Power Washing Shingles?

Posted by in Apparent Mold/Biological Growth, Buying/Maintaining a Home, Roof, Shingles | June 07, 2014

Looking to high pressure wash (power wash) all that dirt, discoloration, mold growth, lichens, etc. off your shingles?  Have you seen advertisements in various local papers regarding high pressure washing shingles?  Here are a few observations.

We have the experience of examining many asphalt shingle roofs.  On occasion we have come across an asphalt shingle roof that has been power washed.

Some power washes have been done well, cleaning the surface without causing any apparent visible damage.  We have seen other roofs where the power washing did not result in the expected appearance after the washing or were even damaged by the power wash.

High pressure washing not only removes dirt, discoloration, mold growth, lichens, etc., but can also remove granules, reducing the service life and/or altering the appearance of the shingles.  We have observed this especially where the power wash was used to remove mature biological growth, such as, lichens.


Granules, some previously loosened by lichens, washed off shingle surface.


It is very difficult to control the application of the spray for a uniform cleaning and to achieve a clean surface without causing damage.  We have seen roofs with paths or patches of cleaned surfaces.  And when used to clean lichens we have seen where there are still remnants of the lichens, waiting for the right conditions to sprout.  Leaving portions of the biological growth behind is like pulling off the top of a weed and leaving the root behind: the biological growth will re-emerge.


Streaks & spots from incomplete power washing.


Lichens still present on shingles surface.


The damage producing power washes that we have observed were generally done by the home owner himself or other inexperienced friend of the home owner.  So, if you are interested in power washing your asphalt shingles, be aware of these possible issues and it may be best to leave it to an experienced professional.