Figure 1a - Base cabinets on either side of dishwasher
Dishwashers require a gap in the cabinetry of 24″.
If you are installing a dishwasher in the middle of a base cabinet then you will be constructing two base cabinets, one on each side of the dishwasher, as shown in Figure 1a. The countertop will cover both cabinets and the dishwasher.
I prefer to have a finished kitchen floor under the cabinets. By building on a finished floor, the countertop height will be at the conventional level and the installation of built-in dishwashers, is much easier. However that is not critical and the cabinets can be built on the sub-floor and the kitchen floor finished later.
NOTE: It is best to do all plumbing and electrical rough-in, prior to starting the cabinet construction.
We will start the construction with base cabinetry that is to be built wall to wall as shown in Figure 1.
Figure 1 - Kitchen area emptied for construction of base cabinets
The construction of the base cabinets starts with building a base, which provides support for the bottom of the cabinet and provides the toe kick, Figure 2 & 2a.
The base unit can be constructed from particle board with a laminate veneer or, plywood with a wood veneer for the front, depending on the finished cabinet appearance, cut so that the finished height is 4 1/2″. The sides and back can be constructed from construction grade 1 X 6 cut to size or you can use 1 X 4 having the top of the lumber at the 4 1/2″ height and the bottom not resting on the floor. It is only important that the front toe kick board rests on the floor.
In many cases, using shorter pieces of lumber on the back and sides makes leveling the base support much easier.
Figure 2 - Building the bottom support, including toe kick, for the construction of the kitchen base cabinet
The leveling of the base support assembly is critical, as the level of the countertop depends on this support being level. Use cedar or composite shims, as shown in Figure 2c, to maintain the level on the front of the base support.
Figure 2c - Composite shims for leveling cabinet base
Screw the sides and back of the support to the walls, preferably into studs.
The finished depth of the base support should be 21″ and the height should be 4 1/2″.
Use cross supports every 4' as shown in Figure 2a.
Figure 2a - kitchen base cabinet construction bottom toe kick