Levelling and Scribing Kitchen Units

Nineteen at the bottom, four at the top

The end panel is offered up at the end of the run and held plumb. At the top the gap behind it is 4 mm. At the bottom it is 19. The wall leans out fifteen millimetres over 720, which is nothing anyone notices standing in the room and everything once a flat panel is stood against it. The panel is flat because a beam saw cut it flat; the wall is what a plasterer left in 1974.

Two operations decide where that fifteen millimetres ends up. Levelling puts the room's vertical error into the adjustable legs, where nobody ever sees it. Scribing puts the horizontal error into the back edge of a panel, where it becomes a line touching the wall along its length instead of a wedge of shadow. Everything downstream — door gaps, drawer alignment, whether the worktop sits on eleven boxes or on the two highest — inherits what those two decided, and none of it is fixable later without taking something back out.

What follows assumes the room has been set out already: a level line struck round the walls, the runs chalked on the floor, the services located, the floor build-up written on the plaster. That is a separate afternoon with a laser in an empty room and it belongs to its own guide. This one starts where that one stops — boxes in the hall, marks on the wall, first leg about to be wound.

What a levelled box is level in

Put a spirit level across a base carcase, get the bubble central, and you have proved one thing. There are three independent ways a single box can be out, and two further checks that are not about one box at all, and a fitter who tests only the obvious one produces a run that is level and still wrong.

Along the run is the axis everybody checks, and the failure it causes is not the expected one. Two adjacent boxes can each be level to a bubble and still sit at different heights: a step of a millimetre puts the worktop bearing on one and not the other, and puts two drawer fronts meant to read as a pair out of line at eye level. Level the run as a joined ladder instead — clamp and bolt each new carcase to the one already set, front edges flush, wind it, then check both tops with a straightedge long enough to span them.

Across the depth is the axis nobody photographs. A box tipped backwards by a degree hangs every door out of plumb and, more expensively, throws the runners. Concealed and undermount runners work in a carcase level front to back within the tolerance their manufacturer publishes, and the symptom of exceeding it is a drawer that closes itself, or one whose soft-close never engages. Blum, Hettich and Grass all state a figure and not the same one. A tipped box is what you get for free when a run is pushed hard back against a leaning wall and the legs are left where they were.

Racking is the third and the only one that cannot be corrected later. A flat-pack carcase assembled on an uneven floor, or dragged out of true by a fixing pulled tight into a hollow, becomes a parallelogram: still level, its opening no longer square. A door hung in one tapers against its neighbour whatever you do, because a cup hinge translates a door in three straight lines and cannot rotate it. Check both diagonals of the opening before the back is pinned, and again once the box is bolted to its neighbour.

Where the height comes from, and how much of it actually moves

Finished worktop height is a sum of three components and only one of them adjusts. The carcase is a fixed dimension off a beam saw and the worktop a fixed thickness. Between them sits the leg. The coordinating dimensions that make those three add up to a conventional working height — around 900 mm in European practice, 36 in in North American — are the subject of BS EN 1116, worth knowing because it explains why every maker's boxes land within a few millimetres of each other and why none are identical.

The trap is that a leg's nominal height is not its adjustment range. A leg sold as 150 mm gives a nominal 150 and a published travel either side of it, and that travel is a small fraction of the nominal figure. Häfele and Blum both print it for each leg and socket type, and it differs between systems and between the same system's 100 and 150 mm variants. Read it off the sheet for the legs actually in the boxes, because whether this room can be levelled at all is that one figure against the fall you measured.

Packing goes under the foot, never under the carcase. A packer slid beneath a gable that is not directly under a leg does nothing once the box is loaded — the load path is four point loads through four feet, and the base panel between them is not a bearing surface. Use rigid full-bearing packers, not folded offcuts. Where the floor is soft, meaning cushioned vinyl or an old covering left down, those four point loads find their way into it over the first year and take the run back out of level. That is an argument for cutting the covering away under the legs, not for winding them harder.

1. Wind every leg to the same nominal starting height on the bench, so the run arrives at the wall already parallel to itself.
2. Set the box standing on the highest point of the floor first, to the level line, legs near their shortest useful setting — everything else winds up from there rather than down into travel it has not got.
3. Work outward from it, bolting each new carcase to the one already set with front edges and tops flush, then winding the new one to the line.
4. Check across each new pair of tops with a straightedge before moving on: two boxes each level to a bubble can still be a millimetre apart in height.
5. Record the leg setting on the highest and lowest boxes in pencil inside a carcase, so whoever lifts this kitchen next knows which way the floor ran.

Scribing is subtraction, and there is no second cut

Five things get scribed in a normal kitchen, to three different surfaces. End panels and fillers to a wall that leans or bows. Plinths to a floor that falls or rolls. Cornice, pelmet and light rail to a wall or occasionally a ceiling. The worktop's back edge to the wall as well, though on laminate that operation belongs with the jointing and is covered there. What they share is that everything taken off is gone, and that the cut is made against a line existing only while the panel is held in the position it will finish in.

The geometry differs from coping a moulding into an internal corner, the scribe most carpenters learn first and the one the skirting guide works through. There the shape being followed is the moulding's own profile and the wall is incidental. Here the shape is the wall, the panel is flat, and the operation is the transfer of an irregular line onto a straight edge. Set dividers or a scribing block to the widest gap anywhere along the junction — not the average, and not the gap where you happened to hold it — hold the panel plumb at its final projection from the run, and run the point along the wall with the pencil following on the panel. Every part of the panel then loses something, which is what makes the line continuous.

