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Setting Cabinets on Uneven Floors
Almost no floor is perfectly flat, and a cabinet installer plans for that. The method is to find the highest point along the run, set the first base cabinet there, and then raise every other box to match using shims, so the tops of all the cabinets lie in one level plane. The floor underneath may dip, slope or wave, but the countertop surface will not.
Why floors are not flat
Floors move. Wooden joists sag a little under years of load, concrete slabs settle and crack, and the pad the house sits on shifts with soil and moisture. Older bungalows in the Wood Streets and Casa Blanca sit on raised foundations whose posts have settled at different rates, so a floor can slope noticeably from one side of a kitchen to the other. Newer tract homes in Orangecrest and La Sierra are built on slabs that are generally flatter, but they are rarely perfect, and builders pour them with tolerances that leave small waves.
The floor does not have to be right for the kitchen to be right. What matters is that the cabinets are level and plumb, because the countertop, the sink and the appliances all depend on a flat plane. A cabinet that follows the slope of the floor will have doors that drift and a stone top that rocks.
Find the high point first
The installer begins by locating the highest spot on the floor where cabinets will sit. A long level, a straight edge or a laser level shows where the floor rises and falls. The reading is taken along each wall and across the room. The highest point sets the datum, the reference from which everything else is measured, because it is easier to raise the other cabinets with shims than to lower the high one.
A line is drawn on the wall at the height of the top of the base cabinets, measured up from the high point. This line is the target. Every box in the run must end up with its top edge touching it. Starting here prevents the common mistake of beginning at a low corner and discovering that the last cabinet is far above the line.
Shimming the bases
Shims are thin wedges of wood or plastic. Placed under the base cabinet, usually beneath the toe kick or the bottom rail, they lift the box until its top meets the line. The installer slides pairs of opposing wedges to fine tune the height, checks level front to back and side to side, and repeats until the cabinet is true. Several shim points are used so the weight is distributed and the cabinet does not rack.
Solid shims matter. Cheap or compressible material can crush under weight over time, especially under a heavy stone top and a loaded cabinet. Composite shims and hardwood wedges hold their shape. The installer also places shims behind the cabinet at the screw points, so tightening the screws does not pull the box out of square.
Joining cabinets before fastening
Once the first cabinet is level and plumb, its neighbor is set against it. The faces are aligned, clamped and screwed together through the adjoining frames, with the screws countersunk so they do not interfere with the doors. Then the second cabinet is leveled, usually by adjusting its own shims. Joining before fastening to the wall lets the installer correct small differences between boxes by drawing them together.
Many modern cabinets have adjustable legs that thread up and down, which makes leveling quicker. Even then, the installer checks each leg, as a leg set too far can lift the cabinet away from the floor and leave an uneven toe kick. Boxes without legs rely entirely on shims and a scribed toe kick board.
Handling a slope across the room
Sometimes the floor slopes enough that shimming creates large gaps under the cabinets. A gap of a quarter inch is routine, while one of an inch or more calls for a different approach. The toe kick, the board that covers the gap, can be cut or scribed to follow the floor. A strip of flexible trim or a shoe mould can hide small irregularities as well.
In extreme cases, the floor itself may be leveled before the cabinets go in. Self leveling compound on a slab or a layer of plywood and shims on a wood floor can bring the surface closer to flat. This adds time and expense, so it is used when the slope is large enough to compromise the installation or when the new floor requires a smooth subfloor anyway.
Dealing with out of square walls
Floors and walls misbehave together. A wall that leans or bows causes the back of the cabinet to touch it at one point and leave a gap at another. Shims behind the cabinet fill the gaps, and the fasteners pull the cabinet into its true position. The countertop will later be cut to match the actual shape of the wall, a scribing process that the stone fabricator handles carefully.
The installer keeps the front faces of the cabinets in a straight line even if the wall is crooked, because that line is what the eye reads. Gaps at the back, behind the stone and the backsplash, are out of sight and easily filled.
Checking before the stone arrives
When all the bases are set, the installer checks the entire run. A long straight edge laid across the tops should show no gaps, and a level should read true in every direction. Diagonals across any island are measured to confirm squareness. Adjustments are made now, because the stone fabricator will measure the finished cabinets and cut the top accordingly. A cabinet that is a fraction low will leave a void under the stone, which may require shimming and can crack the top if left unsupported.
The check takes only a few minutes and is the best insurance against a fitting problem later. It is also reassuring for the owner to watch, since a level bubble sitting dead center is easy to understand.
What owners can look for
- Doors and drawers that line up evenly with consistent gaps.
- A level that reads true on the top of each cabinet.
- No visible rocking when pressing on the corners of a base cabinet.
- Toe kicks that follow the floor without large gaps.
- Screws that are tight and heads that are sunk or covered.
An uneven floor is not a defect in the house, and it is not a barrier to a good kitchen. It is a normal condition that a skilled installer expects and corrects. The visible result, a straight line of cabinets with a flat top, hides all that careful adjustment beneath.