Local chimney chase cover replacement for Brentwood 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.

Folded, welded and sealed seams

One-piece chase tops have seams only at their corners, where the skirt folds down. A very large chase, or one with an unusual shape, may need two sheets joined across the top.

Every seam is a possible leak, and fireplace manuals call for caulking all seams on the chase top. Corner seams are folded so water runs over them rather than into them. Joints across the top are folded and locked or welded, then sealed, and placed where water runs across them rather than along them. Fewer seams in the flat means fewer places to fail, which is why we cut one sheet where the chase size allows.

Testing the new top with water

A new chase top is shaped to drain, and water is the simplest proof. Where the roof gives safe footing, a garden hose is run over the finished top, first at the collar and then outward toward each edge, while we watch where the water goes. It should leave from every side and drop off the drips without standing anywhere.

If an attic hatch or access panel gives a view into the chase, someone watches inside for drips at the same time. Any top that holds water is reshaped on the spot, and the test result goes on the paperwork we leave with you.