Prevent Bay Windows from Sagging

house with bay window
  • 8-20 hours
  • Advanced
  • 400-2,500
What You'll Need
Angular supports
Small cables
Studs or plate

A bay window is a historical design that has stood the test of time. Made famous by medieval and Tudor use of this window pattern in English homes, the bay window crossed the Atlantic and has become a popular feature of American homes. The bay window is specifically designed not to sag, so if you can see a window in a home you are considering buying, or in a home, you rent, then you should first consider whether you are looking at a bay window or a bow window. Assessing your window, and preventing it from sagging, is a quick job that should not take you more than a day.

Assessing the Window

There are 2 different types of windows that project from the house into the street or garden. The most popularly recognized type is the bay window, which is made by extending the foundation, or by cantilevering the joists in the floor so that the bay part can be walked into as though it is part of the floor. Typically, bay windows extend through both floors, from ground floor to roof, and are as unlikely to sag as any other part of the house is. A Bow window, however, is simply a large window which has been curved, and the window sill extended to form a crescent shape. As this is unsupported by the foundations, it may start to sag slightly over time.

Fixing a Sagging Bow Window

A bow window is relatively easily fixed. The sill of the window needs extra support, and anyone with a keen knowledge of home improvement can do this in a day. You can either support the window by adding extra strength supports under the sill, or you can use cables to take some of the weight off of the bottom of the window. The former just requires angular support, available at DIY shops, and a step ladder so you can climb up.

Simply place the support under the window, screw into place, and then caulk around the edges to protect it against water damage. The latter needs some wire cable that is fixed to the outside of the frame and then lifted from the top of the bow window to the roof. The cable is then screwed into a metal plate using a turnbuckle. If your bow window has this already, you should try tightening the cable in order to give the window more support.

Fixing a bay Window

If your sagging window is a bay window, then you will probably need to call in a building inspector, as well as a contractor. Sagging in a bay window involves buckling of the foundations, so it is a serious matter. If rather than the window, you find the floorboards sag in the bay area, then remove all heavy furniture from that part of the room, and have someone replace the sagging boards. This is more likely to be due to water damage than being part of a bay window.