How do I join two floors of different heights?

The profile you need depends on the height difference and whether both floors move. Getting the fixing method right matters as much as choosing the strip.

Difficulty: beginner
Time: 40 min
Read: 3 min
Safety: caution

Short answer

Equal heights take a flat or T-shaped profile. Unequal heights take a ramp or a lapped profile that covers the step. Both floors need their expansion gap preserved underneath, so the strip must be fixed to the subfloor between them rather than through either floor.

Doorways are where two floors meet, and they are also where floating floors need room to move. That combination is why threshold strips are fiddly: the strip has to cover the gap, tolerate movement on both sides, take being walked on, and not become the thing everybody trips over.

Safety

A change of level in a doorway is a trip hazard, particularly at the top of stairs, in a hallway or anywhere used at night. A ramped profile is safer than a step, and a small step is more dangerous than a large one because it is less visible.

Which threshold profile suits which change in floor height

Step by step

Measure the actual height difference.Lay a straightedge across the doorway from one floor to the other and measure the step. A few millimetres and a few centimetres call for completely different profiles.
Choose the profile from the difference.Level floors of the same type take a flat cover strip. Two floating floors of the same height take a T-bar that sits in the gap between them. A modest step takes a ramp. A larger step takes a lapped or reducer profile that laps over the lower floor.
Keep the expansion gap under the strip.Both floating floors need to move. The gap must remain open beneath the profile, which is why these strips are fixed to a base rail or to the subfloor and never screwed through the flooring itself.
Fix into the subfloor, and check what is underneath first.Doorways are exactly where pipes and cables run. Establish what is under the threshold before drilling. On a concrete floor, drill and plug; on timber, screw into a joist or noggin if you can.
Position the join under the closed door.The strip should sit under the door leaf when it is shut, so neither room shows the transition. That is usually directly beneath the closed door, not at the edge of the lining.
Cut the profile to fit between the linings.It should fit neatly between the door stops or the linings rather than running past them. Cut it slightly short rather than forcing it, so it is not under compression.
Check the door still clears it.The strip stands proud of both floors. This is a common reason a door starts catching after new flooring, and the time to find out is before the door is rehung.
Prefer a ramp to a step wherever you can.A sloped transition is safer, easier to vacuum over, and far kinder to anyone with mobility difficulties or a wheeled anything.

Tips

Where the height difference is large, consider whether the lower floor can be built up instead. A ramp in a doorway is a compromise, not an ideal.
Two-part profiles with a base rail are considerably easier to fit square than one-piece strips that must be positioned and fixed at once.

Common mistakes

Screwing the strip through the flooring. — It pins the floating floor at that point. The floor then cannot move as designed, and it buckles or opens gaps elsewhere.
Closing the expansion gap with filler or adhesive under the strip. — Same result. The gap exists so the floor can expand; filling it defeats the entire design.

Questions people ask

Can I avoid a strip entirely?

Between two glued or nailed floors of the same height, sometimes. Between floating floors, rarely — the expansion gap has to be covered by something.

What if the difference is very large?

That is a step, not a threshold, and it should be designed as one: consistent height, visible, and ideally not in a doorway. Very large differences are worth building up rather than ramping.