Carcass construction

In short

1. 01The top and bottom can sit between the side panels or over them. Between the sides the board is shorter by two side thicknesses, and over them the sides are lower by the board thickness.
2. 02When a board rests on the edges of the side panels, a load from above goes straight into the sides. A board between the sides is held by the joints.
3. 03A back can be laid on, rebated or grooved. A grooved back is set in from the back edge, so there is room behind it for an uneven wall and cables.
4. 04The back braces the carcass, so it cannot rack out of square.
5. 05Instead of a full top board, a base unit has two cross rails that the worktop sits on. A rail standing on its edge is stiffer than one lying flat.
6. 06Shelf sag grows fast with the span. With the same load per metre, a shelf twice as long sags about 16 times more. A thicker board, a support or a divider helps, and a tall carcass needs at least one fixed shelf.