Automatic Door Bottoms: Adjust for Contact, Not Force

An automatic door-bottom seal drops as the door closes and retracts when it opens. Unlike a fixed sweep, it relies on an actuator meeting the frame. Extra drop is not a cure for a wrongly fitted unit.

Check the exact mechanism

Identify the model and its surface, semi-mortise or full-mortise mounting method. Check the maker's actuator position, clearance and permitted cutting end before machining. Pemko 411_RL instructions put the plunger at the hinge side and allow trimming only at the non-plunger end; those rules are not a universal cutting template.

Aim for contact, not force

For the 411_RL, Pemko says to adjust until the gasket just touches the sealing surface with the door closed. It warns that over-adjustment can damage internal parts and says not to use power tools for adjustment. Zero's instructions also warn against over-adjusting the models they cover.

After fitting to the exact instructions, open and close the door and check that the seal retracts and the door latches normally. If it drags or needs force, recheck the installation rather than extending the actuator further. For the 411_RL on a fire-labelled or special-construction door, Pemko says the door manufacturer must prepare the mortise.

For the wider picture, read our door-seal selection guide.

Sources: Pemko 411_RL sheet (81095, 6/25); Zero manufacturer resources (installation Rev. 03/19-d). Checked 13 November 2026. Cover: generic illustration.