Yes, algae can form on fiberglass shingles. In fact, all shingles can be prone to this given the right circumstances.

Traditionally, fiberglass shingles resist algae better than organic asphalt shingles. Moreover, in recent years, manufacturers of fiberglass shingles have started adding copper granules into their shingles to better fight algae.

I would recommend contacting the manufacturer (local rep) and asking about the procedure they recommend.

If the problem is not too severe, you could try a pressure washer with a mild detergent. Make sure you spray down the roof from the top – not from the bottom up. Cleaning from the bottom up means you will drive water under the shingles and cause leaks or damage. Also, take care to use moderate pressure to ensure you don’t blow off the ceramic granule coating.

Installing a zinc or copper strip along the peak and hips, under the capping can bleed oxide onto the roof which may help resist formation.

If the problem is too extensive, replacement may be your only option, particularly if the appearance of the roof is important to you.

Can algae be removed from asphalt shingles? – Glenn, Richmond Hill

Craig’s response – “No, cleaning algae from asphalt shingles is not recommended”

I am not aware of any product on the market today that would effectively remove existing algae from asphalt shingles.

Pressure washing (as is sometimes done on cedar shingles) may work, but there is a big risk that the cleaning would damage or remove the ceramic granules which coat the surface of the shingle. In addition, if the shingles are brittle, you run the risk of blasting them right off the roof!

Our production manager suggests that lime dust mixed with water may be effective, but once again, there is a risk that the cleaning mixture may discolour the shingle. You also need to know that lime dust is not readily available in Canada, but is easier to find in the U.S.

Another suggestion is to contact Spar Marathon Roofing Supplies (Milt @ 905-391-5891). He may be able to suggest a product. Commercial products such as CLR may work but under no circumstances use any product that is solvent based. The shingle manufacturer may have some suggestions on this.

The better solution in the long run is to switch to algae-resistant fiberglass shingles, which are available from our shingle supplier, Certainteed. These shingles contain copper granules which bleed oxide onto the shingles, which helps prevent the formation of algae. Also, using copper or zinc flashing details at the top of your mansard can bleed oxide onto the shingles.