This system is used at places where space is a constraint. They can be used at places where the opening size of the window is not very big. These will have 2 tracks of sliding.
These windows are designed in such a way that they are airtight & water tight. Therefore ensuring that no water comes inside when the windows are closed in case water comes inside when the window is open a provision for water drainage is given such that the water is drained out.
These windows are duly reinforced with thick specially designed Steel for greater strength & Safety of the uPVC window.