What is a drop-down door seal?
A drop-down door seal, also called an automatic door bottom, is a seal fitted at the base of a door that lowers onto the floor as the door closes and lifts again as it opens. It closes the gap under the door without a threshold or a seal dragging across the floor. In Dutch it is called a valdorpel.
How it works
A small plunger projects from the hinge end of the seal. As the door closes, the plunger presses against the frame and triggers a mechanism that lowers a rubber or brush strip. Most models have an adjusting screw to set how far the strip drops.
Types
- Mortice (concealed): fitted into a routed groove in the bottom edge of the door and almost invisible.
- Surface-mounted: screwed to the face of the door, so no routing, but visible.
- For glass doors: clamped to both faces of the glass.
Besides draughts, suitable versions keep out dust, noise or smoke, and there are versions intended for fire doors. Manufacturers quote acoustic ratings of around 50 dB for their best models; these are test figures, and the real result depends on the door leaf, the gap and the fitting.
Application
Drop-down seals are used where a threshold is unwanted or impractical: level access for wheelchairs and walking frames, doorways used by trolleys or beds, and interiors with a continuous floor finish. They suit both internal and external doors.
Tips and points of attention
- Length: match the length to the door width and have it cut to size where possible.
- Flat floor: the strip only seals on a flat, continuous surface. Over a groove or joint it will leak.
- Adjust carefully: set too low, it drags and wears; too high, and the draught remains.
- Fire doors: never rout a fire door for a seal without the door manufacturer’s approval, or its certification may be lost.
Related terms
- Draught strip
- Draught
- Threshold
- Door clearance
- Weighted sound reduction index
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