Windlock

A windlock is a formed steel fitting mechanically fastened to the end of a curtain slat at predetermined intervals up the curtain of a rolling steel door. Its purpose is to hook behind or interlock with wind bars inside the vertical guides, holding the curtain edges firmly in the guide channel when wind loads push laterally on the door face.

Without windlocks, a rolling door curtain is held in its guides only by the weight of the curtain itself and the friction of the slat ends against the guide channel. A significant wind load, especially a negative-pressure suction load pulling the curtain outward, can lift and bow the curtain until the slat ends leave the guides entirely. Once the curtain loses guide contact, the door is compromised and the curtain can buckle or tear.

How windlocks engage the guide:

Each guide channel contains a wind bar, a steel rod running the full height of the guide on its inside face. The windlock fitting on the slat end wraps around or hooks behind the wind bar. This engagement converts the curtain's tendency to pull away from the jamb into a mechanical interlock. The wind bar resists the pullout force, and the guide assembly (which is fastened to the wall or jamb) transfers the load to the structure.

Windlock spacing is determined by the door's wind load specification. A door rated for a higher pounds-per-square-foot (PSF) design load will have windlocks at closer intervals than one rated for lower wind pressure. Engineers specify the number of windlocks per curtain width and the required guide engagement depth based on wind zone maps and local building codes per DASMA technical data.

On a large commercial door, windlocks may be placed every few slats on each side, with the total number depending on door height, curtain width, and the specified wind load. They add negligible weight but meaningfully increase the certified wind rating of the assembly.