06/01/26

PVC Windows with movable mullion: When You Need Them

PVC windows with movable mullion are   double leaf structures in which one sash is attached to the other using  special profile. Unlike conventional windows with mullion (a vertical partition in the middle), movable mullion is not rigidly fixed in the frame: it is attached to one of the sashes and moves with it when opened. As a result, when both sashes are fully opened, the opening remains completely unobstructed — there is no central partition.
How does it work in practice? The active sash can be opened for ventilation or fully swung  open. The passive sash is secured by movable mullion  and can only be opened after the active one; typically, it does not have a tilt mechanism. For reliable fastening, special hardware is used: latches, mechanical rods, pneumatic closers, and microlifts.
The main advantage of such windows is the maximally wide light opening. The absence of a mullion increases the glazed area, improves room illumination, and creates a panoramic view effect. This is especially convenient when you need to bring large furniture or appliances into the room. Moreover, the tight fit of the sashes ensures good airtightness: the window reliably protects against noise, dust, and drafts. From an aesthetic standpoint, movable mullion windows look lighter and more modern than those with a partition — they fit well into complex architectural shapes, including polygonal and circular openings.
There are also some considerations. The width of each sash usually does not exceed 75 cm: beyond this width, airtightness may decrease. The cost of movable mullion  windows is 10 % or higher than that of traditional impost structures due to more complex hardware. A mosquito net can only be installed across the entire opening, and this requires special fasteners. Ventilation is only possible through the active sash.
Where are such windows particularly suitable? On balconies and terraces, in rooms with panoramic views, in wide window units, and door openings. If a free opening, aesthetics, and enhanced security are important to you, stulp windows can be the optimal solution — provided you are prepared to consider their specific features and slightly higher cost.