Sash? Energy Star? Who knew there was a separate dictionary for windows? Regardless of where you are in your process, knowing some basic terms and parts of a window will help you research and decide with confidence.


Let’s get started by tackling the standard parts and components. Not quite there yet? Check out our top 9 reasons to replace your windows.


Apron: This is the piece of casing or decorative trim attached to the wall immediately beneath the sill of a window. Sometimes it is painted to match the window frame, sometimes it is stained or finished wood.


Argon Gas: Argon is a nontoxic, colorless, odorless and tasteless gas injected between glass panes to improve their energy efficiency. It dramatically reduces heat loss when used between panes of glass in a window. Argon is 6 times denser than air and is a key component in affordable, energy efficient windows.


Balance System: A mechanical device that uses springs or weights to hold a window open at the position you set it by counterbalancing the weight of the sash during opening/closing. A block and tackle system in the jamb liner is a sign of a higher quality double hung window.


Casing: Casing is exposed molding or framing around an entire window. Casing on the sides of windows is called side casing and on the top is called head casing. It can be installed on either the inside or outside and covers the space between the window frame or jamb and the wall. Casing is also commonly referred to as trim.


Cladding: Is a durable, exterior covering around a window frame that protect the frame from warping or splintering. Exterior cladding can be metal, fiberglass, or vinyl composite and requires less maintenance. Many window frame types have it but they’re especially common in wood windows -- our selection of Andersen, Pella, and Harvey wood windows all have cladding systems.


Desiccant: This substance is used in insulating glass to prevent windows from fogging up.


Double Hung: A window with two movable/operable sashes which open and close vertically is called a double hung window.


Energy Star®: When you see an Energy Star® logo on a product, you know it conforms to energy-efficiency guidelines as set out by the government environmental agency. All windows and doors installed by Renoviso are Energy Star certified.


Fixed panel: An inoperable panel or sash of a window. As it sounds, it is fixed and does not open.


Frame: The frame houses all of the parts and components of a window. Think of it as the vertical rectangle surrounding your window. It is the stationary portion of a window that encloses either the glass or the sash and consists of the head jamb (top), sill (bottom), and side jambs.


Glazing: This is the process of installing glass into windows. Insulating glass glazing is when two panes of glass are installed separated by a spacer and usually filled with an energy efficient gas fill like Argon.


Grids: These narrow strips that lie across or within a pane of glass. They can often appear in a grid-like pattern. Grids can add or maintain style in your home and can be added in any design you want to virtually any window we offer. For more in-depth information, checkout our How to: Pick Grids for Your Windows.


Grilles: Removable grid-like dividers that are usually rectangular in shape. They can be snapped on or off which allows for easy cleaning. Harvey, Pella, and Andersen all have grille options.


Jamb: Jambs are the vertical or horizontal posts of a window frame. The top part of the window frame is called the head jamb and the sides of the window frame are called side jambs.


Krypton Gas: Krypton is a nontoxic, colorless, odorless and tasteless gas injected between glass panes to improve their energy efficiency. It dramatically reduces heat loss when used between panes of glass in a window. Krypton is 3 times heavier than air and is a component in energy efficient windows. More expensive than Argon.


Interior casing: This is the interior trim around the window.


Lift: A handle or grip installed on the bottom rail of the lower sash of a double-hung window to make it easier to raise or lower the sash.


Mullions: A major structural piece that binds two or more windows. They’re usually vertical but can be horizontal members between adjacent windows that provide structural support and binds window units together.


Operator: This is the arm crank used to open and close hinged windows. Most common in windows above the sink in the kitchen.


Sash: The movable or stationary panel of a window is a sash. It holds the panes of glass together and is a main component of a window along with the window frame. To laypeople and non-pros, this is probably what you think of when someone says the actual word, “window”. The sash consists of the following parts:


  • Check rails:   Horizontal sash members that meet as in double hung units. These could also be vertical check stiles, as in the glider or patio door.
  • Glass:  Glass in energy efficient windows come in double pane or triple pane combinations. Double pane has two and triple pane has, wait for it, three panes. There are many types of glass that can be used in a window including low-emissivity or low-e glass to obscure (for bathrooms) or even tempered (enhanced safety as it shatters into little pieces)
  • Rails:  The horizontal members of the frame of a sash. Where the window “slides into” the frame.
  • Stiles:  The vertical sash members, similar to a muntin.


Sash Lock: The lock on your window that secures the sash to the frame on a casement or awning window, or secures two sashes at the check rail on a tilt or sliding window.


Screen: A close-mesh woven screen material of metal, plastic, or fiberglass attached to aluminum or wood outside the frame. Screens are important to let light and air through but not insects.


Sill: The horizontal piece forming the bottom of a window frame on the outside of the window.


Silicone sealant: A powerful adhesive used in many different applications. It is used in window installations because it’s an excellent insulator and keeps moisture and heat/cold out. It stays flexible at all temperatures, is completely waterproof and bonds well on virtually any surface.


Sloped Sill: A sloped sill is the outside of the window sill and is sloped downward to allow water to run off. A common pitch or slope for a sill is 3’ by 12’ which allows for good rain drainage.


Stool: A horizontal trim piece that laps the window sill above the apron and extends beyond the interior casing.


Stiles: The main vertical part forming the sides of the window frames. They are the vertical supports of the frame of the window sash. Stiles are visible on the sides of windows.


Stop: A molding or insert between the window sash and the jamb.


Hopefully these terms help you feel more comfortable and confident as you continue your research on how to buy windows for your home. Armed with this knowledge you can get an online window quote for your project directly on


Have a question? We’d love to help you.  Direct access to a real person is always a step away: and 617-848-9610.