written by: Mike Gosser

Today I will go over part one of, “EXTERIOR DOORS.” I want to make sure I give the necessary time to best explain both. Part one will explain  about door slabs and how to install them properly and part two will thoroughly explain prehung door units.


EXTERIOR DOOR SLAB:  First lets talk about the doors themselves. Door slabs are usually 1 3/4″ in thickness. They can be ordered  thicker from the mill or made thicker on the job site by applying boards to the face of the door. The exterior jambs will need to be deeper to accommodate the thicker doors and will need larger hinges  (possibly more of them).  These doors can be ordered in a variety of styles and wood species.  The exterior doors can be made of pine, fir, oak, metal and fiberglass.  Fiberglass is a good choice because it is resistant to rotting, but is very limited in style choices and the type of wood that you may desire. When choosing the style and wood type, I say, “Shoot for the moon, then work your way back.” When checking the price, always compare pricing from a few different suppliers.  You may be surprised how the pricing may end up. FYI – I prefer fir because of its coloring, grain and stability. I sometimes make a slurry with instant coffee and wipe the door down to create a patina before finishing the door. Of course this is subjective.

INSTALLATION GUIDELINES:  Note – The term frame and jamb can be interchangeable. If you are only replacing the door slab and not the exterior frame, you will need to measure your door opening or the existing door. I like to measure the jamb opening. It’s the routed part of the frame that has the weatherstrip nailed to it and where the door actually sits when closed. First lets measure the width part of the jamb. It’s the measurement between the hinge part of the jamb to the striker plate part of the jamb. The height is measured from the metal threshold to the top part of the jamb. A front door measurement usually is 36″ wide x  80″ high or could be 84″ high x 1 3/4″ thick. Retailers like to use door measurements in feet and inches. For example, the previous measurement would be a 3′ 0″ x 6′ 8″. Your salesman should understand what size you need if you specify the measurements in inches. Rear doors are usually 32″ wide. If you need to know which way the the hinge swing swings, put your back against the inside of the door and swing your arm/hand that the hinge is on. For example,  if the hinge is on your right side , put your back against the door, swing your right arm/hand the way the door swings. That’s a right hand swing. If you are using your left arm/hand its a left hand swing. Before you start machining your door, I recommend removing the old threshold. Doing this will help make the fitting part of the installation much easier.

Important to remember, the lock-set edge and the top edge of the door edges must be cut at  a 3 degree angle if you have a traditional metal weatherstrip attached to the jamb. The longer side of this angle cut starts at the exterior edge of the door.

Before you cut the hinge pockets, mortising the hinge, or drilling the lock-set holes, you need to fit the door into the existing opening. Never plane the hinge side. Using a rafter square, hold the body (the longer side of the square) against the hinge side of the jamb to check the top of the door jamb to see if it is square. Always mark the hinge side of the door and the inside of the door for reference. Now lay the body of the rafter square on the hinge edge of the door and mark the same angle on the face of the door that shown when you check the top of the jamb with the square. Now cut, if necessary, the top of the door at the same angle as the top of the jamb.  Make the width of the door 1/8″ smaller than the jamb opening width. If your lucky, you will not need to do this step. This measurement is from the hinge part of the jamb to the striker plate side of the jamb. I suggest purchasing a new aluminum exterior threshold and follow the manufactures instructions to fit the bottom of the door. Before you make the threshold cut, put the door into the opening and mark with a sharp pencil the hinge locations. Mark the hinge outline with a butt marker. Mortise the wood inside the outline marks to the depth of the hinge thickness. This is usually about 1/8″ deep. Now you should be able to install your door and check for fit. Next mark the center line from striker plate onto door. This is the center line of your lock-set. The bore offset is usually 1 3/4″ from the edge of door, and the size of the bore is usually 2 1/8″. Not all lock-sets are the same and these measurements need to be verified from the old door. If you purchase a new lock-set, follow the manufacture’s instructions. After installing the lock-set, remove the door and proceed to install the threshold and cut the door according to the instructions that come with the threshold.

Note – If you want to supply the door but want a contractor to install it, a reputable contractor will verify all dimensions and specifications before you place your order.

SAFETY FIRST!  DONT FORGET!  Always read and follow the safety instructions that come with your tools, equipment and supplies.

Leave any comments and or questions in our form on the right. Next week I will discuss prehung exterior doors.