How to Install a Bay Window

Two Methods:Preparing a Stud-Frame Wall for Installation

Bay windows can let in more light and provide seating space in a room. How you prepare to put in a bay window can depend on your walls' construction material. Follow these steps to install a bay window.


  1. 1
    Check the bay window for any damage and that any working windows are closed and locked before installing it.
  2. 2
    Measure the width and height of the window's rough opening in the wall. Each dimension should be about 1/2 an inch (1.25 cm) larger than the bay window's width and height. Use a level and measuring tape to determine that the rough opening is square and even.
  3. 3
    Apply sealant to any joint larger than 1/16-inch (0.15 cm) in the wood framing attached to the masonry or between the wood and the masonry.
  4. 4
    Brush liquid applied flashing over the wood framing and surrounding masonry where the window's jambs and head will be.
  5. 5
    Place shims along the sill and underneath mull joints as specified by the window's manufacturer. Secure them with sealant.

Method 1
Preparing a Stud-Frame Wall for Installation

  1. 1
    Remove enough siding from the wall around the rough opening to reveal the building wrap underneath. Uninstall any existing window from the wall.
  2. 2
    Make sure the studs and header around the rough opening are safe and can support the bay window. Prepare the sill for the bay window as directed by the window's manufacturer, such as by adding a drain mat.

Method 2

  1. 1
    Drill evenly spaced pilot holes around the bay window's inside perimeter. Countersink the holes.
  2. 2
    Work with at least 1 other person to install the window. Place the bay window onto the prepared sill in the rough opening. The opening's framing should fully support the windowsill.
  3. 3
    Hammer a galvanized roofing nail into a lower corner of the window's nailing fin to hold it in place.
  4. 4
    Line up side jamb shims with the pilot holes to allow fasteners to penetrate the shims. Use sealant to secure the shims.
  5. 5
    Check the bay window to make sure it is level, plumb and square. Test that the window operates correctly.
  6. 6
    Fasten the bay window's jambs, head and seat board by drilling pan head screws into the pilot holes. The screws should go through the installed shims.
  7. 7
    Apply flashing to a stud-frame wall.
    • Spray adhesive on the sides and head of the window's nailing fin, building wrap and sheathing.
    • Apply self-adhesive flashing on the stud-frame wall around the bay window. Use a J-roller to press the flashing down. Readjust the flashing if necessary so it is free of gaps or bubbles.
  8. 8
    Use a cable system or seat board bracing to permanently support the bay window's weight. The support system should be able to handle at least 750 lbs. (340.2 kg) to include additional weight on the window from people or household items.
  9. 9
    Seal the window's 4 corners with a 1/4 inch (0.63 cm) layer of sealant. Add low

expansion polyurethane foam to create a continuous air seal between the interior window frame and the rough opening for a bay window installed into a stud-frame wall.


  • Hire a contractor who has actually installed bay windows to ensure things go smoothly.
  • It is best to have a professional put in a bay window in an upper-story floor.
  • If installing a bay window under an eave, measure the depth of the eave horizontally before choosing the window. Pick a bay window that is shallow enough to fit under the eave.


  • A small roof, or skirt, must be built over any bay window that has no overhang right above it or extends beyond its sheltering eave.

Things You'll Need

  • Bay window
  • Measuring tape
  • Level
  • Sealant
  • Liquid applied flashing
  • Utility knife
  • Drain mat
  • J-roller
  • Caulking gun
  • Construction stapler and staples
  • Drill with bit and countersink
  • Hammer
  • Roofing nails
  • Pan head screws
  • Spray adhesive
  • Flashing
  • Low expansion polyurethane foam

Article Info

Categories: Doors and Windows