What’s a Check Rail?

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Control rails are where glazing frames meet in a window. They consist of two parts and are important for weather sealing and safety. Concealed locks and weather strips can be used for aesthetic purposes and to seal gaps.

Control rails are the portions of windows where the glazing frames meet. Typically, this is in the center of the window. On a two-leaf or single-leaf window, it consists of two parts: the bottom rail of the upper glass frame and the upper rail of the lower glass frame. On a sliding window, it’s where the frames of the vertical panes of glass meet. Usually the window block is placed on the control rail.

A window consists of several parts. The sash is the frame that holds the glass in place. The vertical pieces of the frame are called the uprights and the rails are the horizontal sections.
In double casement windows, the control rail is on the rails that meet in the middle and is known as the meeting rail. On a sliding window, builders sometimes refer to it as the meeting style because it consists of the vertical frame pieces meeting in the center of the window. Other builders often use the term closing rail for both types of windows. People often refer to the individual parts as the upper sash retaining rail and the lower sash retaining rail.

Typically, padlocks on control rails seamlessly join the two rails. This is important for weather sealing and safety. Often when there is a gap, it can cause a loss of energy. This usually allows heated air to escape in cold weather and cooled air in warmer weather. An empty space can also provide a place for insects to enter the building.

In a single sash window, only the upper or lower sash is movable. Where the two doors meet, it is still called a control rail. In some windows that don’t open, the manufacturer will create the appearance of control rails for purely aesthetic purposes, but sometimes people don’t want this grid added because it can impair vision.

For people who don’t like seeing the locking mechanism, a concealed lock may be the answer. This special lock is mounted inside recesses in the control guides. Most of these locks have a visible handle, but this is not as intrusive as seeing the full lock mechanism. Typically, this type of lock requires professional installation because the mating parts must fit together perfectly to ensure an airtight seal. Another consideration when purchasing this type of lock is the control rail clearance, which is the gap between the two panes as the frames slide over each other.

Many companies make special weather strips called weather strips for control rails. Seal the gap that can occur between the two doors. Some window manufacturers mill a cut, groove, or notch, into the rails and sell gaskets for it. In general, the newest style of this paint stripping is bulbous. This replaces the older, less efficient felt style.

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