How to Mull Vinyl Replacement Windows Together

Alexander Callos

Mulling two windows together can give a house a completely new and improved look. A mullion is a structural element which divides adjacent window units. Larger windows generally improve the appearance and quality of a home. Mulling is one way to get larger windows.

Mulled windows are two smaller windows in one, bringing both beauty and elegance. Mulling these windows can be a bit of a challenge, and even experienced homeowners may have trouble with this project.

  1. Measure the height of the two windows that will be mulled together. Record the measurement. Measure the same height and mark on the mullion piece. Cut the mullion piece with a utility knife so it is the exact height as the two windows being mulled together.

  2. Apply a bead of caulk inside all four corners of the mullion. Run the caulk from one end to the other and repeat the process for each side of the mullion piece.

  3. Put the mullion piece on one of the windows. Press down and hold firmly to allow the caulk time to adhere to the window. Set the other window in the other side of the mullion piece. Hold firmly in place just like the first window so it can properly adhere to the mullion.

  4. Slide open the top sash of each window and drill three screws evenly spaced into the top balance track of each window. Insert one flathead screw directly into the center of the frame in the lower sash balance track for both windows.

  5. Pull open the lower sash and drill a flathead screw in at an angle into the mullion piece and below the sill in the balance track. Repeat this process for the other side.

  6. Shut the top sash and insert a flathead screw under the it in the center of the frame on the balance track and another behind the sash stop for the upper sash in the balance track.

  7. Check the windows to ensure no screws are interfering with the sashes. Caulk where the windows meet at the top if there is a gap. Allow the caulk time to dry before installing the window.