A comprehensive guide on what you need to know before choosing the right “interior door".

To separate living areas and spaces, interior doors close off the view and sound from one area into the next. Interior doors often go unnoticed, but the design can enhance the living space. Sound transmission (STC) is an important factor in choosing an interior door. While not considered for closet doors, STC ratings on interior doors sectioning off one room from another should be considered. Theater rooms are designed as sound-proof, with an STC of 60 but most rooms in a home do not require that level of noise blocking and STC 40 will soften or deaden the sounds from most conversations.  An STC of 25 permits hearing normal conversations.

Solid Wood: Generally solid wood interior doors are six panel pine, but interior wood doors can be constructed from softwoods and/or hardwoods, such as mahogany, cherry, alder, maple, oak and pine. Solid wood doors must be maintained — stained or painted — on all surfaces as they will shrink and expand with changing humidity levels and temperatures in a building. With an STC of 35 to 40, solid wood doors will block most conversation sound transmission unless designed with glass inserts.

Medium Density Fiberboard: MDF is an engineered product of recycled wood fiber mixed with a resin and formed or molded into products, such as interior doors. The material is extremely stable and will not warp or shrink with changing temperatures or humidity levels. MDF does not have a grain and is easy to paint. Because doors are solid, MDF provides a similar weight to solid wood and STC levels of 32-35 (check with individual manufacturers).

Hollow Core: Constructed with a plywood or molded composite skin, these doors are hollow so sound and temperatures easily pass through. STC ratings vary but register as low as 20.

Solid Core: Constructed with a plywood or molded composite skin, these doors are filled between the skins with a wood fiber blend. STC ratings about 25-26 depending upon the filler blend.

Metal and Glass: In modern and contemporary homes, metal and glass doors are being used to accent the building’s style. Glass doors or inserts do not provide privacy, but when closing off heavy traffic areas or closets, they add character to the space. Steel doors, frequently used in commercial or industrial buildings, have high STC ratings of over 50.

Panel Doors are the most commonly used interior doors. Created of solid wood or MDF the basic design has stiles, rails and six panels. Many manufacturers now create panel doors in a variety of designs, from two panels to five and six panels, with clear glass or translucent glass inserts. Solid panel doors are hinged and swing in or out, most frequently closing off bedrooms from the traffic areas of a home or in an office situation. Panel doors with glass panels may be used on closets or in traffic areas where privacy is not an issue.

Flush Doors are made of MDF or plywood as hollow core or solid core with a smooth skin; no stile, rail or panel design and are used in modern architecture.

Sliding Doors, constructed of wood, glass in metal, or mirror over wood or metal, travel along a railing. They do not impede traffic areas as they ride flush against a wall or closet.

Pocket Doors, most frequently found in older homes, slip between the walls of a room and the next room, saving space. When opened, they are not seen.

Folding Doors are usually found in small spaces as the door panels fold against each other. Used for closets, pantries, storage or laundry areas. Folding doors can be less wide panel doors or louver doors, which offer ventilation since the slats of the louver design are angled with air spaces between. Louver doors also can be hinged.

French Doors are named for two hinged panel doors, usually with glass panels, that meet in the center so they swing in or out together.  Used in areas where light is to be brought into the room or for a view, French Doors are often seen connecting two rooms or a living area to a balcony, patio or deck.

Barn Doors now are used inside. Providing a design aesthetic, Barn Doors also save space as they hang from a rail and slide against the wall when open, covering the opening when closed. Space saving, they also become a feature of the space.

Hinges, knobs and/or levers come in myriad designs and materials. When choosing an interior door, match the style of doorknob to the door design. Levers should be used for contemporary or modern design, when aging-in-place is an issue, or for French Doors, where a push/pull function is needed. 

Material: Solid Wood doors cost more, especially if exotic woods are chosen.  Metal and Glass doors also can be more expensive than MDF, hollow core or solid core due to the later three being constructed of less expensive materials.

Style: A flat panel MDF or hollow core door are affordable and appropriate for use in most homes. Panel doors of wood will increase the price while French Doors will be more expensive since two doors are required to create the design.

Glazing: Adding decorative glass panels to an interior door will raise the cost.

Hardware: Simple nickel or brass door knobs and hinges are the least expensive. Nickel or brass lever style door handles also are not costly. If a special metal such as bronze is desired to meet a specific décor, the prices will increase.