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Decoding Window Replacement Terms

What the technical jargon in the window and door replacement process really means, and why you should understand it.


When embarking on a window replacement project, sometimes it seems as though window companies or replacement contractors are simply speaking a different language. You’re asked to weigh in on what kind of divided lites you want, whether you need egress, and what color weather strip you might want. Your contractor might propose a sash limiter if you have young kids, or a faux check rail to simulate the look of a double hung window.

Meanwhile, you might as well be in a foreign country because none of these terms make sense, and you’ve been lost since you read the words “simulated divided lite with spacer bar.”

The first step to feeling empowered during the window replacement process is understanding the terminology, and we’re here to help break down the complicated window replacement terms and industry jargon so you can be on a level playing field. We’ve compiled a primer on some of the most uttered phrases during a window replacement project—replacing complicated terminology with simple explanations—so you can understand the value of certain options, and know what questions you should ask from the get-go.




Sash = what holds the glass in the window
This is the part of a window that comes in contact with the glass and holds it in place. When you push a window up or out to open it, you’re moving the sash. The part that runs up and down each side is the stile, and the part that runs across the top or bottom is the rail. In your replacement conversations, a professional might bring up narrow stiles and rails as a selling point—for example, less width means more room for the glass and more daylight.


Sash Limiter or Window Opening Control Device = safety device
If you have small children or if your local code requires it, a sash limiter or window opening control device may be necessary on upper floors for restricting how far a window can open. A sash limiter means that your sash can only open about four inches, helping to prevent falls through open windows. A window opening control device achieves the same goal, but has a two-step release process that allows the sash to open fully if you need it to—for example, if you need that window to be an exit point. Check with your window professional on local requirements and what your options are to meet these safety standards.


Frame = structure to put the sash in
Without the frame, your window sashes would have nothing to fit into—no way to attach to the wall and no framework to actually operate. The frame provides structure and support. The bottom of the frame is called a sill, the top is a header and the sides are called jambs. When you replace, there are various options that allow you to put a “frame within a frame” rather than stripping down to the studs. We agree, it’s a bit confusing, so we wrote a separate blog post on insert vs. full-frame window replacement.

*Pro tip: the frame is not to be confused with your window trim, which is placed on your wall to cover gaps and add decorative flair, and can always be changed later on. The color and material of the frame and sash? Not as easy to change.


Sill = the bottom part of the window frame
Also known as where you might put a few plants, if your sill is deep enough. But, watch out for too many plants near windows, because they can lead to excess condensation.


Muntins/Simulated Divided Lites = the things that make a grid pattern
These decorative bars are attached to glass to create the look of a grid. You can have just a couple, or many, to simulate the look of lots of individual glass panes, like the old days—hence the “simulated” part. The real thing would be called a “true divided lite.” You might also hear these called grilles or muntins by a professional. Your neighbor might refer to “criss-cross lines” in a window or a “window with squares.” Some will actually be in between two panes of glass instead of on the outside, which is referred to as grilles between the glass—or GBG for short—and makes for easy cleaning with nothing attached to the outside of the glass.

*Pro tip: GBG are not to be confused for spacer bars. If you have GBG, you have nothing on the outward-facing part of your window pane. If you were to touch the window, you feel only smooth glass. Spacer bars are also in between your window panes, but they are paired with simulated divided lites on the outside and help give the appearance of separate panes of glass.


Checkrail = the middle part of a double hung window
When you have a double hung window—the kind with two overlapping sashes that can slide up from the bottom or down from the top—the checkrail is where the two parts meet. This is where you’ll see your sash lock, or locking hardware on this type of window.

*Pro tip: An extra-thick muntin/divided lite can be added to other kinds of windows to mimic the classic look of a double hung while offering a different type of window operation. We call this a “simulated checkrail.”


Egress = a point of exit
An egress window is one that’s large enough—as defined by the codes in your area—to count as an entry or exit in case of emergency. Most people think that egress requirements are only for basement bedrooms, but actually all bedroom windows need to meet egress code, and the type or size of the window you’re replacing may not meet current codes. Are yours in compliance? Ask your window expert to help you understand the requirements in your area.


Weather Strip = seal against water and air
Weather stripping—a material that can look like foam or rubber—is a strip of resilient material that seals the tiny space between the sash and the frame to stop air from escaping and water from entering your house. Ask about what color strips are available to best match your window finish color.


Operable Window = window that can be opened or closed
This may seem obvious, but it’s not always clear that there are windows that open and close, and those that don’t. A window that’s higher up or potentially a small window above a larger window or door doesn’t need to open, and is therefore called a picture/stationary window. These can vary in type, including ones that have a sash like an operable window, and ones that just have glass in a frame. For a download on all available window types—including various picture/stationary windows—visit our blog post on navigating window replacement options.


Wash Mode = an ingenious invention for cleaning windows
This is one you didn’t know you needed, but won’t want to live without. It’s a Marvin-exclusive design feature that lets you pivot our Ultimate Casement windows to easily clean the outside of the window while standing comfortably inside your home. A similar Tilt Wash Mode also exists for our Ultimate Double Hung G2 windows. When you’re evaluating window options, ask about how to clean them—especially if you have a two-story home and aren’t into climbing ladders.