Cut on the waste side and undercut behind the face. A back-bevel of a few degrees means only the front arris touches, so the joint closes tight along its visible edge and the material behind is not fighting for the last half millimetre. A down-cutting jigsaw blade takes the bulk off a melamine-faced panel without chipping it; a block plane or a belt sander takes the rest. Offer it up dry, find the two or three high spots holding it off, and take those back rather than running the whole edge again.

The last point turns a scribe into a layout decision. A scribe removes only material that is there to remove. An end panel has a limited width to give up before the run behind it shows, and a filler is only as wide as the one you were sent. Measure the widest gap before cutting anything, top and bottom, and compare it with what the strip has got. Where the wall eats the whole allowance the answer is to move the run, order a wider strip or take a unit out — not to cut the panel to nothing at one end and hope. A phone call on the day, a return visit if it is left.

1. Set and fix the run's front line first, so the panel is scribed from a position that will not move afterwards.
2. Hold the panel plumb in both directions, packed off the wall by the widest gap, before a mark is made.
3. Lock the dividers at that widest gap and mark the waste side clearly — a cut on the wrong side of the line adds the wall's shape to the panel instead of taking it off.
4. Cut proud, undercut behind the face, bring it back on the dry fit, and seal any raw core edge before the panel goes on for good.

The screw has to reach something

Wall units are the only part of a kitchen capable of injuring somebody, and the load is not the one people picture while hanging them. A run of them fills with crockery, tins and small appliances, and the fixings end up in axial withdrawal from a vertical surface with a lever arm out to the cabinet front. ANSI/KCMA A161.1, the North American standard for kitchen and vanity cabinets, includes a mounting load test for exactly that condition, and BS EN 14749 covers the same ground in Britain and Europe. Neither tests your wall. The cabinet arrives already proved; the fixing is the part nobody certifies.

Which anchor suits which substrate, how to find the timber and what a cavity fixing is genuinely rated for are worked through on the guide to fixing heavy things into plasterboard, and none of it is re-argued here. Two consequences are specific to a kitchen. The first is arithmetic: on dot-and-dab lining the screw has to cross the board, cross the adhesive void and still reach full embedment in the masonry, so its length is the sum of three numbers and the middle one comes from a test hole rather than an assumption, because it varies along one wall. The second is why a proprietary hanging rail earns its price, and it is not that the rail is stronger. It converts fixings pinned to cabinet-side positions into a continuous member you can fix wherever the structure actually is — which, on a wall where the studs, the dabs and the cabinet joints do not agree, is the difference between four good fixings and two.

Before any of it, know what is in the wall. Section 522.6 of BS 7671 sets out what is required of a cable concealed in a wall at less than 50 mm from the surface — the permitted zones it may run in, and the protection required outside them. In the United States, Section 300.4(D) of the National Electrical Code requires cables parallel to framing members to sit an inch and a quarter back from the face or be protected by a steel plate. Both assume somebody will drill, and neither helps where the run was put in by a previous occupant. Photographs taken before the boards went on are the cheap answer; a detector and a shallow first hole is what is left when nobody took any.

Doors last, and never to correct a box

A European cup hinge adjusts in three axes — depth, height and lateral — each a straight-line translation of the door relative to the carcase. The makers publish which screw does what and in what order, and the order matters because two of the three interact. What no hinge does is rotate a door into square. Take that as the operating rule for the whole stage: if a reveal tapers top to bottom, the box is out and the hinge is not the tool. Check the diagonals, check it is plumb across the depth, correct the box, and only then touch a hinge.

Reveals — the gaps between adjacent doors and drawer fronts — are trade convention rather than standard, commonly around three millimetres on contemporary slab fronts and set by the system's own drilling pattern in any case. The figure matters far less than holding one figure across every gap in the room, which is why it belongs on a gauge block rather than in the eye of somebody who has been in this room since seven.

Then do the opposite and use the eye deliberately. Stand in the doorway, at the distance someone entering will stand, and look along the run in whatever light the window gives. A taper of half a millimetre over a 700 mm door is invisible with a tape and obvious in raking light. The same walk finds a drawer front proud of its neighbours, a cornice mitre with a shadow in it, and a plinth scribed at one end and left square at the other.

1. Hang doors and fit drawer fronts only once every carcase is fixed, levelled and proved square, and after the worktop is on where the programme allows.
2. Set the depth adjustment on every hinge in a run to the same starting position before adjusting any individually.
3. Work left to right, setting each door against its neighbour with a gauge block rather than against the carcase edge.
4. Check each reveal top and bottom — a parallel gap of the wrong size is a hinge job, a tapered one is a carcase job.
5. Run every drawer to its stop and back before the plinths go on and the runners stop being reachable.

Before the van goes

The last half hour is worth more than any before it, because everything found in it is still cheap. Open every door and drawer to its stop. Put a flat hand across each carcase joint in both directions, since a fingertip resolves a step an eye standing up does not. Look along the front edge from the doorway. Push the run at one end and see whether anything moves. Check every plinth clip has engaged rather than been pressed near.

Then leave the room able to explain itself. Write the finished worktop height and the plinth height, both referred to the level line rather than the floor, in pencil inside a cupboard where the next trade will find them, and note which end the floor fell towards. Somebody will lay a new covering here in eight years and have to decide whether the dishwasher still comes out; that note and the appliance instructions left in a drawer are the difference between a five-minute answer and a cut floor.