Fah lai is the name for a traditional northern-style sliding window lattice. The system consists of a series of vertical wooden planks across the window.

This can be closed off by a similar set of overlapping planks in a movable frame, allowing for the window to be shut by sliding the frame in front of the openings.

It is typically found on traditional wooden houses that are in general referred to as Reuan Thai (fig.), especially those built in northern Thailand, due to the cooler climate.