Entry and exterior solid wooden door can be a key focal point of a house. Unfortunately, because they are exposed to weather and heavy wear, these doors often show their age prematurely. Most older doors are made from wood, a material that has the warm, natural look and feel that many people prefer but is vulnerable to the elements.

Season after season of sun and rain eventually warp, crack, and bow wood, as the sun’s ultraviolet rays break down wood’s natural lignin, and moisture repeatedly shrinks and swells wood fibers. As a result, given enough time, wood doors give up the ghost.

Luckily, entry and exterior doors have changed significantly over the past few years. Homeowners may now select from a wonderful smorgasbord of options. Hundreds of types and sizes are available, from conventional wood models to high-tech alternatives made of fiberglass composites and steel.

One significant change with entry doors is that, unless you’re looking for a bare-bones door replacement, you can now buy an entire “entry system.” With an entry system, a door is pre-hung in its frame, the door’s bottom edge interlocks with the threshold, and weather stripping encircles the door’s perimeter. The hinges and lockset are designed as part of the system, and sidelites often flank the door. With a system, all components are designed and machined to work together reliably and with energy efficiency.

Another change in the door industry is that the lines that once distinguished one door-building material from another have blurred. A wood door isn’t necessarily entirely wood anymore. In fact, some wood doors have steel interiors, and steel doors have wood exteriors. A fiberglass or steel door may have a wood frame. And nearly any door may have a core of foam insulation.

Even so, for the sake of discussion, it helps to consider doors according to their primary face material. The choice of wood, fiberglass, or steel as a surface material has the greatest impact on a door’s appearance, cost, durability, and security.

Nearly all doors, wood and non-wood alike, are termed either “flush” or “paneled.” Flush wood door are flat and smooth on both faces. Paneled doors have rectangular recesses framed by horizontal rails and vertical stiles. Panel construction originated with wood doors to minimize cracking and warping by giving panels enough room to shift as they expand and contract with changes in humidity. Doors with doorlites have panel construction with one or more lites substituting for a panel or panels.

A terrace or patio door is hinged and has glass lites. Hinged glass-lite doors mounted in pairs that swing independently are called French doors.

Exterior sliders have one fixed panel and one panel that glides along top and bottom tracks. These doors operate easily, seal out the weather well, and admit plenty of light.

A door that opens toward you and has its knob on the left side is a left-hand door. A door that opens toward you and has its knob on the right side is a right-hand door.