Bay Windows

Bay windows are the most expensive residential window style, because the price covers far more than glass: three units, a seat board, a head board, a roof, flashing, insulation, and structural support. The Norden Seal installed cost ranges by size are listed in the table on this page. Expect a bay to cost several times a single casement of equivalent width.

Yes. A bay projects out from the wall, so its weight has to be carried either by cable supports anchored into the header above or by knee brackets underneath. On a replacement, an existing bay usually has that support in place. On a new bay cut into a flat wall, a structural header is required and the work needs a permit.

Often, yes. If the seat board, head board, roof and supports are sound, the three window units can be replaced within the existing bay structure. If the seat board is soft or the roof has leaked, the assembly should come out entirely. A dropped or rotted seat board is the most common reason an old bay needs full replacement.

They can be, and it is almost always the seat board and head board rather than the glass. Those flat surfaces connect directly to the outside and are frequently under-insulated on older bays. A properly built bay has a fully insulated seat and head cavity and a warm-edge glass package, and performs as well as the wall around it.

Most residential bay windows project 16 to 24 inches from the wall, which gives a seat board deep enough to sit on with cushions. A 45 degree bay projects deeper on the same wall width than a 30 degree bay. If the seat is the point of the project, specify the angle up front, because it changes the framing.

A bay window uses three units set at angles, with a defined faceted shape. A bow window uses four to six units set at shallower angles to form a gentle curve. A bay projects further on a narrower wall, while a bow spans wider and projects less. Bays cost less and give a deeper seat.