- 1). Measure the opening for the new doors before you purchase them. If your existing exterior door opening is six feet wide by seven feet tall, which is average, you'll want to purchase new doors that are close to this size to avoid excessive demolition and patching of your walls.
- 2). Buy the door. Most French door units are sold as pre-hung units, which means that the door and the frame are packaged together and easy to install. The variety of French doors available for purchase is limitless. These doors are available in every color, finish, wood veneer and glass panel combination you could desire. You can purchase these units at your local home improvement store or from a door distributor such as Trustile or Masonite.
- 3). Frame out the rough opening for your new door. Remove the existing door, if applicable, and place it aside for disposal. Use the instructions that came with your new French doors to determine the required rough opening size. You'll want the rough opening to be one-half inch larger in height and width than your new door unit. This may require adding or removing the 2 by 4-inch boards or existing structural framing components.
- 4). Slide the pre-hung unit in the opening, bottom first, making sure it is centered within the opening. Use three nails on each jamb to temporarily hold the unit in place, but do not hammer these nails all the way in yet.
- 5). Make sure the door is level. Check to see if the spacing along the jambs is even from top to bottom, and along the head of the door frame. If it isn't even, use wooden shims to create equal spacing. Then use the level to check the plumbness of the jambs and head again. Use more shims if the unit is not level.
- 6). Finish nailing the unit in place. Once you are confident the doors are level, use nails along both jambs to nail the unit in place. Countersink the temporary nails you used earlier as well, and use nails to secure all shims.
- 7). Weatherproof the opening. Place insulation in the gap between the door jambs and the wall framing, then install the wood casing or trim for the door. Finish the installation with a caulk joint on both the interior and exterior of the opening where the door frame meets the wall.
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