Among the architectural arrangements of an edifice, the door is by no means the least in importance; and if properly constructed, it is not only an article of use, but also of ornament, adding materially to the regularity and elegance of the apartments. The dimensions and style of finish of a door should be in accordance with the size and style of the building, or the apartment for which it is designed. As regards the utility of doors, the principal door to a public building should be of sufficient width to admit of a free passage for a crowd of people; while that of a private apartment will be wide enough if it permit one person to pass without being incommoded. Experience has determined that the least width allowable for this is 2 feet 8 inches; although doors leading to inferior and unimportant rooms may, if circumstances require it, be as narrow as 2 feet 6 inches; and doors for closets, where an entrance is seldom required, may be but 2 feet wide. The width of the principal door to a public building may be from 6 to 12 feet, according to the size of the building; and the width of doors for a dwelling may be from 2 feet 8 inches to 3 feet 6 inches. If the importance of an apartment in a dwelling be such as to require a door of greater width than 3 feet 6 inches, the opening should be closed with two doors, or a door in two folds; generally, in such cases, where the opening is from 5 to 8 feet, folding or sliding doors are adopted. As to the height of a door, it should in no case be less than about 6 feet 3 inches; and generally not less than 6 feet 8 inches.
299. - The Proportion between Width and Height: of single doors, for a dwelling, should be as 2 is to 5; and, for entrance-doors to public buildings, as 1 is to 2. If the width is given and the height required of a door for a dwelling, multiply the width by 5, and divide the product by 2; but if the height is given and the width required, divide by 5 and multiply by 2. Where two or more doors of different widths show in the same room, it is well to proportion the dimensions of the more important by the above rule, and make the narrower doors of the same height as the wider ones; as all the doors in a suit of apartments, except the folding or sliding doors, have the best appearance when of one height. The proportions for folding or sliding doors should be such that the width may be equal to 4/5 of the height; yet this rule needs some qualification; for if the width of the opening be greater than one half the width of the room, there will not be a sufficient space left for opening the doors; also, the height should be about one tenth greater than that of the adjacent single doors.