The reciprocating saw (sawzall) is an excellent tool for chimney construction. In these Chimney Flashing Details, we will cover many details on how to safely and properly install flashing. Where a chimney passes through a roof, make a 2-inch clearance between the wood framing and the chimney for fire protection. This will also leave room for expansion due to temperature changes, settlement and slight movements during heavy winds. When installing flashing think of it as though you were installing shingles. Water is going to flow down this, how can I make it so it will not get down between the chimney and the framing. Flash and counter flash to make the junction with the roof watertight.
In these Flashing Details, you will begin with the base flashing at the downslope side of the chimney. Make the flashing 12 inches longer than the width of the chimney and at least 24 inches wide. Cut and install the base flashing with a pair of tin snips. Next cut pieces of step flashing 10 inches square. Bend them more than 90 degrees so they will press against the chimney. Cut and fold the first piece of flashing so it wraps 1 to 2 inches around the front of the chimney. Work up the chimney, lapping each piece of flashing at least 2 inches over the one below. Fasten the flashing with 1-1/2 inch nails or screws.