Building Mantels for a Three-sided Fireplace

A fireplace.
  • 3-4 hours
  • Intermediate
  • 100-150
What You'll Need
Tape measure
Utility knife
Carpenters glue
Caulking gun
Small nails

A three-sided fireplace can either be gas, wood burning, or electric. Since the flame can be viewed from three different angles, a three-sided fireplace is often used as a design element in a home. A three-sided fireplace is also known as a peninsula fireplace as they are often square with the fourth side attached to a wall. This is where the gas or vent is attached. Building a mantel for a three-sided fireplace is a unique endeavor. Standard mantels surround the entire fireplace while mantels for a three-sided fireplace typically cap the fireplace.

Step 1 - Take Measurements

Due to the shape of the three-sided fireplace, measurements become very important. You can build a mantle for just the fireplace but you may also build it to expand over the section attached to the wall. The decision is up to you due to the design differences found in these types of fireplaces. Measure the length and width of the top of the three-sided fireplace. Include the return of the fireplace if you intend to include a mantle for it.

Step 2 - Cut the Wood

You will be using plywood for the base of the mantle. Use the measurements you took down in Step 1 and transfer them to the plywood. Cut the plywood and then place it on top of the three-sided fireplace. Make sure it fits perfectly on top of the fireplace. Choose a decorative wood like cedar or mahogany for the rest of the mantle.

Cut a piece out to the exact same size as the piece of plywood. This will be the top of the mantle. Determine how high you want the mantle to be and cut out pieces of wood for each of the sides. Add an additional ¼-inch to the height as the mantle will be more like a cap. Use the router to carve out any designs you may wish to have in the mantle.

Step 3 - Assemble the Mantle

Place one of the sides on a work surface and measure ¼-inch from the bottom up and then draw a line. Place a line of carpenter’s glue along it and then place the plywood in place. Repeat with the other sides. Nail them together for added support. Glue the top on and then nail it in place. This is a very basic mantle for a three-sided fireplace. You can use many different kinds of wood as well as other materials like stone. You can also carve any design you like.

Step 4 - Install the Mantle

Lift the mantle and set it on top of the three-sided fireplace. It will rest on the mantle and the small lip will secure it in place. Apply a bead of heat-resistant silicone caulk to the underside of the mantle where the wood meets the fireplace.