How to Install a Lintel for a Window

A lintel is the horizontal framing board on the top of the window frame. In post-and-beam construction, the lintel is the load-bearing portion of the window opening and rests on top of the side posts of the window frame. The lintel is often a decorative feature on this type of window. It is installed before you install the window and locks over the posts with mortise and tenon joinery. The lintel has a mortise or slot at each end. The side posts have a tenon or peg that slides into the mortises in the lintel.

Things You'll Need

  • Mortise Machine
  • Fine-Grit Sanding Pad
  • Lintel Board
  • Pencil

Center the lintel board over the top ends of the side window posts. The lintel must be aligned the way you want it to appear once installed.

Mark the location of the tenons on the top ends of the side window posts onto the bottom side of the lintel board with a pencil.

Place the lintel board on the table of a mortise machine with the bottom side up so that you can see the pencil marks. The marks indicate where the mortises need to be cut in the lintel board. A mortise is a slot cut through a piece of wood.

Line up the mortise chisel with the pencil marks and pull down on the handle to cut through the wood. Make as many passes with the mortise machine as needed to complete the mortise on each end of the lintel.

Sand the lintel on all sides with a fine-grit sanding pad. Align the mortises in the lintel over the tenons on the ends of the side posts and slide the lintel over the side posts.


  • Select a quality hardwood beam with a decorative appearance such as reclaimed woods that have a lot of character from age.


  • Wear eye and ear protection when operating a mortise machine.