Step 1
Measure the amount of chimney that is exposed above the roof line. Cut two pieces of reinforcing bar twice the size of the exposed chimney, using the hacksaw. Cut two pieces of reinforcing bar to the size of the exposed chimney.
Step 2
Insert the two longer bars through the roof and along the chimney on the two sides that are surrounded by vertical studs. Check inside the house if necessary, to determine the correct sides.
Step 3
Place the shorter bars on the other two sides of the chimney. Connect all four bars together with metal cables.
Step 4
Screw a metal strap to the chimney inside the house, where the chimney exits the house to the roof. Run the strap around the chimney and screw it in place onto a roof joist.
Step 5
Rebuild the chimney if it is has a crack deep enough to penetrate all the chimney's layers. Remove the chimney completely. Retrofit a steel liner from the throat of the firebox to the roof and rebuild around the liner. Use horizontal reinforcing metal ties and vertical reinforcing bars as you get toward the top. For each foot that the chimney extends from the roof, you must reinforce inside the house a corresponding amount. For example, if your chimney extends 3 feet above the roof, the total amount of chimney requiring reinforcing is 6 feet. Place vertical reinforcing bar at each corner, and fill in the channels with nonshrinking grout.