Window Terminology and Anatomy

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    French windows
    12 Mar, 2020, 12:58 AM

    Have you ever wondered what the different parts of your window are called? Well, probably not – most people don’t! However, if you’ve got a damaged or rotten window and you’re getting it repaired, it can definitely help to be able to accurately describe which parts of your window is damaged to your repair person. Window terminology is a little bit tricky, because people tend to substitute words for similar parts of windows into other parts, and over time they’ve just become accepted. Luckily, this handy guide should help clear up a little bit of confusion about what the parts of your window are actually called, so that you can start using window terminology like a pro!

    We’ll start with the traditional window design, that you do see in a lot of classic Victorian and heritage homes. Of course, there are modern versions of this window design that many homes do still have, but they’re definitely less common nowadays with people opting for awning windows with winders and fly screens for ease of use, and for keeping those pesky flies out. These older styled windows are beautiful and ornate, and upkeep on them can be a little bit tricky as they start to age, simply due to how many individual pieces of timber go into each part of the frame, especially on the more stylistic and ornate versions.

    Window terminology and window anatomy for traditional windows
    The anatomy of a traditional window design

    Single Hung and Double Hung
    Yes, we’re still talking about window anatomy here! This refers to the how many movable window assemblies there are. On a single hung setup, the upper sash is fixed in place and cannot be moved. On a double hung setup, both the upper sash and the lower sash are movable.

    Window Sash
    This refers to the window assembly that contains the window panes. On the diagram to the left, we’ve circled each sash with a dotted line. The upper sash is fixed on a single hung window, as described above. The lower sash opens up on both versions. The sash assembly is made up of the glass window panes, rails, stiles and muntins.

    The mechanism which allows you to lock the sash.

    The horizontal members of the sash. The lower rail and upper rail terminology is used to describe the lower-most and upper-most rails on the window assembly. On a double hung window, there’s a rail in the middle of the entire window which overlaps when both sashes are closed. This rail is called the ‘meeting rail’.

    The vertical members of the sash.

    The muntins are rigid bars which separate the glass panes and hold them in place. This is very often mistaken for a mullion, but they’re definitely not the same thing. We’ll show you the difference on the diagram below.

    Window Pane
    The separate panels of glass that form the window.

    Head, Jamb and Sill
    These are the parts which make up the main structure of the frame.
    The head is the top horizontal member of the frame.
    The jambs are the vertical members of the frame.
    The sill is the lower horizontal member of the frame.
    Window stools are very often mistaken for the sil, but it’s an easy mistake to make as the stool hides the sil on many of these older, more ornate window designs.

    This is the moulded, often ornate, housing which hides the elements of the frame (the head, jamb and sil). On many older, high-end Victorian era homes these are custom moulded or machined and cannot be easily replaced if damaged. A custom piece would need to be carved or machined to match the existing design, and this is a specialty thing that would be quite costly.

    The timber brackets which hold the sashes in place.

    The stool is a decorative piece which covers the sill and extends out. This is what you’ll notice a lot of people will put small pot plants or decorations on, and is what gets mistaken for the window sill very frequently.

    The decorative lower lip that is set back from the stool and sits directly under the frame. This is nonexistent on most modern window designs.


    Next, we’ll move on to a more simplistic type of window. This is the sort of window that most Aussie homes have, especially where the window itself is fixed and does not have a winder that allows you to open it (although the anatomy of these is again very very similar). On these windows, there’s less ornamentation and the main frame structure is exposed. They’re also the type of window that we find 90% of the rotten window repairs we have to do are on.

    Window terminology and window anatomy
    The anatomy of a simple window design

    Head, Jamb and Sill
    On this type of window, the components are exposed. The parts are still the same as the above more ornate style of window, but they’re no longer covered by a casing.
    This type of window still has sashes, however these are now fixed in place rather than opening. As with the more ornate window design above, the sash is still contains stiles, muntins and window panes.

    The vertical members of the sash.

    The bars which separate the individual window panes and hold them in place.

    The vertical member which separates the sash assemblies.

    Muntin vs. Mullion
    Now we come to the age old question of the difference between a muntin and a mullion. Most people will just refer to all horizontal window dividers as mullions, however this is actually inaccurate. The mullion is the part which separates the individual assemblies, whereas the muntin is the divider which separates the individual pieces of glass. It’s also the part that the glass is immediately fixed to. Mullions are part of the frame assembly, while muntins are part of the sash. On some windows it’s particularly difficult to differentiate between the two because the glass is sometimes fixed straight to the main frame assembly and doesn’t include a sash at all.

    The head is the highest horizontal member of the frame.

    The transom is the horizontal member of the frame, not including the lowest one.

    The sill is the lowest horizontal member of the frame.

    You will also find that door anatomy and door terminology is very similar – almost identical in fact. The biggest differences being that there’s very rarely glass panes on a door, and the sill is normally referred to as the threshold. We’ll do another one of these informational posts with door anatomy and door terminology to help you out another day!

    Now that you’re armed with all this window terminology and window anatomy, you should be able to accurately identify which parts of your rotten windows or damaged windows need repairs. Contact us today if you’ve got questions, or if you have a window that needs repairs! Remember, providing pictures on our contact form will help us process your enquiry more quickly.

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