A proper chimney cap is one that shelters and protects the entire masonry crown footprint and all terminations, with a screen to keep our pests and debris. A masonry chimney is a clay porous structure that absorbs water and becomes saturated in the PNW climate. In this saturated state, masonry decay is accelerated. It is regular exterior building maintenance to apply a water sealant to any masonry structure every 10 years.