How to Install Bay or Bow Windows

Installing a bay or bow window will bring extra light into a room and give the appearance of more space. The window frame extends past the walls, so the window opening must be braced before you can install your new window. Large bay or bow windows should probably be installed by a professional because they are heavy. These steps will walk you through the process of installing a small to medium bay or bow window.

Difficulty: Moderately Challenging

Instructions

Things You'll Need:

• Tape measure
• 2x4 lumber
• 2x6 lumber
• Plywood panels
• Electric saw
• Bay or bow window with frame
• Metal support braces
• Carpenter's level
• Large clamp
• Screwdriver
• Wood screws
• Fiberglass or foam insulation
• Staple gun
• Roofing paper
• Roof shingles
• Roofer's nails

1. Remove the old window panes and frame from the opening. Use a pry bar to remove the sash stops and tracks from the sides of the window opening.

2. Measure the opening and the bay or bow window's frame. If the bay window is larger than the existing opening, mark the measurements on the outside of the house. Cut through the existing wall studs and drywall to widen the opening.

3. Cut two 2x4s the same length as the vertical studs in the wall. Attach one stud to either side of the window opening so that they touch the ceiling and floor plates. These king studs brace the window opening so it can hold the weight of the bay or bow window frame.

4. Make two header pieces out of 2x6 boards. The headers should be the same width as the window opening. Nail the two headers between the king studs, placing one on top of the other. Check the headers with a level to be sure they are straight.

5. Cut another piece of 2x6 the same width as both headers. This will be the windowsill for your new bay or bow window. Nail the sill between the king studs at the bottom of the window opening.

6. Cut three cripple studs out of 2x4s, making them the distance from the floor plate to the bottom of the windowsill. If you are installing a bay or bow window wider than 5 feet, you may need four or five of to fully support its weight. Install the cripple studs vertically under the windowsill. Nail the two outermost cripple studs onto the king studs that run alongside the window opening.

7. Attach metal support brackets for the bay or bow window. Place them directly over the cripple studs for maximum support. Two brackets will be enough to support a small window, but more brackets may be needed for large windows. Have an assistant help you set the new window frame on the support brackets. Push the frame all the way into the window opening so that it extends past the home's walls.

8. Use a level to make sure the window is sitting straight in the opening. Prop up the lower end with wooden shims if necessary. Clamp the outside of the window frame to hold it to the house temporarily while you install the window panes. Install the glass and check the window with the level again. Once you are sure the window is properly installed, attach it to the house with wood screws.

9. Frame the roof cap with 2x4s cut to fit the window. Place it over the bay or bow window frame and nail it to the house's exterior. Insert fiberglass or foam insulation into the roof cap to prevent heat from seeping into or out of the home through the window. Cover the interior of the roof by nailing plywood to the rafters.

10. Affix a metal drip cap and wooden trim around the outer edge of the roof. Cover the plywood panels by stapling roofing paper on top of them. Attach shingles to the roof cap with roofer's nails, laying them in rows that overlap each other. Seal the point where the roof cap connects to the house with step flashing.