Fluted, reeded and slatted profiles

At a glance

Sizes in the drawings and worked examples are our illustrations, in millimetres. No standard fixes them.

Four profiles, one set of numbers

Fluting is a row of shallow hollows. The edge where two hollows meet in a point is called an arris, and a flat band between two hollows is a fillet (Wikipedia, Fluting (architecture), which also gives classical columns 20 or 24 flutes). We call the flat between two flutes the land, because it is the word that works on a drawing of a panel. Reeding is the opposite: a row of convex ridges. A V-groove is a straight-sided cut, a square channel a rectangular one, and a slatted wall is a row of separate battens, usually over a backing.

Sellers use “fluted” for all of these, so ask for the drawing. The drawing here repeats at one pitch so the four can be compared; the shapes of single mouldings are on our moulding profiles sheet, and how a whole wall is divided into panels is on the wall panelling set-out sheet. This sheet divides a panel, or a wall of board panelling, into flutes.

Five numbers and what follows from them

Five numbers describe a fluted, reeded or slatted face, and every other figure follows from them.

• Pitch p: one repeat, centre to centre. It equals the width plus the land.
• Width w: the flute, reed or slat across the face.
• Land l: the flat left between two flutes (for a slatted wall, the gap).
• Depth d: how far a flute is cut below the land, or how far a reed stands above its valley.
• Thickness t: the board. What is left under a flute is the web, t less d.

For a flute that is a single circular arc, the radius is R = (w²/4 + d²) / 2d, which is also the radius of the cutter. The deepest a single arc can go is half the width: a semicircle, with d = w/2 and R = w/2. The drawing shows three 20 mm flutes in an 18 mm board, and the table gives the arithmetic. The web is what keeps the board whole and what takes the knocks at an edge. We found no source that sets a minimum web, a minimum land or a limit on depth, so the drawing, the cutter and the partner joiner settle them, and a mock-up confirms them.

What our live fluted panels page gives. The fluted wood panels page shows three profiles, soft reed, deep flute and square channel, in sheets 3,050 x 1,200 mm and 5 mm thick as standard (engineered panels also in 3.5 and 8.5 mm). Each section drawing carries one marked dimension: 12 mm, 17 mm and 5 mm. The page does not say what they measure, and the drawings are not to scale. If 12 mm and 17 mm are the repeats of the reed and the flute, then across a 1,200 mm sheet 12 mm goes 100 times exactly, but 17 mm goes 70.59 times: a sheet cut at 1,200 mm would end part-way through a flute. Cut it to 70 repeats (1,190 mm), or set the sheet joints on flute centres. The 5 mm marked on the square channel looks like the width of one rib, not a pitch. Ask the partner for the pitch, width and depth of each profile before relying on any of this.

Setting out a wall: whole flutes and equal lands

A wall of flutes looks right when the pattern is the same at both ends and sits square to the centre of the room. That needs a whole number of flutes, equal lands, and edge strips the same width as a land. Take a wall 2,963 mm wide, 20 mm flutes and a target land of 4 mm.

1. Take the finished width W between finished faces, after scribing (see the joinery tolerances sheet).
2. Choose the flute width w and a target land: here 20 and 4 mm.
3. Count the flutes: n is the whole number nearest (W − target land) / (w + target land). Here (2,963 − 4) / 24 = 123.3, so n = 123.
4. Work out the land: land = (W − n x w) / (n + 1). Here (2,963 − 2,460) / 124 = 4.056 mm. The two edge strips are the same width, so the pattern is the same at both ends.
5. Check the change: 4.056 mm against 4 mm is +1.4 per cent on the land and +0.24 per cent on the pitch (24.056 against 24 mm), far too small to see. Agree a limit with the designer before counting.
6. Centre it. With an odd count the middle flute sits on the centre line (flute 62 of 123); with an even count a land does. Choose the one that suits the centre feature, a door, a fireplace or a window.

The same wall with other counts shows why 123 is the right one: it changes the land least.

If the cutter fixes the pitch. A gang of cutters cannot stretch the land. Then keep 4 mm lands, count 123 flutes, and let the edge strips take the remainder: 7.5 mm at each end against 4 mm between flutes. It is less even than the stretched land, so decide which the designer prefers.

Sheets. A 1,200 mm sheet cannot span the wall. Run the joints down the centres of flutes 42 and 82, symmetrical about flute 62, so that the three sheets are 1,000.4, 962.3 and 1,000.4 mm wide. A joint down the middle of a hollow sits in its shadow; one through a 4 mm land shows. This is our reasoning, to be confirmed by the partner joiner.

A flush door in the wall. Cut the leaf and its frame down flute centre lines, so that the gap hides in a hollow. A leaf 36 pitches wide, less a 3 mm gap, is 36 x 24.056 − 3 = 863.0 mm. Size the leaf to the pattern, not the pattern to a stock leaf.

