Adding a bay window to your living room not only can make the room appear larger, but it can bring in extra light and enhance the room. But adding a bay window can be challenging, since the window itself sticks out from the home's wall. You can't just add the window without factoring in extra structural framing as well as a roof above the window.
Establish on which wall in your living room the bay window will be installed. If there's an existing window, you need to remove it, starting with the sash stops that hold the window in place. Pull the stops free from the sides and then from the top. Pry loose the sash tracks, removing both the sash and tracks. Remove storm windows.
Measure the bay window, and mark the measurements on the outside of the house. Cut along the window frame if need be. Frame the new window by cutting through old studs.
Attach support braces to the rough sill, and add cripple studs to match the support braces. Lift the bay window onto the support braces, sliding it into the rough opening of your living room. Make sure that there is a stable, level surface to place the bay window upon.
Check to make sure the bay window frame is level. You may need to use shims if it's not level. Use screws to temporarily keep the frame in place and a cable clamp on the outside to hold that part in place. Secure the center window and snap the other windows into place. Drive screws into the frame once you again check to see if everything is level.
Frame the roof cap, and secure it into place above the window bay. Fill the interior space with fiberglass insulation. Nail plywood decking to the rafters once the insulation is added.
Apply wood trim to the perimeter of the roof, along with a metal drip cap. Lay roofing paper over the plywood, and staple it into place. Attach shingles to the roof. The second row, and each subsequent row, should overlap the row before it. Install step flashing to prevent leaks where the roof cap connects to the wall.
Keep in mind that a south-facing bay window lets in the most light, while the north-facing window gets the least amount. One facing east collects morning sun, while one facing west receives evening sun. Many home-improvement stores can assist you in answering any bay-window installation questions. You should have someone around to help you with this project, as you may need an extra set of hands for some of these steps.
Don't use the bay window cut out as a window seat. If you want to sit by the window, you need to frame out a walk-out bay, which is more work. This is a project you don't necessarily need to do while initially installing your bay window.