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  • Writer's pictureOakmont Glazing Systems Ltd

Glazing bars, mullions and transoms - what is the difference?

We know terminology in the glazing world can sometimes take time to get used to and understand, so in this blog we want to explain the differences between glazing bars, transoms and mullions so you know exactly what you’re ordering.

Let’s start with glazing bars. What is a glazing bar? A glazing bar is a slim piece of timber or aluminium that is stuck to the inside and outside of the glass on a window or door to create a design of your choosing. Glazing bars can be used both vertically and horizontally and are typically used to create that steel look, especially in aluminium. Glazing bars create the look of individual pieces of glass within your window or door without having to have all individual pieces of glass, which makes them the most cost-effective way of adding more character and creating a particular look. Glazing bars come in different styles with some being square and simple and some being more decorative, it all depends on your preference.

Now onto transoms. Transoms are the horizontal lines in windows and doors, but rather than being on the inside and outside of the glass like glazing bars are, transoms actually split the glass into two and are chunkier than glazing bars. Transoms are used when you have an opening window above a fixed window to create the separate sashes or vice versa. They are also used when you have a tall window. Sometimes, especially when using a timber or aluclad window, the height of your window may be too tall to be made as one, so we use a transom to split the glass into two. Transoms come in all materials for glazing such as UPVC, timber, aluclad and aluminium.

Now onto mullions. Mullions share the same concept as a transom, they split the glass into two, but instead of doing this horizontally, mullions do this vertically. If you have an opening window next to a fixed window, or a fixed window next to a fixed window, the vertical part that separates the two is the mullion. Mullions are made in all materials for glazing such as UPVC, timber, aluclad and aluminium.

In summary, glazing bars are slimmer than transoms and mullions and are used for decorative purposes to add more character or create a particular style to your glazing. Transoms and mullions are used where they are needed, either to separate two sashes or to split the glazing up if a window is too big to be made in one.

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