Corners, ends and joints

At an external corner a flute can leave the arris thin. With a land on the corner (A) the arris keeps the full 18 mm. With a flute on the corner (B), the 45 degree mitre meets the face where the hollow has already cut the board away, and in our drawing the board is about 13.1 mm thick there, 27 per cent less than 18 mm. Sharp arrises are the first thing knocked off on site, so draw a land on external corners.

• Internal corners. The second board butts the first. Start each wall with its own edge strip, equal to a land, and check the corner for square before the count is fixed.
• Ends. Where the pattern stops at a skirting, a cornice or a reveal, finish on a whole flute or a whole land, never part of one. Mark where it stops at the top and the bottom on the elevation.
• Returns. At a window reveal, set the count from the return back, so the pattern runs round without a short flute.
• Joints. Put sheet joints through flute centres, as above. For a slatted wall the joint is a gap, so make it the same as the others.

Substrates, finish, fire and sound

• What is cut. Ask what the flute is cut into: solid timber, MDF with a veneer over the profile, or a laminated sheet. The web, the movement and the finish differ for each. See the MDF decoded, veneer specification and timber movement sheets.
• Finish. A spray or a brush reaches the hollow differently from the crest, and our fluted panels page notes that a coating takes differently in the grooves. Sample the finish on the actual profile; see finishes on timber joinery.
• Fire. In England a panelled wall is a lining and meets Table 6.1 of Approved Document B. The generic fire list for solid timber panelling limits how much of the face may be profiled, so on our reading a face fluted from edge to edge is outside it, and a thin sheet is thinner than its minimums. Ask for a classification for the fluted build-up as installed. The fire performance of wall panelling sheet sets out the evidence.
• Sound. Slatted and fluted walls are often chosen for acoustics, but absorption depends on the whole assembly, felt, cavity and backing, and on test data for it. We give no figures.

We coordinate the profile drawing, the set-out and a mock-up with the partner workshop that will produce the panelling, before the schedule is fixed. See wall panelling styles for how these faces sit among the other styles.

Ref [P-03]: [fluted / reeded] panelling, profile as detail [D-31] at 1:1: flute width [20] mm, land [4] mm, depth [6] mm, board [18] mm thick, web at the flute root not less than [12] mm. Set out symmetrically about [the centre line of the chimney breast], whole flutes only, edge strips equal to the land, land adjusted by not more than [2] per cent from the nominal [4] mm. Sheet joints down flute centres. External corners [mitred with a land on the arris]. Finish [ ]. A [600] mm wide full-height sample, set out as drawn, to be approved before production.

Ref [P-04]: slatted panelling, slats [18 x 12] mm at [24] mm pitch ([6] mm gap) on [ ] mm backing board, the backing finished [black / to match] so the gap reads as shadow. Set out from the centre line, whole slats only, end gap equal to the slat gap. Slat ends [square / returned]. Substrate flat to [ ] mm over [2] m.

Door leaf and frame in the [fluted] wall cut down flute centre lines, so the [3] mm gap falls in a flute. Leaf width [36] pitches less the gap, [863] mm, from the drawing. Pattern to run unbroken across the leaf, frame and wall.

Standards and sources

• No standard fixes flute, reed or slat sizes: they come from the cutter, the board and the partner workshop.
• Wikipedia: Fluting (architecture): flute, arris and fillet.
• Make Bespoke Studio: Fluted wood panels: profiles and sheet sizes.
• Approved Document B Vol 2 Table 6.1; Decision 2006/213/EC: fire cross-reference only: see the fire performance sheet.

Questions we are asked

What is the difference between fluted and reeded?

Fluting is a row of concave hollows; reeding is a row of convex ridges, the opposite. Sellers often use “fluted” for both, so ask for the section drawing with the width, depth and pitch marked.

How deep can a flute be?

For a flute that is a single circular arc, no deeper than half its width, which is a semicircle. What limits it in practice is the web left under it: a 20 mm flute 6 mm deep in an 18 mm board leaves 12 mm; cut to 10 mm it leaves 8 mm. We found no source that sets a minimum, so ask the partner joiner.

How do I set out flutes so they look even across a wall?

Use a whole number of flutes, equal lands and edge strips the same width as a land. For a 2,963 mm wall with 20 mm flutes and a 4 mm target land, 123 flutes give a land of 4.056 mm, a change of about 1.4 per cent that cannot be seen. Put the centre flute, or the centre land, on the centre line.

Where should the joints between sheets go?

Down the centre of a flute, where the shadow of the hollow hides the line, rather than through a thin land where it shows. Cut the sheets to a whole number of flutes. This is our reasoning; the partner joiner confirms it.

Do fluted panels need to meet a fire class?

In England a panelled wall is a lining and has to meet Table 6.1 of Approved Document B, which asks for class B, C or D depending on the room. The generic list for solid timber panelling limits how much of the face may be profiled, so ask for a classification for the fluted build-up as installed. The fire performance sheet explains.

How wide should a slat and its gap be?

No standard says. The pitch is the slat plus the gap, for example 18 + 6 = 24 mm, and the set-out works as for flutes: a whole number of slats and a gap at each end equal to the others. Colour the backing so the gap reads as shadow.