Chimney Flashing
Chimney Flashing Leak Diagnosis by Rooftop Inspection

Chimney Step Flashing Leaks

Horrible chimney flashing at the roof surface is shown in these photos which are remarkable for the number of errors, the leak history at this home, and the chances of related damage to the surrounding wood structure from insects or rot, or damage to the chimney itself from frost.

The new roof was installed with a bare half-inch of vertical side flashing along the chimney and no counter flashing. The previous roof or chimney flashing was installed with no counter flashing, relying on roofing mastic to seal this juncture. Cracks and openings at chimney flashing admit wind-blown rain into the structure.

An inspector with binocular vision might have found this crazy flashing installation from the ground. Maybe.

[Click to enlarge any image]

Watch out:  older asphalt-based roofing mastics and sealants may contain asbestos.

See MASTIC, CUTBACK ADHESIVE, FLASHING CEMENT ASBESTOS.

The illustrations above & below, courtesy of Carson Dunlop Associates, show chimney flashing details when there is NOT a chimney saddle or cricket as well as where some of the trouble spots occur.

Chimney Saddle or Chimney Cricket Flashing Can Prevent Roof Leaks

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Above: a chimney located in a roof valley obstructs roof drainage, invites roof leaks, and ultimately chimney damage that can make the chimney unsafe, risking a buidling fire or fatal carbon monoxide poisoning.

Where chimneys are broad in width (30 inches or more) or located too close to a valley or other obstruction (photos above), the raised ridged structure shown in Carson Dunlop Associates [at REVIEWERS] sketch (above left), alternately called a chimney cricket or a chimney saddle (illustrated below), can significantly reduce debris collection at the chimney-roof intersection on the up-slope side of the chimney as well as reducing the chances of leaks at this otherwise common roof leak point.

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Our photo and Carson Dunlop's sketch above show a typical chimney saddle or cricket, installed.

Don't walk on this structure. Some chimney saddles or crickets are supported only sufficiently to shed water but not for foot traffic.

When inspecting the chimney for leaks look closely at the chimney cricket or chimney saddle for metal fatigue cracks or other damage.

Additional details about roof flashing inspection, defects, and repair are

at ROOFING INSPECTION & REPAIR

Suggested Details for Roof Saddle / Chimney Cricket Construction

Question: How about some details on roof saddle construction?

[Paraphrasing: On a messy re-roof job that includes a roof section with lots of penetrations, we are cleaning up the roof design to reduce the leak risk by constructing a roof saddle or cricket.]

I see reference to "crickets" all over... your site mentions them on "Flashing & Sealing Specifications for Exposed Fastener Metal Roof Systems" page. But I have been unable to find specific instruction... models, diagrams etc., on how to build these things. What I do see around here is a lot of metal roofs.

The roofs I've checked out with the same issues that I'm asking about (vertical wall on downside slope of a roof) all were done without crickets. And every winter, I see a bucket of Henry's tar up there trying to patch the leaks. So if you have a reference for building crickets or a good book I'd sure appreciate it. -- Jim McKay, November 2010

Reply: Build a Tiny Intersecting Roof Gable, Standard Chimney Step & Counter Flashing, Valley Flashing, careful sealing

We hadn't previously thought about giving specific build instructions for a chimney cricket or roof saddle, perhaps because building a saddle is a duplication of the framing for roof construction of a tiny intersecting gable - standard carpentry.

As you'll see in our photos of chimney saddles above, the cricket or saddle will form an intersecting gable that butts against the up-roof side of the chimney.The devil is once again, in the details of forming and sealing flashing to avoid leaks from water or in some climates melting snow on the up-roof side of the chimney. A chimney saddle also avoids the accumulation of debris, leaves, etc. that shorten roof life in that area.

The length of the ridge of your cricket (or saddle) will determine the height of the cricket at the chimney and the point at which that ridge contacts the main roof slope. We make sure that the cricket ridge is long enough that the height above the roof at the chimney is high enough that we have a decent slope, 6 in 12 or more, to assure good drainage around the chimney.

Of course the total length of the saddle ridge is limited if you don't have a lot of roof distance up-slope from the chimney itself. In that case the ridge of the cricket will come to the ridge of the main roof. And of course your cricket (saddle) ridge is framed level.

If the total cricket size is small, just a few feet or less, it's probably easiest to simply construct the entire supporting structure for the cricket out of 1x lumber.

Larger crickets would be framed using 2x lumber and roof sheathing. Remember that maybe not you, but someone is likely to step on the cricket sooner or later, perhaps while repairing or cleaning the chimney. So flimsy saddles and crickets are a bad idea.

Once the chimney saddle has been built and nailed into place on the main roof slope, you can proceed to cover it with metal flashing, ice and water shield etc. and then a metal cover or roof shingles or another covering that matches what's on the main slope. Some roofers cover large crickets with shingles or roll roofing, but we prefer solid metal or a membrane such as modified bitumen.

If you are using shingles on the cricket surface, flashing at the abutment of the cricket to the up-roof chimney side will be formed using step flashing (one per shingle) and typically a single piece of counter flashing for each side of the cricket.

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Your flashing will need to extend no less than 4" up the chimney face, and be covered by counterflashing cut into (a "reglet) the chimney face and sealed.

When you are flashing the valleys formed by the cricket sides, follow normal valley flashing design details, being sure that the flashing is both built with a hooked edge, cleated 12" on center, and sealed to the shingles on the main roof so that water doesn't run down the cricket and under the roof shingles.

If you're covering the whole cricket with shingles, then the cricket ridge is shingled like a roof ridge, with the last ridge cap shingle where the cricket ridge meets the main roof slope done the same way as a lower roof ridge would meet a main upper slope - the last shingle has to be split, and sealed, before the shingle on the main roof slope course covers it up.

Make your flashing the feature that keeps water out of the roof. Don't rely on caulks and sealants.

Cracked Brick Masonry Chimney Sides

Thin Cracks in Brick or Masonry Block Chimneys

Cracked chimney masonry such as shown in this photo of cracks in a brick chimney exterior, may a safety concern if the flue liner or chimney are not intact and fire/gas safe.

Cracks in a brick masonry chimney such as shown in these photographs may be caused by improper original chimney construction. This damage also appears on concrete block constructed chimneys.

See CHIMNEY CRACK DETECTION & DIAGNOSIS for details about inspecting and diagnosing types of chimney cracks and movement.

WARNING: Cracks in a chimney can be very significant and dangerous, risking fire or chimney collapse. Be sure to review the articles

at BRICK CHIMNEY CRACKS & COLLAPSE.

Question: What should I do about ongoing flashing leaks at my stone chimney?

This topic has moved to STONE CHIMNEYS, FLASHING, LEAK REPAIR

Metal Flashing & Storm Collar for Round Metal Chimneys & Flues

Moved to METAL CHIMNEY FLASHING & STORM COLLARS