What is a Window Jamb?

Mary McMahon
Mary McMahon

A window jamb is part of the structural support of a window. Jambs are located inside the framing of the window, along the top and sides, and in the case of windows which open, jambs can house tracks or rails used to manipulate the window, along with devices such as latches which are used to lock the window when it is closed. Similar structural supports around a door are also known as “jambs,” and a “jamb” more generally is any type of vertical support around an opening.

Window jambs are common to many window installations.
Window jambs are common to many window installations.

Technically, window jambs are known as side jambs when they are along the sides of the window, and as head jambs when they run along the top of the window. Jambs are not necessarily required, but they are common to many window installations. Numerous companies which produce windows also make matching jambs and jamb extensions which can be used to help their products fit more snugly; the jamb can be a weak point in a window if it is not installed properly, allowing for leaks or security concerns.

Jambs are located inside the framing of the window, along the top and sides.
Jambs are located inside the framing of the window, along the top and sides.

The material used to make a window jamb can vary, and may be wood, plastic, vinyl, or metal. Window jambs may be painted to match the trim on a structure, or left unfinished, depending on the material and the aesthetics of the structure. In cases where windows start to move unevenly or gaps appear around the window, replacing the window jamb can sometimes resolve the problem, with less cost than replacing an entire window or reframing the whole window.

A contractor can determine whether or not a window jamb needs to be replaced and do the work relatively quickly. People who are handy with basic construction tasks can also do work on their own window jambs, ranging from fitting new ones to allow a new window to fit into an existing opening to replacing old jambs which are starting to warp, rot, or leak so that an original window can be left in place. It is important to take time when working with window jambs, as a failure to fit them snugly and properly can result in problems ranging from a window which will not open to a window which is so loose that it is easy to pop out of the frame.

People inspecting structures they are thinking about purchasing should also take time to examine the window jambs. If windows are leaky, the jambs will betray signs in the form of staining and rot. In addition to indicating that the jambs need to be replaced, rotting and staining around a window jamb could suggest that there may be other water damage which is not visible, such as rot as the result of water seeping into the structural framing.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


When installing a basement window, how do I get the jamb right? I've been trying to install a replacement basement window, and I can't for the life of my get the jamb to look right.

Does anybody out there have any good basement window installing tips?



How exactly can I clean a window jamb? I have window jamb liners, but they always seem to get so dusty and gross, so how can I clean these out? Is there a way that I can actually keep these clean, or do I just have to keep trying to clean them whenever they get dirty?

Is there some kind of window protection to install on a jamb to keep it from getting dirty?

It's an aluminum window jamb, by the way.


When choosing a window jamb replacement, how do I know what size to buy? All I can find is information on replacement window sizes, I can't find any advice specifically on jambs. Does anybody have any tips about getting the right kind of replacement window jambs?

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