How to Construct a Fireproof Safe

Assemble a plywood box using 1-inch thick plywood cut to your needed size. Make sure when cutting panels for the box you're accounting for the thickness of the plywood. For example, if the sides are 10 inches by 10 inches, then the bottom and top need to be 8 inches by 10 inches, and the back wall and door will need to be 8 inches by 8 inches. Using fire-resistant nails, attach all but the door together so you will end up with a 10-inch by 10-inch box.

Sand the inside edges of the door piece to about a 45-degree slope. This will help prevent the edges from catching when opening and closing the door. Attach the two fire-resistant hinges along one edge of the same side of the door that you just sanded. Secure in place with fire-resistant nuts and bolts, keeping the nut on the side you're placing the hinges. Attach the door by the hinges to the plywood box. You may have to shave the edges to ensure a perfect fit.

Cut sheets of fire-resistant type X gypsum board to fit on the inside and outside of the plywood box. This will be fairly easy for all but the door. Take time and care to ensure you're accounting for the hinges and clearance needed for the door to open and close.

Drill through all the layers of gypsum board and plywood on one side of the door and the touching side of the safe wall to attach a fire-resistant lock bar. Secure in place with nuts and bolts. Be sure that all the nuts are found on the inside of the safe to ensure safety. Lock the lock bar with a fire-resistant combination lock.