Abstract: A unitary impervious boot member which includes a lip portion at the bottom thereof, which is fitted in substantial close tolerance around a chimney's flu tile. The lip portion of the member is sealed to the base of the upwardly extending flu tile by elastical pressure and optionally with adhesive such as silicone. The tightly fitted unitary impervious boot member is received and counterflashed by horizontal impervious member which substantially covers the entire horizontal surface of the sloped inner chimney structure before the cap is installed; and is sealed thereto by the gravitational pressure of the subsequently installed chimney cap and optionally with an adhesive such as silicone. Breathable weep lines are placed on top of the counterflashed horizontal impervious member to provide an exit for any trace moisture that may have penetrated the chimney cap.