A banister is a rail that runs along a staircase. It functions in two primary ways: to give people walking up and down the staircase a railing to hold onto and gain balance from and to keep people from toppling off the side of the staircase on to the floor below. Even staircases that have walls on either side of them, such as stairs that lead up into an attic or down into a basement, are often built with a banister just to give the people walking up and down the stairs a railing for balance.
There are many different banister designs and there are a few kinds of products that are used to make banisters. Most commonly banisters are made out of metal or wood. In some cases, with banisters that are built along with exterior staircases, concrete or stone is used as the key building material for the banister. In a few cases, in buildings that are designed on a grand scale, a banister made out of one of these kinds of materials will appear inside of a building. This is usually only done for large, central staircases.
A wooden banister is usually slatted rather than solid. There are one or more slats on each stair level and their number and spacing depends on their width. Thin slats or posts are usually positioned closely together. Wide slats are positioned a bit farther apart. One of the key functions of the slats of a banister is to provide protection that keeps objects from falling off of the stairs. They are also important to keep small children from falling and are usually spaced so that even a very small child could not fit between then.
In addition to being used on stairs, banisters are sometimes used in an upper hallway or room that looks down over a room on the lower level. Here, the key purpose of the banister is safety rather than balance. These kinds of banisters are used both internally and externally. For example, a deck that is elevated even just a few feet off of the ground will be designed with a banister that rings the entire exterior area except for the side or sides of the deck that are attached to the adjoining house or building. For decks that are one or more stories above the ground, it is especially important to install sturdy banisters.