Casement | Crank operators, sash hinges, multi-point locks, handles, covers, bezels |
| Awning | Roto gear operators, sash hinges, locking handles, electric openers |
| Sliding (gliding) | Window rollers, track, sash guides, window handles, window locks |
| Patio door (gliding) | Door rollers, thumb latches, auxiliary security locks, exterior keyed locks, gliding handles, cover plates |
| Patio door (hinged) | Door hinges, lever handles, lock mechanisms, strike plate extenders, escutcheon plates, handle extenders, door stops |
Double-hung window parts
Double-hung windows have two operable sashes that slide vertically within the frame. Both sashes require their own set of balances, and the meeting point between them needs a sash lock and keeper. Modern tilt-wash versions (produced from the early 1990s onward) include tilt latches that release the sash for inward tilting, making it simple to clean the exterior glass from inside the home.
Casement window parts
Casement windows swing outward on hinges and are operated by a crank mechanism. The operator is the part that most commonly fails. Replacement operators must match the original in arm length, body type, and handing (left or right). Casement windows also use multi-point locking systems with a single handle that engages locking points at the top and bottom of the sash simultaneously.
Patio door parts
Patio doors share many components with windows but also include door-specific hardware. Gliding patio doors use rollers mounted on the bottom of the door panel to travel along a track. These rollers wear out over time and cause the door to drag or stick. Hinged (French-style) patio doors require heavy-duty hinges, multi-point lock mechanisms, and lever handles.
Common patio door parts include screen door hardware, auxiliary security locks, exterior keyed locks, and interior thumb latches. Cover plates and escutcheon plates provide a finished appearance around handles and locks.
Common window parts costs
Most window parts are relatively affordable, making DIY repair a cost-effective alternative to full window replacement. Prices vary based on the manufacturer, window series, and whether you're buying generic or brand-specific parts.
| Part | Typical Cost Range |
|---|---|
| Spiral tilt balance (3/8") | $6 - $12 |
| Spiral tilt balance (9/16") | $8 - $21 |
| Channel balance (9/16") | $10 - $15 |
| Block and tackle balance | $11 - $12 |
| Caldwell Ultra-Lift balance | $30 - $60 |
| Casement operator (crank) | $8 - $57 |
| Awning operator | $10 - $110 |
| Casement locking handle | $10 - $32 |
| Tilt latch set | $4 - $12 |
| Sliding window roller | $3 - $5 |
| Sash lock and keeper | $5 - $15 |
| Balance tension tool | $20 |
| Patio door handle | $80 - $100 |
| Locking handle (single-point) | $6 - $9 |
How to identify the right window parts
Ordering the correct replacement part requires identifying your window's manufacturer, product series, and approximate year of manufacture. This information is usually found on a label located on the window frame, visible when the sash is open or tilted inward.
Find your manufacturer and series
Look for an identification label on the top of the window frame, the side jamb, or the spacer bar between panes of glass. The label typically includes the manufacturer's name, product line, and a date code. For Andersen windows, the series number (100, 200, 400, or A-Series) and production era are critical for ordering compatible parts.
Take accurate measurements
Many parts are size-specific. For balances, measure the tube length and diameter. For operators, measure the arm length and note the body shape. For insect screens, measure the width and height of the screen opening. Taking photos of the existing part, including any stamps or markings, can also help suppliers match you with the right replacement. Knowing standard window sizes can also be helpful when ordering replacement components or screens.
Where to buy window parts
Window parts are available from several sources:
- Manufacturer direct: Companies like Andersen sell parts through their own catalogs and websites, ensuring exact compatibility.
- Specialty retailers: Sites like WindowParts.com, SWISCO.com, and WindowRepairParts.us carry parts for dozens of brands.
- Hardware suppliers: Prime-Line and other distributors sell universal and brand-compatible hardware through home improvement stores.
- Local glass shops: Many independent glass and window dealers stock common parts or can order specialty items.
Frequently asked questions
How do I know if my window balance is broken?
If your window slides down on its own when you try to leave it open, or if it's very difficult to push up, the balance has likely failed. You may also hear a snapping sound when the spring breaks. Remove the sash and inspect the balance for visible damage such as a disconnected cord, broken spring, or cracked tube.
Are window parts universal?
Some window parts, like basic sash locks, weatherstripping, and screen hardware, come in universal or standard sizes. However, balances, operators, jamb liners, and replacement sashes are almost always specific to the manufacturer, product line, and production year. Using the wrong part can result in poor fit, operational issues, or damage to the window.
How do I replace a casement window operator?
Start by cranking the window closed. Remove the operator arm from the sash track by sliding it to the release notch. Unscrew the operator from the frame and disconnect any remaining linkages. Install the new operator in reverse order, ensuring the arm length, body style, and handing match the original.
How often should weatherstripping be replaced?
Weatherstripping typically lasts 5 to 10 years depending on sun exposure, moisture, and how frequently the window is operated. Check for drafts around closed windows, visible gaps, or compressed and cracked material. Replacing weatherstripping costs only a few dollars per window and can noticeably reduce energy bills.
What if I can't find parts for my window?
Specialty window parts retailers carry components for discontinued and hard-to-find windows. If you can't identify the part yourself, send photos and measurements to a supplier like SWISCO or WindowParts.com. They often have staff who can match even obscure or vintage hardware. For very old windows, a local glass shop or window restoration specialist may be able to fabricate custom parts.