How Chimney Flashing Protects Your Home

The flashing that wraps the base of your chimney is probably one of the most inconspicuous components of your chimney system. Yet when flashing is damaged or missing altogether, it can quickly become a very visible and critical issue.

Roofs and chimneys are separate structures with a gap between them. While this gap usually isn’t wide, it’s more than sufficient to allow water to run down through it. Preventing this intrusion is the job of chimney flashing.

Chimney Flashing Repair In Milford, NHWhat is chimney flashing?

Flashing is usually custom-made from sheet metal to properly fit around the base of your chimney. There are two layers: step flashing and counterflashing. Step flashing is L-shaped and installed to seal the roof/chimney gap by weaving it into the shingle courses. Counterflashing is then installed by embedding it into the chimney mortar joints and pulling it down to cover the top gap of the step flashing.

When installed correctly by an experienced chimney technician, flashing will effectively keep water from rain and melting snow out of your home.

Water damage from missing or defective flashing

Although you can’t see what’s below the roof/chimney gap, you can imagine what water will contact when it spills through. Intruding water can affect the roof, ceiling, wallboards, insulation, and the exterior of the chimney down inside the home.

Standing water against these materials will cause decomposition. Wood can start to rot and harbor mold growth; metal can rust and decompose; chimney bricks can begin decaying and lead to a dangerous structural compromise that could collapse the chimney or pave the way for a chimney fire.

Chimney flashing quickly becomes a critical component of your chimney system when you consider that early damage caused by a flashing problem is damage you can’t see – because it’s all happening within “invisible” areas of the home. By the time the problem becomes obvious, you can be looking at huge repair, restoration, and mold remediation bills.

Chimney damaged in Nashua, NHSolving the flashing issue

Fortunately, while flashing is a critical component, it’s also one of the easiest parts of a chimney system to fix and install. As a homeowner, you can perform annual or semiannual visual inspections of your chimney flashing, checking that it’s secure against the chimney and the roof and watching for signs of rusting and warping. Professional chimney inspectors also will take a close look at flashing each time they do an inspection.

(Flashing and all other chimney components including the masonry should be inspected by a CSIA-certified technician once a year). At one point, you’ll probably need to have your chimney flashing resealed or replaced. This is a fairly quick and inexpensive job that will be over before you know it and will possibly save you thousands on repair costs because of water damage. If your chimney flashing is in need of repair or you need new flashing, the experts at Black Moose Chimney & Stove of Antrim, NH, are ready to help.


We provide chimney repairs, component replacement, brickwork, chimney inspections, and chimney sweep services. Contact Southern New Hampshire’s chimney leaders at (603) 525-7905.