How to Clean Algae from Roof


My 18 year old wood roof shingles have algae here in Northern NJ. I got several quotes and they were all very costly (about $5,000) to clean the roof using diluted bleach.  Should I wait until need a new roof and replace with long life shingles?
dsaks 12-9-07 8:31pm

Algae and fungus on your roof is unsightly and in the case of wood roofs, will impede draining keeping the roof shingles saturated and shortening their life.  That being said, roof cleaning, done improperly, can destroy a roof, or the landscaping around it.  First, you need to be careful not to “scrub” wood shingles, either by hand or with a pressure washer.  As I’m sure you know, wood shingles are softer than asphalt and you could very easily scrub away enough of the wood fibers to shorten the life even more.  Plus, bleach based roof cleaners have to be used very cautiously as the bleach can kill the landscaping right under the roof’s edge.

A better solution might be to use Roof Reviver, a product you can order online and apply it yourself with a garden hose.  Roof Reviver specifies a process they call “gradual removal” which with one or more applications with a garden hose stop moss growth in its tracks.

Spending $5,000 on an 18 year old roof would be a total waste of money.  Given an average roof life, you’ll be replacing it sooner rather than later and the 5 grand won’t buy you enough additional years to make it worth your while.  When it does come time to replace the roof, be sure to choose asphalt shingles that contain an algaecide which will slow the future growth.  Also, trimming back tree that overhang and shadow the roof can also help as the ultraviolet rays of the sun are the best algaecide nature has to offer!

Reaching Tom:  If you have a home improvement question or comment on this topic, please post it below.  For answers to other home improvement questions, please email Tom at so your question can beused in future blog entries, or search Tom’s home improvement articles at

Leave a Reply