Local chimney chase cover replacement for Baldwin homes

A quarter inch per foot away from the pipe

One fireplace maker's manual gives the minimum fall for a chase top: at least 1/4 inch per foot, sloping down away from the pipe opening. That may look slight, but it is enough to keep water moving on sheet metal as long as the sheet is stiff enough to hold its shape. A slope that reverses anywhere, even over a few inches, creates a low spot where water sits and the metal stays wet. A level goes on the finished top in several directions, and on a larger chase the sheet gauge is chosen so the slope holds across the span between the supports.

Air openings the termination needs

Some factory-built chimneys are cooled by air moving between their pipe walls, and their terminations have openings for that air. The installation steps for several models carry the same note on their drawings: do not seal ventilation openings. Some chase-style terminations also call for small noncombustible spacers at the corners of the chase, so the chase top sits on them with an air space beneath it.

A new cover has to preserve every one of those openings and spacers exactly as the drawing shows. Sealing them to stop a leak can overheat the chimney, so we trace leaks to their real source and leave the openings alone, as drawn.

Tracing a rust streak to its source

A rust streak on siding points up to its source, but more than one metal part sits at the top of a chase. The cover itself, the storm collar, the termination cap and the fasteners can each rust and streak. The pattern helps: a wide stain starting all along the skirt edge points to the cover, while a narrow streak under one spot may come from a single fastener or from the cap above. We look at each part from the roof and name the source, so a new cover is not sold to fix a rusting cap, and a new cap is not sold to fix a rusting cover.