Floor transitions and movement joints: wood, stone, carpet and brass

At a glance

Illustrative. Regulated figures: Approved Document M only. Movement gaps: a distributor's guidelines and our journal.

Wood to stone: one junction in section

Three things are settled together at every junction between two floors: the height, the movement and the line. The height is where regulation touches (next section). The movement is what cracks floors. The line is the design, and a thin brass or bronze strip is how many designers make it deliberate.

Timber moves with humidity. The distributor's installation guidelines read for this sheet ask for an expansion gap at the perimeter of a timber floor and at every abutment, and say thresholds must allow for expansion and contraction. Stone and screed do not take up that movement, so a timber-to-stone junction has to give the timber somewhere to go. One common answer is the detail drawn here: a metal T-section whose stem sits in the gap and whose head covers it, with the timber free to move beside the stem and the stone bedded up to it.

The two finished faces and the strip head sit at the same finished floor level (FFL). The build-ups under them are different thicknesses, so the base or the bed under one is made up to level. Set the junction out from FFL on the drawing, never from the top of the slab.

• Levels. Draw both build-ups and the make-up under each, with FFL marked, before the strip is chosen.
• The strip. Name the metal, the head width, the stem depth and the finish. If the timber will be sanded after the strip is fitted, ask the profile maker how much sanding the head allows.
• The stone side. The stone workshop and stone fixer decide whether the stem sits in the bed or in a movement joint; see natural stone flooring specification.

Common mistake: tidying the junction by filling the gap with adhesive or grout. Our wood flooring installation guide says the gap is covered, not filled.

Height: what Approved Document M says

Approved Document M gives guidance on meeting the access and use requirements of the Building Regulations in England. Volume 2 is for buildings other than dwellings, such as hotels, restaurants and offices; volume 1 is for dwellings. We read both and give only what they say about floor junctions.

Volume 2 says that a level threshold is preferred, especially for doors in frequent use (2.6). Volumes 1 and 2 give the same 15 mm and 5 mm figures; volume 1 says ‘chamfered’ where volume 2 says ‘chamfered or rounded’.

What we did not find. A height limit for an ordinary internal door threshold, or for the junction between two finishes inside a building. Volume 2 asks for no trip hazard where floor materials change (2.7(h), 2.29(e), 3.16(e)) but gives no number for it. If your project needs one, ask the accessibility consultant or the building control body what they will accept. BS 8300-2:2018 is the wider reference and was not read.

Fire doors. A threshold or strip under a fire-rated door can affect the gap that door was tested with. Confirm it with the door maker and the fire engineer: see the fire documentation matrix.

Whether an alteration to an existing floor triggers Part M is a question for building control. Approved Document M does not apply in Scotland, Wales or Northern Ireland in this form.

Movement: where the gaps go

Timber. A UK wood-flooring distributor's guidelines (January 2024) give a rule of thumb: an expansion gap of 1.5 mm per linear metre to the perimeter, with a minimum of 10 mm, subject to site conditions. They also ask for gaps at radiator pipes, thresholds, door linings and floor sockets, and for a threshold profile in every doorway, arch or narrow section between areas. Our wood flooring installation guide asks for a minimum of 15 mm around the perimeter and every vertical obstruction, for plank and pattern floors alike, and, for a fully bonded plank floor wider than 8 m, intermittent gaps of 1 mm for every metre beyond. Where the two differ, use the larger.

Doorways. Both sources put a threshold at the doorway that lets the floor move (our guide covers the gap with a T-section) and undercut door frames and architraves so the boards slide underneath. Heated floors. If only part of an open floor is heated, our underfloor heating guide breaks the floor with a threshold strip between the zones, because the two areas shrink and swell at different rates.

Stone. A stone floor needs perimeter joints and, across larger areas, intermediate joints through the full depth of stone, bed and screed (Tile Association, quoting BS 5385-3:2024 for external floor tiling; interior spacing is not given here). Draw them to line up with the joints in the base. The line. Where a movement joint and a pattern line can coincide, let them: a strip over a joint is the cheapest way to make the junction look chosen.

Four more junctions

• Wood to carpet. A cover strip fixed on the carpet side lets the timber slide under its lip. The carpet and its underlay should bring the face up to the timber, or the strip becomes a step.
• Doorway. A T-section under the leaf covers the gap that runs through the doorway. Door linings can be undercut, and architraves too, so the boards pass beneath them.
• Perimeter. The gap is covered by skirting, a scotia or a shadow gap, and the skirting is fixed so it does not trap the floor. See skirting and architrave heights.
• Hearth. Where no scotia or bead can be fixed, for example in front of a stone fireplace, the distributor's guidelines allow a cork expansion strip or a mastic joint. Hearth construction and clearances are Approved Document J matters and are not covered here.

