I have a house with an existing open wood fireplace. It was a double (back to back separated by a wall)fireplace but it has been turned into one only (lounge room). The chimney is brick and travels up between the wall and stops just underneath the roofline. I believe it is a standard chimney size. A 4 inch fule has been put on it to extend it past the roofline and past the peak of the roof. Since it is on an angle water gets in when it rains and at times birds as well. The fireplace operates properly when I have a roaring fire, but as it dies down smoke comes inside. I am thinking of extending the brick chimney myself. Is this a good idea? I believe that I need a cap or damper or cowl. Which should I use?