From DIYinfo.org
When you are thinking of buying a new door, take account of the style of your house and the type of doors already fitted, and endeavour to match them. Try not to mix the different door types, as the new one will look out of place among the originals.
If the door is to be fitted at an entrance, where it will be exposed to the weather (and possibly burglars), you must choose an exterior grade door for greater strength and durability. For use inside the house, buy an interior grade door.
Interior grade doors are lighter and cheaper than exterior grade doors, and flush doors are generally cheaper than panelled doors. Some modern doors have a core of compressed fibre board which can be adapted to any style.
When calculating cost remember that doors are not supplied with hinges, locks or bolts. They all have to be bought separately and then fitted. So too do other items of door furniture, such as a knocker, a letterplate, and if appropriate the street number of your house.
Leadlight doors
Doors which include a glass panel brighten up dark hallways. This is why the term light' is applied to a glass panel in, or above a door. Leadlights, once costly because they were hand crafted, are now relatively inexpensive. The light' may be included in the door or as a panel on one or both sides.
Exterior panelled doors
The most expensive types are made of durable hardwood or cedar. They can be coated with exterior grade clear finish to keep the natural appearance. Cheaper exterior doors are made of either good quality timber which may be stained, or lower quality ('paint-grade') timber which must be painted. Some are solid timber, others are laminated and veneered. These are less affected by changes in the weather.
Exterior flush doors
Mostly cheaper than exterior panelled doors. They are faced with exterior quality plywood, but must be painted or stained to give adequate protection from the weather. Some designs have glass pan¬els of various sizes: others are solid.
Interior panelled doors
Top quality hardwood doors may be coated with clear plastic finish to preserve the appearance of the timber. Paint-grade softwood should be painted to ensure that any imperfections are hidden. Interior panelled doors are much cheaper than exterior versions. They are available in many styles - from all wood to practically all glass.
Interior flush doors The cheapest doors of all. Finishes range from plain hardboard to plastic laminate and wood veneer. Some models can be obtained with a glass section.
Moulded doors
This style is made like a flush door, but the facings - usually hard-board or fibreboard - are embossed to look like a panel door. Alternatively, wood mouldings are fixed to the face of the door to give the panelled effect. Moulded doors are usually for interior use only.
Fire-resisting doors
Flats or blocks of units three storeys or more high may require fire-resisting doors. They are usually flush doors with a heavy core of fire-resisting compressed straw or heavy grade chipboard to give either half-hour or one-hour fire resistance. The doors should be fitted in fire-check frames, and an automatic door closer is usually required. A glass panel must be glazed with reinforced wired glass.
Louvre doors
Rows of angled overlapping louvres are fixed between full-length stiles, with top and bottom rails and sometimes a centre rail. Louvre doors are always used inside the house, often on cup¬boards or wardrobes. They may be made from hardwood or soft¬wood. There is a wide range of sizes, including narrow versions for bi-fold or multi-fold doors.
Sliding standard doors
Where there is no room for a hinged door to open properly, the door can be fitted to a track at top and bottom to slide along one wall. Some types of track can be angled so that the,door comes to rest against the frame to give a draught-proof seal when closed. Any standard door can be used. Remember that the wall to one side of the opening must be kept clear.
Sliding patio doors
A glass panel with aluminium edging slides on rollers alongside a fixed panel. The two pan¬els are usually set in a hardwood frame. This style is usually used as a doorway to a garden or patio.
High-security doors
Steel-clad doors can be fitted to the front and back of a house to deter burglars. The doors are made to size to existing frames or to a new frame. The locking action secures the door on all four edges for maximum security.
Slide-in doors
Where space to swing an internal door is limited, a slide-in door or even a double door can be fitted. The slide-in door is supplied complete with frame which is built as part of the wall. For internal use only
French windows
Glazed panel doors which are sold in pairs to open outwards. The edges are rebated to close together in the middle of the opening. They are available with fixed windows of the same height, called sidelights, which are installed on each side of the doors.
Bi-fold doors
Where there is no room for the swing of a conventional door, bi-fold do00rs can be fitted instead. They are like normal doors that have been cut half vertically with the two halves hinged together. They can be fitted singly or in pairs, so that you have four leaves. The doors are usually made wood, wood veneer or steel.
Multi-fold doors
Concertina type doors are excellent space savers and can be used as room dividers. They are hung from a metal track, and some models have a channel set in the floor to guide the bottom edge. The pan¬els may be made of wood, veneered chipboard, plastic, mirrored glass or steel.
Aluminium frame glass doors
Aluminium and glass doors can be fitted at the front or back entrance of a house in a standard wooden frame. The glass is toughened and non see through. The central aluminium rail may contain a letter flap, but doors with a single glass panel taking up the whole area are available.