Housing joint
Also called: housing, dado joint, dado, through housing, stopped housing, trench joint
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A housing joint cuts a slot across the grain of one piece of wood so that the end or edge of a second piece can drop into it and be held square and in line, the ordinary way of fitting a shelf into the side of a cupboard or bookcase. Fairham (1920) described the cut plainly as "a trench, groove, or housing is cut so as to receive the portion to be jointed". In American usage the same joint and the same slot are usually called a dado rather than a housing.
Through and stopped
The simplest choice is how far the slot runs. Fairham (1920) distinguished a housing that runs the whole width of the shelf, so it is visible where it meets the front edge, from a "stopped housing", where the groove stops a short distance short of the front edge so the housing cannot be seen once the joint is assembled. The through version is the faster one to cut, since it can be sawn to full depth in one pass, while the stopped version, worked blind at one end, takes more chisel work to finish but leaves a cleaner front edge. For extra grip, the sides of the slot can be angled rather than parallel. Ellis (1908) named the plain, straight-sided version a Plain Stopped Housing, and described a Straight Dovetail Housing cut with both sides angled to match, and a Tapered Dovetail Housing, where one end of the housing is cut wider than the other, "so that it shall tighten as it goes in". Both dovetail forms wedge the joint tight mechanically as it is driven home, rather than relying on glue alone. Wearing (2010) treated the dovetail and tapered dovetail housing as a step up from a beginner's basic skills, harder to lay out and cut accurately than a plain housing.
Cutting and fitting
Porter (1999) described marking the width of a housing by squaring lines across the board, then setting a marking gauge to scribe both the width and the depth, with the sides knifed in sharply before sawing so the saw has a clean line to follow. On a piece such as a shelf housed into an upright, the depth of the slot is commonly varied to suit the thickness of the piece being housed at that point, while the wood left beneath the slot is kept a constant thickness all along its length. A tight-sawn housing should need no further work: if the sawing is accurate the shelf fits first time, and Joyce (1987) advised that only if it runs a shade wide does the joint need easing at the sides, with an edge trimming plane or a chisel. Noll (2002) described cutting a small extra shoulder, a shallow step at the front of the housing, so that a sliver of the housed piece's face covers the exposed end grain of the slot, for a tidier appearance where the joint would otherwise show. A plain housing is not, by itself, a strong glued joint: Wearing (2010) noted that a simple or stopped housing relies entirely on end grain gluing, which does not hold particularly well, though the mechanical fit of the joint still stops the housed piece from warping even where the glue bond is weak. Noll (2002) also noted that adding a rebate, a stepped recess along the front edge, alongside a through housing increases the joint's rigidity and cuts down the chance of the whole assembly racking, twisting out of square under load.
Beyond the cabinet
Housing joints appear well outside furniture making. In staircase work, Ellis (1932) described treads offered up and pressed into their housings cut in the string, the sloping board that carries the stairs, with the exact positions of the housings round the newel, the main corner post, marked directly from the parts before the newel is taken down and the housings finally cut, and each riser's width checked by pressing a chisel against the side of its housing. In heavy timber framing the same principle scales up considerably. Benson (1988) described housing the entire end of a beam into a post, rather than only cutting a mortise and tenon into it, to increase the area of wood bearing the load and make the joint stronger against shear and twisting; Sobon (2002) described a related form, the diminished housing, used mainly in an older layout method known as scribe rule framing. On the workshop floor, some housings are no longer cut by hand at all. Frid (1979) described using a dado head, a stack of saw blades and cutters mounted together on a table saw, to cut a housing in one pass, set to the exact width required and lowered to the right depth below the table. Hylton (2005) noted a real limitation of cutting this way: because the cutter is round, stopping a housing partway across the board, for a stopped housing, leaves a curved scoop at the bottom that matches the curve of the blade, rather than a clean square end.