All About Doors

We probably don’t think much about the doors use every day, but they are among the most complicated components in a house. Particularly with wood doors, high-quality materials and construction are very important for the door to work reliably. Add in the variety of styles used in door construction and it becomes clear there is more to them than meets the eye.

One thing common to all doors is sizing. The standard height is 80 inches. Standard widths are in 2-inch increments. Exterior doors usually come in 30-inch, 32-inch, and 36-inch widths. Interior doors start at 12 inches and run up to 36 inches. Doors wider than that are either custom-made or a combination of two doors.

Carpenters and suppliers often use feet and inches, rather than just inches, to describe door size. For example, a 32-inch by 80-inch door would be 2-8 by 6-8.

Exterior Doors are Thicker, Stronger, and More Weather-Resistant

The first distinction between doors is whether they’re for interior use or exterior. Exterior doors have to be more rugged than interior ones, both to offer security and to keep out the weather. For security, exterior doors are thicker than interior ones, usually measuring 1 ¾ inches. The also have weatherstripping and special sills designed to keep out rain and wind.

Wood is the traditional material for exterior doors and it’s still commonly used. The glue used to build exterior doors is waterproof. Even so, maintaining the finish on wood doors is critical both for durability and to keep them from warping. Many exterior doors today have a wooden interior frame that’s faced or “skinned” with galvanized steel or fiberglass. The space between the skins is filled with rigid foam, providing better insulation than a wood door. These are made to resemble traditional door styles, while costing less and requiring less maintenance than a wood door.

Often, exterior doors are flanked by sidelights, which are smaller, stationary door panels with glass “lights”, or windows in them. All glass used in or near any door is required by code to be safety glass to minimize the risk of injury should the glass break.

Most exterior doors are hinged (Higher quality, heavier doors use ball-bearing hinges for easier opening), but doors used for secondary access such as to a patio may be sliders.

Interior Doors Come in a Wide Variety of Styles

Doors for inside the house are usually thinner than exterior doors, with the standard being 1 3/8 inches. A lot of interior doors are made entirely from wood, with pine being the most used species, and poplar and alder close behind. These three species are generally intended to painted. A variety of hardwood species are available as well for stain-grade work, but expect to pay more.

In addition to solid wood, interior doors are frequently made “hollow core.” Hollow core is a bit of a misnomer, though. There will be a wood or MDF frame around the perimeter of a hollow-core door, and the space in the center will be filled with a lightweight but surprisingly strong cardboard honeycomb.

The skins of these doors can be thin, hardwood plywood or MDF for flat, or “flush”, doors, or an engineered wood product such as Masonite and MDF that’s molded into a traditional paneled design. Such doors can also be purchased as “solid core”, where the center is filled with particle board. They are much heavier, and feel more like a solid wood door.

Door Styles Typically Feature Frame-and-Panel Designs

Traditionally styled doors have either four or six panels. The vertical members separating them (and on which the hinges and lock are mounted) are called stiles. The horizontal members joining the stiles are called rails. The reason for this construction has to do with the way that solid wood expands and contracts with changes in humidity.

A door built of planks joined edge to edge might grow and shrink half an inch or more over a year, making it too tight or too loose in the jamb. The panels in a traditional frame-and-panel door fit loosely in grooves, or “dadoes” in the rails and stiles, and they’re free to expand and contract seasonally without changing the door’s width. The only seasonal wood movement that can affect the width is in the stiles, and that’s much less than if the whole door could grow and shrink.

Most door styles are a variation of paneled doors. Instead of a panel, a door can have louvres for ventilation or glass for light. The glass can be clear or frosted in some way for privacy.

Door-Hanging Details Ensure Smooth, Secure Operation

Doors hang from jambs (from the French word for “leg”). In most cases, the door is hinged to the jamb, and “stop” molding is applied to the jamb faces to stop the door from swinging in too far. Lightweight doors can hang from two hinges, but three hinges are always preferred to better align the door and the jamb. Hinged doors are said to be “handed”, referring to which side the lock (or the hinges) are on. There is no industry standard for handing, so be sure to understand your supplier’s nomenclature when ordering doors.

Doors can be purchased as just the door, or “slab.” But these days, it’s more common for builders and remodelers to order “pre-hung” doors already hinged to the jamb and bored for a lock.

Most doors are single, that is, just one door in the jamb. Wider openings will use two doors in a jamb. Double doors on closets are often “sliders”, where the doors hang from a track above and slide open and closed. Pocket doors are also sliders, but they can be single or double, and they recess into a cavity in the wall when open. Recently popular are “barn doors”, where the door slides on a decorative track in front of the wall.

They can also be “twins” where each door is hinged on an opposite jamb leg. Twin doors for closets are usually held closed with magnet catches. Twin doors in traffic areas will have a “passive” side held closed with slide bolts, while the “active” side operates with a normal lock whose latch engages in an “astragal” applied to the edge of the passive door.

Finally, there are bifold doors. These are like twins in that they’re hinged on each side of the opening. But each side of a bifold door is composed of two smaller doors hinged to each other – essentially, a twin with four doors. When you open one side of a bifold, its two doors hinge in the middle at the same time the jamb-side door hinges there. The two inner doors in a bifold are guided through this motion with a pin in their top that rides in a track screwed to the jamb head. Bifolds are held closed by spring tension.