Garage doors are much better at insulating spaces if they provide protection from heat and cold around the edges. Stop molding, made from PVC plastic, is a great way to keep the unwelcome temperatures outside. It is simple to install for the do-it-yourself homeowner, and it requires a minimal amount of tools. Below is how you can install stop molding around the exterior of your garage door in just one afternoon:

Tools and materials you will need

• PVC stop molding – stop molding comes in 2-inch widths, and it is usually sold in a variety of colors common to garage doors such as white, brown, tan and green.

• Hacksaw – if you don't have a hacksaw, you can use a crosscut saw or power saw.

• Nine-gauge, 3-inch hot-dipped galvanized nails – if you wish, you may also use stainless steel nails. Just be sure not to use unprotected steel nails, or they may rust due to exposure to moisture.

• Claw hammer

• Utility knife

• Tape measure

• Pencil

• Carpenter's square

How to install the molding

1. Determine how much molding you will need – Measure the horizontal distance across the top of your garage door opening from side-to-side. Then, measure the distance from the bottom of the door opening to the top; multiply this number times two. Next, add this calculated number to the horizontal distance you measured earlier, and this will give you the total length of stop molding needed.

For example, the distance across a single car garage opening is about 9 feet. The bottom-to-top distance of the opening is 7 feet high; multiply 7 times 2, which is 14. Add 14 to 9, which provides a total length of 23 feet of stop molding needed for both sides and the top of the door.

2. Purchase your molding – Choose a color that will match the garage door and trim, or you can paint the molding at a later date if you wish to have a custom color. Molding is sold in various lengths, but try to purchase it in lengths that do not require splicing ends together.

3. Cut the top piece of molding – Using the first measurement obtained in step 1, mark the stop molding at the appropriate length. Use a square to draw a straight perpendicular line across the molding, and cut along the line using a saw of your choice. If there are rough edges or splintering, a utility knife will readily trim away the imperfections.

4. Prepare the top piece of molding for installation– Drive the 3-inch nails into the center of the top piece of molding on its widest side, but stop hammering when the tips of the nails barely penetrate the opposite side. Drive nails approximately every 6 inches along the length of the molding.

5. Position the molding and attach it temporarily – Once you have driven the nails to their initial points, position the molding to the underside of the opening's top trim. Line the molding up so the flap is facing inward toward the garage, and the back edge of the molding is aligned with the trim. Hammer every other nail you drove earlier through the backside of the molding and about an inch deep into the trim; this will permit the molding to be more easily adjusted if you need to make small corrections.

6. Lower the garage door and adjust the molding – Lower the garage door and inspect the fit of the molding flap against the door's face. If it pushes against it and deflects at a 45 degree angle, the seal is sufficient; if not, remove the nails and adjust the molding either backwards or forward so the seal is correct. Hammer the nails back into the trim once you have aligned it properly. Be sure to raise the garage door again after completing this step.

7. Cut the side pieces of molding – Following the same pattern as seen beginning in step 3, measure the lengths of each piece of side molding using a tape measure. Mark perpendicular lines using a square, and cut the molding pieces to the appropriate size. Again, use the utility knife to remove rough burs and edges.

8. Install the side pieces of molding – Drive nails into the centers of the side pieces of molding about every 6 inches, and test fit the molding. Once the molding pieces are cut to the right length, hammer them to the sides of the door trim with the flap facing inward; line up the edges of the molding with the inside edges of the side trim pieces. As before, hammer only every other nail into the trim boards but leave about one inch of the nails protruding.

9. Lower the garage door and adjust the side molding – Removing nails when necessary, adjust the molding so the pieces fit appropriately. The flaps also need to face inward at 45 degrees when the door is lowered; hammer the nails back into the trim once the pieces are aligned. 

If you find that this task is beyond your skill or you are intimidated, contact a garage door repair company.