Brass, bronze and stainless strips

Our metal inlay guide calls brass the default for a floor line: warm, kind to work and steady with age. Bronze runs darker and takes patina; nickel silver and stainless steel give a cooler, silvery line. Each can be finished bright, satin, brushed or chemically darkened. See brass alloys explained for the metals.

A strip in a floor is walked on every day, so choose its finish for wear as well as colour. Our lacquered vs unlacquered brass and copper sheet found no independent durability data for lacquer on handled brass, so ask the metal workshop what it expects and agree a sample.

Profile makers publish stock sizes, and a stock profile is usually the cheaper route. As an example, one movement profile with a brass or chrome insert is listed with a 7 mm joint width and heights of 6 or 9 mm. A strip made to a drawing is a metalwork enquiry: see metal inlay joinery.

Where Approved Document M applies [volume 2 / volume 1] and the entrance is an accessible entrance: threshold level or, if a raised threshold is unavoidable, not more than 15 mm total height, with a minimum number of upstands and slopes and any upstand higher than 5 mm chamfered or rounded (volume 2, paragraph 2.7(e)) [confirm current edition]. Changes in floor material at the entrance not to create a trip hazard.

Junction between [timber] and [stone] at [location ref] by [brass T-section], head [ ] mm wide, stem [ ] mm deep, finish [ ], over an expansion gap of [ ] mm on the timber side. Timber, strip head and stone flush at FFL [ ] m. Stone bedded independently up to the stem. Detail drawing [ref] approved before fabrication.

Expansion gap of [15] mm minimum around the perimeter and every vertical obstruction, covered by [skirting / scotia / shadow gap] and never filled with adhesive or grout. Gaps through doorways covered by [T-section]; door linings and architraves undercut where agreed. At [hearth]: [cork strip / mastic joint], [ ] mm.

A mock-up of each junction type built with the real finishes and strips, approved by [designer] before the main work. Junctions under fire-rated doors confirmed by the door maker and [fire engineer] before fixing.

Standards and sources

• Approved Document M vol 2 (2015 ed. incl. 2020, 2024 amendments, England): read; paras 1.13(f), 2.6, 2.7, 2.29, 3.14, 3.16.
• Approved Document M vol 1 (2015 ed. incl. 2016 amendments, England): read; paragraph 1.14(b), Appendix A.
• BS 8300-2:2018, BS 8201:2011, BS 5385-3:2024: named; not read (BS 5385-3 only via the Tile Association, Jan 2025).
• A UK distributor's installation guidelines (Jan 2024, Nov 2022); our journal guides: read; gaps, thresholds, hearths.

Questions we are asked

How high can a threshold be?

For an accessible entrance to a building other than a dwelling, Approved Document M volume 2 (England) paragraph 2.7(e) asks for a level threshold or, if a raised one is unavoidable, a total height of not more than 15 mm, a minimum number of upstands and slopes, and any upstand higher than 5 mm chamfered or rounded. Volume 1 defines an accessible threshold for dwellings with the same 15 mm and 5 mm figures. Scotland, Wales and Northern Ireland have their own documents.

Is there a limit on the height difference between a wood floor and a stone or tile floor inside?

We found none. Approved Document M volume 2 asks that changes in floor material at entrances and lobbies do not create a trip hazard but gives no number for them. Aim for the two faces to be flush at the finished floor level, and ask the accessibility consultant or building control body what they will accept where it matters.

How wide should the expansion gap be at the edge of a wood floor?

A UK distributor's rule of thumb is 1.5 mm per linear metre to the perimeter with a minimum of 10 mm, and our own guide asks for at least 15 mm around the perimeter and every vertical obstruction. Use the larger, cover it with skirting, a scotia or a shadow gap, and never fill it.

Can I put a brass strip between wood and stone?

Yes, with the movement allowed for. One common detail is a T-section whose stem sits in the gap and whose head covers it, with the timber free to move beside the stem and the stone bedded up to it. Set the junction out from the finished floor level so the two faces and the strip head come out flush.

What goes between a wood floor and a stone hearth?

The distributor's guidelines allow a cork expansion strip or a mastic joint where no scotia or bead can be fixed, for example in front of a stone fireplace. Hearth construction and clearances are Approved Document J matters, which this sheet does not cover.

How do I handle a doorway between two rooms with wood floors?

Both the distributor's guidelines and our guide break the floor at the doorway with a threshold that lets the floor move, a T-section for example, and undercut door frames and architraves so the boards slide underneath. Where the door is fire-rated, confirm any threshold with the door maker.

What if only part of an open floor has underfloor heating?

Our underfloor heating guide breaks the floor with a threshold strip between the heated and unheated zones, because the two areas shrink and swell at different rates. The heating designer confirms where the break goes.