DJ Delorie replies: Since wood expands and contracts mostly across its grain, a rail and stile frame produces a door with a more consistent size, so you don’t have large variations in gaps (or doors sticking) due to changes in humidity. The panels still expand and contract, but there’s usually some space inside the grooves to allow expansion without damaging the door. Look for a product called “spaceballs” that you can put in this extra space to gently hold the panel in place.
Note that it is possible to build a solid panel door. You must use the same care that you’d use for a solid table top, and account for the expansion and contraction in your design. For example, solid panels are probably best when the door is in front of the face frame, with a large space between it and the next door, so that changes in width will be far less noticable.
In any case, keep track of the ambient humidity when you build these doors, so you know whether the door, as built, is near its largest or smallest size so you can plan accordingly.
Roy Noyes replies: There are a number of good reasons for using frame and panel construction instead of solid. First and most important is it’s relatively small change in width due to changes in humidity. A 24˝ wide solid eastern white pine door will expand and contract about 5/16˝ as the equilibrium moisture content goes from 6% to 12%.
The same door in frame and panel construction with 3˝ stiles will expand and contract only about 5/64˝ — one fourth as much! This is especially important for doors in places like New England where our houses are very hot and dry in the winter and hot and humid in the summer. Note that doors with quarter-sawn stiles will shrink and swell only about half as much as doors with flat sawn stiles, or about 1/32˝ for the above door.
For more on the dimensional change in wood with moisture content see Understanding Wood — R. Bruce Hoadley, The Taunton Press.
Also, consider aesthetics. A frame and panel door has a light and friendly feeling, while a solid wood door feels massive and forbidding. Frame and panel can also be made more decorative with raised and/or arched panels with numerous shapes on the edges, while solid wood doors can be enhanced only by carving, decorative hinges or selection of striking wood grain patterns.
Solid wood doors are easier and quicker to construct, however they also tend to warp and twist as the wood expands and contracts.
Obviously, there are places that are suitable for both kinds of doors, but which one you choose should be selected after careful consideration of all these factors.