Building an insulated door for your home or garage can be a fairly complex DIY project. You’ll definitely want to follow the “measure twice, cut once” philosophy when you learn how to build an insulated exterior door. Mistakes will result in the door not fitting well in the opening and can cause some serious issues that will be difficult to correct. In order to save some time, consider reaching out to the home improvement experts at PJ Fitzpatrick. We’ve been installing new exterior doors for homeowners throughout the Delaware Valley since 1980.

How to Build an Insulated Exterior Door Step by Step

1. Set one sheet of OSB on a level floor to create your work surface.
2. Measure and cut underlayment sheets to produce two pieces that fit your door opening. Common door sizes are 32×80 or 36×80 inches.
3. Set one door-sized piece of underlayment on the OSB work surface.
4. Cut one piece of 1×4 lumber to the length of the door.
5. Cut the 1×2 lumber to produce one length of the door and two pieces the width of the door between the vertical pieces.
6. Glue the lumber pieces to the edges of the underlayment piece. Use the 1×4 piece for the hinge side of the frame.
7. Clamp the pieces in place against the underlayment piece and let glue cure.
8. Cut a piece of rigid foam insulation to fit inside the frame of the door.
9. Take off clamps, spread glue throughout the interior of the door frame, and press the insulation into place.
10. Set some weights on the insulation to keep it firmly flat against the door while the glue dries.
11. Distribute glue across the insulation and door frame.
12. Place the second sheet of underlayment against the glue to form the final layer of the door.
13. Align the second sheet carefully so that it is flush with all edges.
14. Secure the corners of the layers with 1-inch wood screws.
15. Use a power stapler to attach the top layer all around the edges.
16. Set the second sheet of OSB over the door.
17. Drive the longer wood screws through the corners of the OSB sheets only. You want the screws to connect the top sheet to the bottom sheet without penetrating the door. This creates pressure to squeeze the new door flat while all of the glue dries.
18. Release the OSB sheets and cut a doorknob hole with a hole saw.