Clad = covered
Window and door parts—typically wood—are “clad” when they are covered with a more weather-resistant exterior-facing material. This is often aluminum or fiberglass. Understand the difference between these materials and what it means for the longevity and maintenance of your new windows.




Door Panel = the part of the door that holds the glass and opens/closes
The door panel is like a sash for a window—it’s the part that moves and holds the glass in. Hingesattach the door panel to your door frame, and you’ve got stiles (vertical) and rails (horizontal), just like a window.

*Pro tip: Not all door panels are operable. To create the look of a larger door or a glass wall, a panel that does not open can be added to either side of a sliding or swinging patio door to let more light in.


Door Frame = the part that attaches to the wall
Without a frame, your door panel would have nothing to grab onto. The frame surrounds and supports your door and is what connects to your wall. Just like windows, it’s important to understand your various material options.


Sill = where your door meets the floor
The sill of a door is a bit different from a window—it will be installed in your existing floor. When the door is closed, the weatherstrip sits against the sill, and the two in tandem provide important weather protection. Ask about what your door sill will be made out of, what colors you have to choose from, and if there is a high-performance (for certain climates) or low-profile (sits flush to prevent tripping hazards) option.


Multi-Point Locking System = locks at more places than just the handle
For extra-added security, a door can have locking points above and below the handle and main locking mechanism—extending into the header at the top and sill at the bottom—ensuring that the door is secure from top to bottom by dividing any effort of forced entry across the full length of the door panel, instead of only in the middle. A multi-point locking system can also help keep your door’s seal secure, adding to performance against bad weather.


French Door = Not just a swinging door style
When you picture a French door you might imagine a European-style double door swinging inwards to reveal a beautiful garden outside. That might be true, but French doors aren’t always swinging. The difference between a French door and a patio door isn’t in the way it operates—it’s actually in the width of the stiles and rails on the door panel itself. The vertical stile on a French door will be wider, and the rails at the top and bottom are taller, giving a more traditional appearance. Patio doors have slimmer profiles and a more contemporary look and can swing or slide just like a French door.




Glazing = a fancy word for glass
Glazing generally means the glass panes that go in your window or door, and often includes other items related to the glass panes, like a coating on the surface of the glass, an insulating gas for better energy efficiency and glass sealants.


Low E = a coating to make your windows more energy efficient
Low E, or low-emissivity coating is a thin coating that’s invisible to the eye. It allows light to come through, but not the UV rays that cause your home to heat up from the sun. These coatings are rated from Low E1 (for the Northern United States) all the way up to Low E3, which is recommended to meet climate and code requirements in far South states.


U-Factor = how much heat is lost from your home
Simply put, U-factor measures how well a window keeps heat inside your home. A low number is better, because it means that less heat is traveling from your home to the outdoors through your window or door. This rating is most important in Northern areas, where ENERGY STAR® recommends windows with a U-factor of .25 to .30. In areas where temperatures can be either hot or cold, the recommended factor is closer to the .30 range, and in primarily hot areas, a factor of .40 may be acceptable.

*Pro tip: You might be familiar with R-Value terminology from doing other projects that involve insulation. When you’re evaluating a window or door, R-Value isn’t as “valuable” because it only measures the conductivity of the glass pane. U-Factor is the number you should care about, as it measures heat gain or loss for the entire window or door—including the sash and frame.


Solar Heat Gain = how much heat enters your home
If U-factor tells you how much heat leaves your home, the Solar Heat Gain Coefficient (SHGC) measures how much heat will transfer into your home from the sun. This number can range from zero to one, and the lower the number, the less heat a window or door lets in. Appropriate numbers for your home vary depending on your climate, your home’s orientation, how much shading you have and other factors. For those in cold climates, higher heat transfer into the home (a larger number for SHGC) is often viewed as a positive.


Triple Glazing or Tripane = three panes of glass with insulating air
Triple pane (tripane) glazing provides three panes of glass with Low E coatings—and insulating gas between the panes—and is often marketed as providing better energy efficiency.

*Pro tip: What many don’t know is that triple pane glass doesn’t necessarily mean a window is more energy efficient. Glass coatings, the type of gas used in the spaces between the panes, the design of the window, materials used and installation all play a role. A poorly designed or installed window, or one made with less energy efficient materials overall, may make triple pane glazing an ineffective way to spend your budget.


ENERGY STAR = grades for efficiency
ENERGY STAR is a government program that ‘grades’ the efficiency of replacement windows. You should always check for products that are ENERGY STAR rated, and you can learn how to read an ENERGY STAR label here. Though programs are always changing, be sure to ask your window professional if your energy efficient replacement windows may qualify you for tax credits.


Window/Door Sensor = a solution to “did I lock that window?”
As more and more home solutions become automated, so do windows and doors. There are many sensor options that can tell you whether your windows and doors are locked or unlocked, but they’re often large and bulky pieces that are added to your windows and doors after they are installed. Some manufacturers now offer a hidden solution, and ours is compatible with many common security systems on the market. Find out what options are available to you to prevent unsightly additions to your beautiful new replacement products.

The replacement process can be tricky to navigate, but a better understanding of confusing window or door replacement terminology can help you move forward with confidence.