When to Install a Windowsill in Concrete

Windowsills

• A windowsill functions as both part of a window and part of a building's frame. Sills comprise one part of the barrier between a window and a home frame and help adhere the window to the building. Windowsills also serve as the primary means of protection against water by directing it out and away from the home. This function protects both the window and the frame of a building against moisture damage. Broadly speaking, every window needs a sill.

Installing Windows in Concrete

• You must create a barrier between a wall and a window in concrete. This barrier helps adhere the window to the wall. Barriers, or frames, into which windows are placed contain four parts: a top, two sides and a bottom. The bottom part of the barrier generally serves as the windowsill. Therefore, technically speaking, any time you install a window in concrete, you also install a windowsill. Extending the bottom part of the barrier well beyond the window and adding slope to it help ensure the water rolls away from the window and off the sill.

Concrete Windowsills

• You can install numerous types of windowsills, including concrete. The type of windowsill you install depends upon both aesthetic and practical considerations. Concrete windowsills provide greater strength than wood, plastic or vinyl sills. As a building material, concrete also exhibits a greater degree of moisture-, fire- and insect-resistance than wood. However, concrete generally provides poor insulation. In cold areas, concrete windowsills may add to heat loss. Aesthetically, concrete windowsills blend well with concrete walls, and builders can customize colors upon request to match them with the exterior or interior decor.

Additional Considerations

• Some windows may come with their own sills, or other components, such as long, sloping handles designed to serve the same function as sills. You can install these windows in concrete without adding a windowsill, though a windowsill can provide additional protection against moisture penetration. In fact, there is no real reason not to install a windowsill. Because you must build a barrier, or frame, and a windowsill can serve as part of the barrier, installing one requires little extra work, and it always provides increased protection to your home and windows. A sill pan -- installed at the base of the window along with the sill -- provides extra protection to your window.