Compared to windows, the main function of doors is to allow free movement through wall openings, and provide basic lockability and security. Windows typically have a sill, and they can start at floor level. In contrast, doors must not have a sill and must start from the floor. Furthermore, even a floor-level opening that is opened with a full sash is considered a door and not a window.
The ways in which doors are opened are even more varied than those of windows. Side hung or double doors have been with us for thousands of years, in all shapes and sizes. Some of the special opening methods worth mentioning include sliding, bifolding sliding doors, swing and revolving doors. As with windows, any combination of glazing, size, and opening method can be use for a door. For example, an asymmetrical double door can have fixed side lighting and top lighting to allow for tilt opening.
1. Traditional wooden doors
Traditionally, wooden doors were made using structural solutions similar to windows. For example, doors utilised flat jamb profiles and block frames (~ rabbated jamb design). Another type of door that was frequently constructed was one using double rabbeted jambs.
Each type allowed for double contact (stop) between the frame and the sash along the side and the header jambs. The continuity of the frame is interrupted at the bottom, in contrast to the design of windows. Here, a frame connector (hidden threshold) hidden by a later floor covering was used to ensure the spacing of the jambs. A threshold was used above it if the door connected rooms with different floor coverings. Traditionally, doors were typically installed together with masonry, with fastening using frame extensions. For partition walls, the fastening could also be provided by connecting to stiffener soft iron wiring.
The flat jamb profile was primarily used for partition walls. Casing could be attached to the jambs on site to cover the joint between the plaster and the frame. In contrast, glued flat jambs were placed so that the glued casing profile aligned flush with the wall plaster. Additional trim casing was also required to conceal the junction between the plaster and the glued profiles.
The rabbeted jamb (block frame) door differs from the previous solutions in that the frame does not cover the entire cross-section of the wall - it is attached to one side of the wall. Such doors were typically built into thicker walls (main walls with or without a recess). The junction between the jamb and the plaster is concealed by a thin casing.
Double rabbeted jamb doors are similar to a glued flat jamb door, but with squarer jambs and thicker casings.
The stile and rail door leaf represents the traditional door leaf type. This is a frame structure consisting of vertical stiles, horizontal rails and solid wood panels or glazed inserts filling the frame. Solid wood panels are joined to the frame elements using groove connections, with surfaces finished with carpentry techniques. Leaves are fixed and opened by hinges, and various locks ensure that they can be properly closed.
2. Modern doors:
a) Outdoor doors (entrance and patio doors):
Modern outdoor wooden doors use a block frame structure, which is not significantly different from window profiles. Frame members are connected by metal or plastic threshold elements that provide thermal-break continuity at the sill.
Door leaves may be modern interpretations of the traditional ‘stile and rail’ system or fully panelled on both faces. Stile and rail infills consist of either 30-45 mm thick multi-layer thermally insulated sandwich structures or thermally-insulated glazing. A combination of these two in any arrangement nominally gives the appearance of stile and rail doors. Double-sided panelled door leaves consist of a wooden frame and inserts made of various materials which have full-surface covering on both sides of the door leaf. The insert for exterior doors is a heat- or sound-insulating material. Door leaves are 50-80 mm thick, but can be 100-110 mm thick where special thermal insulation is required. Covering are either CPL- or HPL-coated laminate, or a veneered execution.
Plastic doors usually have the same profiles and seals as windows. However, due to higher requirements, it may be necessary to use larger cross-sections and even install metal reinforcement cores. The sash, that is the door leaf, is often a stile and rail structure. Inserts are either plastic-coated, thermally insulated sandwich structures, thermally insulated glazing, or some combination of the two.
Steel doors are similar to steel windows - they have a limited role and are more commonly found in industrial buildings. Steel doors constructed from profiles are often installed in partition walls or reveal wall openings. Door leaves are typically panelled on both sides.
Aluminium doors are manufactured with identical profiles as those used for windows. Stile and rail door leaves have frame inserts, which can consist of thermal insulation glazing or a solid, thermally insulated sandwich structure.
b) Interior doors:
Solid wooden interior doors are still being manufactured, albeit in a modern design. These are double-stop block frame or flat jamb doors, made of planed, untreated or surface-treated profiles, which are fitted with modern hardware and sealing. The door leaves can be panelled or ‘stile and rail’ systems.
Contemporary doors with adjustable frames are also widely used. They are considered an improved version of the flat jamb design. Their special feature is a casing that is connected to the jamb core on both sides with a tongue and groove solution. On the opposite side of the door leaf, the casing’s position can be extended by 15-20 mm laterally, allowing the frame to be adjusted precisely to the thickness of the wall. Adjustable frames can span walls up to 20 cm thick, but can also be installed in thicker wall structures (main walls) using additional recessed solutions or the help of additional jack studs.
Another characteristic is that it has no bottom frame: the frame is open. Often, there is no threshold between the door jambs, either. The transition profile and the door leaf position are typically coordinated if the door joins rooms with different coverings.
Adjustable frames are commonly made of MDF boards. Both the frame and the door leaf are available in veneered or laminated finishes. Veneered surfaces must be treated with varnish, glaze, or paint, to protect it. Laminated finishes can be a low-quality decorative foil, a thinner CPL (continuous pressure laminate) coating, or a thicker and more resistant HPL (high-pressure laminate) coating. The infill for veneered or laminated door leaves can be made of solid or hollow particleboard, hollow particleboard ribs or even honeycomb paper grid. The resulting door leaf is 40-60 mm thick.
Numerous accessories are available for doors. These include all the shading devices that we have already discussed in relation to windows: blinds, shutters, fixed grilles, and slats. Other specialised devices related to doors include door closers, bumpers, special locks, panic bars, and door supports.
