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Cross-market term

Threshold and door sill

The assembly at the bottom of a doorway: the piece the door closes onto, the weathering at an external door, and the transition between two floor finishes.
  • 4Markets
  • NoSame thing everywhere
  • 3Calculators

What it is called, by market

One concept, four markets. Where a name means something else locally, the card says so rather than leaving you to find out on site.

  • United Kingdom

    Close, not identical

    threshold

    also cill, weather bar, door bar, transition strip, level threshold

    One word for the whole condition. A LEVEL threshold is a specific accessibility requirement with a maximum upstand, and is a different product from a weathered one.

  • Australia

    Close, not identical

    threshold

    also door sill, weather bar, transition strip

    As the UK, with sill used more freely for the external weathering component.

  • United Statesyours

    Same word, different thing

    threshold

    also saddle, door sill, transition strip, sill pan

    SADDLE is the interior piece between two rooms; SILL is the exterior weathering component — and sill also means the sill plate on the foundation and the window sill, so it needs qualifying every time.

  • Canada

    Same word, different thing

    threshold

    also saddle, sill, sill pan, transition

    As the United States, with the sill PAN — a preformed tray under an exterior door — a standard item that British practice details as a DPC tray instead.

The governing standard, by market

  • United Kingdom

    Approved Document M / Approved Document Q

    Access to and use of buildings including accessible thresholds, and security requirements for doorsets.

  • United States

    IRC R311.3 / ADA 404.2.5

    Landings at required exterior doors and threshold height limits, and accessible threshold requirements.

Calculators for this

Each works in either measurement system, and the terminology on the page follows whichever market you have selected.

Floor Transition Strip Calculator →Weatherstripping Calculator →Door & Window Casing Calculator →

Frequently asked questions

What is a level threshold, and why is it hard?
It is an external doorway with essentially no step — accessibility guidance limits the upstand to a very small dimension — and it is hard because it asks one detail to do two contradictory things. A threshold keeps water out by being higher than the water, and a level threshold is not allowed to be. The resolution is drainage rather than height: a drainage channel immediately outside, a falls arrangement taking water away, and often a proprietary threshold with a concealed drained chamber. That is a considerably more expensive detail than a step, it requires the external level to be set correctly during construction rather than adjusted afterwards, and it is the single most common source of water ingress at an accessible entrance. Specifying a level threshold without the drainage is specifying a leak.
Why does an external door need a pan or a tray beneath it?
Because the threshold is a horizontal joint at the bottom of a wall, which is where water collects and where it has the longest time to find a way in. Any water that gets past the door's own weathering — driven rain, a failed seal, snow melting against the frame — lands on the structure directly under the threshold, and without something to catch it, it soaks into the floor structure or the wall below. American practice answers with a SILL PAN: a preformed or site-formed tray with upturned back and ends, sealed to the drainage plane, that catches whatever gets through and returns it outward. British practice detailed the same thing as a cavity tray with stop ends. Either way the failure is identical when it is missing, and it appears as rot in the floor beside the door rather than as a visible leak.
How is the internal transition different from the external one?
It is doing a finish job rather than a weathering one, and it is sized by the two floors it joins. An internal threshold — the saddle, the transition strip, the door bar — bridges between two coverings that may differ in thickness, in how they move, and in what they need at their edge. A floating floor needs its expansion gap maintained at the doorway, so the strip has to cover a gap rather than clamp the floor; a carpet needs gripping; tile needs its edge protected. That is why transition strips come in families rather than as one product, and why running a floating floor straight through a doorway under a decorative strip that pins it is one of the commonest causes of a floor peaking further into the room.