What is a threshold?
A threshold is the bottom rail of a door frame, or a raised element at the base of an opening that acts as a seal, water barrier or guide. It forms the transition between two rooms, or between inside and outside.
Function of a threshold
A threshold serves several purposes:
- Water barrier — prevents rain or cleaning water from running inside or outside
- Draught barrier — closes the gap between the door and the floor
- Sound barrier — reduces sound transmission between rooms
- Guide — for sliding doors, the threshold guides the sliding profile
- Structural — bottom member of the door frame
Applications
External threshold
For front and back doors, a watertight threshold is essential. Common materials:
- Hardstone or granite — durable and water-repellent
- Concrete — often with a sloped, water-shedding shape
- Aluminium — used on modern frames, often with a thermal break
- Plastic — low maintenance
Internal threshold
Between rooms with different floor materials (laminate to tile) a transition strip or threshold is used. Often made of brass, aluminium or wood.
Low threshold
For wheelchair accessibility a flush or very low threshold (≤ 20 mm) is important. Building codes set requirements for accessibility in new construction.
Shower threshold
Walk-in showers are often built without a threshold; drainage is provided by a slope in the floor.
Related terms
- Sill
- Drip sill
- Bottom rail
- Door frame
- Walk-in shower
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