What distinguishes custom wood doors from mass manufactured wood doors? The mere creation of wood doors to match a given size is no guarantee of the quality expected of custom wood doors. Manufacturing technologies have been developed so that it is simple to manufacture a door to many different sizes, by the thousands, with little quality built in. Traditional techniques of building a true custom door yield a quality that is not replicated by todays' mass manufacturers.

The highest and best door joinery techniques were largely developed by the time of the Egyptian pharoahs, and have evolved little since then. The custom wood door is distinguished by mortise and tenon construction, where the horizontal rails of a door are the same width as the door (or just an inch or so less), and the rails have tongues, or "tenons" which project beyond the vertical members', or stiles' edges into a mortise, or rectangular hole. These tenons are then pinned in the mortises by dowels, which anchor the mortises and the tenons together even if the glue in the joinery fails as it eventually will.

Up until the advent of the industrial age, the quickest way to assemble a door was to use mortise and tenon construction. Since the advent of water or electric powered factories, drilling has become more expedient, and it is cheaper to attach rails and stiles with round wooden pegs, glued into both the stiles and the rails. The rub with this technology dear to mass door manufacturers, is that the dowels are only glued to each side, with comparatively little surface area. When the wood shrinks and the glue fails as always happens, the joint loosens up and the door falls apart. Later improvements in manufacturing technology have allowed the substitution of solid wood with composite materials, fabricated of saw dust or wood chips and glue. The only reason the saw dust or chips are in the composite, is that the saw dust or chips are cheaper than the glue.

Custom wood doors have other distinguishing features that manufactured doors do not, beside mortise and tenon joinery. Such doors are often embellished with moldings to match a particular profile, or hand carvings, or custom cast or machined hardware. Various landmark preservation organizations often require that doors for historic buildings match the original doors, in profile, section, joinery and elevation. The hardware of the doors may be replicated using the lost wax or sand casting and chasing processes to replicate an original design, that is not otherwise available today.

Another distinguishing factor of a custom door (mortise and tenon joinery) is that it has a lifetime measured in centuries, not decades. With proper maintenance as hinges wear or finishes deteriorate, a custom made door made of a naturally durable wood commonly including walnut, cherry, Honduran mahogany, teak, white oak, and Spanish cedar, should last centuries, even in active service. Pine used to be a durable wood, but grows too fast in the latter half of the twentieth century due to global warming, to have developed the resins necessary to impart natural decay or rot resistance to stand up to long-term service.

Most importantly, the beauty of a fine custom made doors will be appreciated for lifetimes, and improves with age. Those fortunate enough to have appreciated fine centuries' old doors cherish their memories of them, as the flotsam and jetsam of manufactured doors recedes quickly.