Even the best windows will let some water through. It is not uncommon for the sash channels in slider windows to have some sitting water after a rainfall. A great design feature of modern windows is the addition of water drainage channels. No matter how well it is designed, an operable unit will inevitably retain some water after a severe rainfall, or because of extreme condensation. But while bad windows will pool that water and let it leak into the home, drainage channels are designed to move water away from the wall, and prevent leaks in new windows.

When talking about water drainage in modern windows it is important that this water stays between the operable parts of the window without penetrating the sealed unit or frame components. This is especially crucial as temperatures begin to drop. You don’t want any water freezing between the sashes as this may cause sealed unit failure because of vast changes in temperature.

Integrated into most windows, drainage channels allow for water to seep out and away from the frame, preventing pooling that can result in moisture damage.


As with most things related to high-efficiency windows, correct installation is crucial in ensuring the drainage channels are allowed to function properly. If the window is not level an excessive amount of water will pool on one side of the window. Similarly, if a unit is not installed plumb into the opening, with the panes tilting inward or outward, the water may not be allowed to drain away from the frame.

While drainage channels are suitable for all operable units, slider and double slider windows tend to experience the most issues with water drainage channels. This is because their design integrates more grooves for water to collect in.

An extra feature that comes standard with windows that have drainage channels are the exterior drainage flaps. Essentially these flaps act like a one-way door and let the water our without allowing insects to enter your home.


Remember, proper water drainage is essential to longevity and efficiency of your windows. Ensuring that as little water as possible collects in your operable units will prevent damage to your house and save you money in the long term.

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