Housed joints and wood movement
My workmate, Les, and I have been working on a couple of small contemporary tables. Usually we do our own design work, but this time we opted to use a design for a “floating top” table that has become fairly popular over the last few years. In this design the center stretcher is, in fact, a narrow shelf. We were both surprised that the designer/builder elected to join the shelf to the end stretchers using a “housed” mortise and through tenon type joint. This type of arrangement, with grain direction being perpendicular between the two members, will almost certainly guarantee an “open” joint before too much time has passed.
George Ellis, in his seminal work “Modern Practical Joinery”, defines a housed joint as “Sinking the end of one piece of wood completely into another without reducing it in thickness” (Glossary page 445) Many classic texts on joinery will also characterize a “housed joint” as requiring preparation of only one member of the pieces being joined. By this definition, a dado would be considered a “housed joint”, a sliding dovetail would not. It should also be noted the dadoes were, more often than not, “splay nailed” to prevent them from loosening.
Perhaps the most recognizable “housed” joint is that used in “housed stair stringers”. Anyone who has ever opened up an old, housed staircase is first struck by the fact that both treads and risers are wedged into place. The wedging allows both pieces to be tightly seated into their housings. Housed joints were also commonly used in architectural fitments that were shop built, then assembled on site. And, they were also widely used in furniture construction. However, these would have been structural joints and hidden from view by finish surfaces or mouldings.
The point of this post is not to simply engage in “word play”. It is to caution joinery devotees to make their joint selections based, primarily, on function. Beauty or the high level of skill required to make the appropriate joint should be an “added benefit.” Bird’s Beaks and Wedged Scarfs are both beautiful and challenging to manufacture and, in the right application, are superb in function. Both are generally covered by lead or tile.