Brick and mortar chimneys are a common site on rooftops of a certain age in Washington State. A common point of deferred maintenance and long term damage is at the chimney cap. This is the mortar cap at the top of the chimney that protects the top of the chimney and bricks below.
Water tends to pool and collect on the top of the chimney cap. This can lead to moss growth and erosion of the mortar which over the long term leads to cracks and cap failure. Eventually the cap will split and be in danger of falling off the chimney on to the roof or to the ground below.
If a chimney cap is at the point of damage like in these pictures, it needs to be repaired or replaced. Preventative maintenance is the regular cleaning of moss and the installation of a rain cap over the flue that extends over the edges of the chimney.
Brian Jovag, owner of Jovag Home Inspection.