How to Install Dormer Windows

Updated February 21, 2017

Dormers that are installed on the roof of a home can be a solid structure, or they can be used to create extra space in a small area in an attic or second floor. Installing a dormer window adds to the aesthetic appeal of the home and adds light to a dark area. You can install dormer window by first determining what type of window that you want to use.

Measure the width and height of the opening for the window with the tape measure. Make a note of the measurements on a piece of paper.

Purchase a window for the dormer at a home improvement store that matches the measurements that you took in step 1.

Check the new window and make sure the fins around the exterior of the window are straight and not bent.

Apply a bead of caulk on the back side of the fin around the perimeter of the window.

Place the window into the frame by setting the bottom into the opening first and then tilting it up.

Drive a nail part way into each corner of the fin to tack it into place. Do not drive the nails all the way into the wood frame.

Place a level on the top, bottom and both sides of the window. You are checking to make sure that it is level and plumb.

Measure diagonally from the top corner to the bottom corner on each side of the window with the tape measure. If the measurements are within 1/16 inch the window is sitting square in the opening.

Drive nails around the perimeter of the fin to secure the window to the dormer.

Apply trim around the window to complete the installation. Measure and cut the trim to the width and length of the window with the circular saw. Set the trim in place around the window and secure it with the nail gun.


Level is indicated when the bubble is in between the parallel lines. New windows come in a single piece that is a standard size or can be custom made to the size of the window opening.

Things You'll Need

  • Tape measure
  • Paper and pencil
  • Caulk
  • Level
  • Trim
  • Circular saw
  • Nail gun
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About the Author

Cameron Easey has over 15 years customer service experience, with eight of those years in the insurance industry. He has earned various designations from organizations like the Insurance Institute of America and LOMA. Easey earned his Bachelor of Arts degree in political science and history from Western Michigan University.