The ashing is a movable joint that makes a weather-tight seal between the roof and the chimney. There are several types of ashing construction. The most common type is referred to as step ashing. Step ashing can be made from a variety of metals, including stainless steel, aluminum, galvanized metal, and copper. Step ashing is a two-part system. The rst part is usually a square piece of metal folded at a 90-degree angle. One side of the piece of metal is installed under the ashing attached to the roof and is covered by the roong material. The bend is placed against the chimney. This forms 1/2 of the ashing. The other is a piece of metal that is attached to the chimney and covers the ange of the rst piece that is attached to the roof and is up against the chimney. This is called counter ashing. These are usually installed in a series that gives the appearance of steps. That is why it is referred to as step ashing. The best practice is to install the counter ashing into a mortar joint with a fold in the metal and part of the metal being inserted into the bed joint of the mortar. This is usually sealed with mortar or a exible sealant.

Your chimney moves with changes in temperatures and weather conditions. Your roof also moves with changes in humidity and weather conditions. The roof and the chimney do not move at the same rate. This difference in the rate of movement is why the ashing needs to be a movable or exible joint. There are other types of ashing materials that are usually exible elastomeric sealants. There are several brands on the market with varying qualities and application methods. It is important to remember that the ashing compound must be non-combustible.

A cricket sometimes referred to as a bib or saddle is a small roof that is constructed like a dormer up against the back side of the chimney. The purpose of this dormer-style roof is to divert water and snow around the chimney.

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