Unless the chimney is installed directly on the ridge (peak) of the roof, every chimney should have a cricket. The reason for installing a cricket is it will divert rain water directly away from the back of the chimney. It relieves the job of the chimney flashing somewhat by not having to come in direct contact with rain water, running down the roof.
A chimney cricket is metal or wooden built, triangular or diamond-shaped structure designed to divert or direct away from the base or back side of a chimney. A wooden constructed cricket consists of several pieces of 2″x4″ lumber cut to the size of chimney and plywood. Since the plywood sides only have to re-direct water, the plywood can be as thin as 3/8″ thick. The plywood is fastened to the 2″x4″ frame forming a diamond or triangle shape depending on the size of the chimney.
Upon completion of the structure, “ice and water shield” underlayment is placed approximately 6″ up on the wall of the chimney and folded on the newly installed plywood cricket and then onto the original roof deck. The back of the “ice and water shield” is sticky so it can be easily self-adhered to the plywood. New metal step and counter flashing is installed directly to the chimney. The counter flashing is caulked on the top edges to prevent water from infiltrating from the chimney walls. The job is finished with shingles matching the original roof, including a shingle cap for the top of the cricket.
If installed correctly, the new chimney cricket will deliver water-tight, worry-free service for years to come.
Does your chimney have a cricket? If you discover you do not have a cricket behind your chimney, contact a roofing professional for a free evaluation and estimate.