How to Make an Exterior Door Threshold

Measure the new threshold's width and transfer this measurement to a piece of 1/4-inch hardboard. Use a level as a straight edge to draw a line down the hardboard. Rip the hardboard along the line with a circular saw. Cut the hardboard strip short enough to easily fit in the door opening.

Butt one end of the hardboard strip against one side of the door jamb. Open a scribes to the thickest gap between the hardboard strip and the jamb. Trace the scribes down the hardboard, following the jamb's contours.

Cut the hardboard template along the scribe lines with a jigsaw. Test fit the template against the door jamb. If it does not fit tight against the jamb, determine which area is hitting the jamb and use a rasp file to sand it down. Then test fit again. Continue to sand and test fit until the template fits tightly against the jamb, with no gaps.

Measure the door opening's width at the widest point and add 1/16 inch. Transfer this measurement to the new door threshold. Cut the threshold to the appropriate length using a circular saw.

Flip the threshold upside down and lay the template on the underside. Make sure the template is positioned on the threshold the correct way, since each side should be a mirror image of the other. Trace along the template with a sharp pencil. Flip the template over to the other side and repeat this step.

Cut along the tracing, on both sides of the threshold, with a jigsaw. Use a rasp to clean up the edges and make the contour's bends as square as possible.

Test fit the threshold in the door opening. Make any necessary minor adjustments with the rasp until the threshold fits easily in the opening with no gaps on either side.