Window sills serve an important function in the construction of buildings, helping to keep water from home interiors when window fittings shift and settle. Constructing effective window sills helps to preserve structural materials of the home. Window and window sills are installed at a standard height generally accepted by most contractors, unless other design considerations come into play.
Window Sill Materials
Traditionally, window sills were made of wood, stone, granite, brick or other locally available materials that made their construction convenient and inexpensive. Window sill materials generally echoed the construction of the rest of the structure. Wood is the most common material found in residences throughout the United States. Unfortunately, wood sills are vulnerable to water intrusion and condensation from windows. Rotting can occur and progress to an extent that requires replacement of the entire sill. Because of this disadvantage, other materials became widely used. Marble and granite window sills are frequently found in today's home construction. These materials withstand the elements better than wood and provide a high-quality sill surface that is attractive and durable.
Constructing Window Sills
Windows can be constructed to any height, and window sills by their nature must follow the proportion of the windows. Windows set at standard height in high-ceilinged rooms would leave too much wall area at the top of windows that would be disproportional to the rest of the room. Adjusting the height of the windows and their sills to fit these taller home designs is necessary to retain the visual scale of the room.
Standard Height of Window Sills
Windows are generally constructed 3 feet above the floor. The windows are installed at the bottom of the windows. The sills are often attached to 2- by 4-inch blocks that are inserted between the drywall and the wall studs so that there is plenty of mounting material to hold the sills. The sills are drilled and set into place, then all seams are caulked to make them waterproof. If sills are to be painted, the nail heads are filled with putty and allowed to dry before priming and painting with a topcoat.
Non-Standard Sill Heights
Windows and sills may be positioned differently to suit both ceiling height and other design considerations, such as natural light, unusual window shapes and built-in structures near the windows. Windows facing east and west receive the low angle of sunlight in the spring and fall which can be blinding to occupants of the structure. Raising the sill height to 4 feet off the floor helps to reduce this glare, according to writer and general contractor Duo Dickinson of the ThisOldHouse website.