How to Enclose a Chimney

Measure the roof's pitch. The pitch is the slope, or a measurement of the rise over the run. To measure the pitch with basic tools, use two straight rulers and a level. Set the first ruler horizontally, with one end touching the roof. Use the level to ensure the ruler is completely horizontal and straight. Then set a second ruler directly upright so it touches the free end of the first ruler and the roof, creating a right angle. The second ruler measures the distance between the roof and the free end of the first ruler. That measurement is the rise, or the distance that the roof drops over the length of the first ruler. The run is the length of the first ruler. If, for example, the rise is 5 inches and you use a 12-inch ruler, then the pitch is 5/12.

Set a prefabricated flue wrap or chase cover on its side, and mark the roof's pitch on the wrap or chase. If the pitch is 5/12, then measure 12 inches from the wrap or chase's bottom back corner, and then measure 5 inches up from that point. If the wrap or chase is larger than 12 inches, use a straight edge to continue the line to the end of the wrap or chase. Repeat this step for the item's other side. Draw a straight line along the back to connect the lines.

Cut the roof pitch line you drew by using a circular saw, or whatever cutting tool is required based on the material of the wrap or chase.

Cut a hole in the wrap or chase lid or crown for the penetration of the flue pipe, if necessary, using tin snips.

Install the lid or crown onto the wrap or chase using self-tapping metal screws and a screwdriver, or install whatever fastening mechanism the manufacturer recommends. Install self-tapping screws by setting the screws in place around the edges of the lid or crown and twisting the screwdriver to insert them. Self-tapping screws do not require a pilot hole.

Attach the chimney cover's flange to the cover's base using rivets and a rivet hammer. An option is to use other appropriate fasteners to make the attachment.

Apply silicone sealant around underside of the flange. Secure the chimney wrap or chase to the roof by using galvanized lag screws and a nut driver, or use other fasteners as directed by the product's manufacturer. Apply additional silicone sealant around all bottom edges of the enclosure and to the seam between the chimney pipe and lid or crown.