Residential Roofing Tips

Why is My Asphalt Shingle Roof Stained?

Ever wondered where that black staining on your asphalt shingle roof comes from? And even more importantly, how to fix it? If you answered yes to either of these questions, then this post is for you. If you are a new homeowner or new to asphalt shingles, you may not be familiar with how to handle the stains that can build over time. Let’s break down how the staining gets on your roof, where it comes from, and how to resolve it.

Roofing materials all have their pros and cons and almost all roof types are susceptible to discoloration. Something to keep in mind if you have an asphalt shingle roof, or plan to have one installed soon, is that staining will occur. The black staining is unavoidable and is something you’ll need to maintain over the years.

What are Those Stains?

The black stains on your asphalt shingles are actually caused by blue-green algae. It feeds on the limestone found in the shingle granules. The good news is, it’s only a cosmetic issue. It might be unsightly, but it shouldn’t ever affect the performance or longevity of your roof.

An additional issue that we often see is moss growth. The blue-green algae give the moss a foundation to grab onto, and this can be a growing issue (pun intended!) if you don’t address it in a timely manner. Remember that any surface that is damp and warm without direct sunlight can support algae growth.

How to Treat Algae Growth on Your Roof

There are several options for avoiding and treating algae growth on asphalt shingles. Most asphalt shingles on the market today are made with algae-resistant compounds. The granules in these shingles are coated with zinc or copper oxide which kills algae and prevents staining and moss growth. For homeowners considering this option, it’s important to note that the algae resistance on these shingles will only last about 10 years.

If you already see algae staining on your roof, you can opt to clean it. One option is to clean using a DIY solution made from bleach, water, and trisodium phosphate. The ingredients may vary between shingle manufacturers and solutions range from one-gallon bleach, five gallons of water, and a dash of TSP to 2.5 gallons bleach and water and 1 cup TSP. Spray the solution on the roof, let it sit for 10-20 minutes, and rinse off with a garden hose. NEVER POWERWASH your asphalt shingle roof. Keep in mind that cleaning the shingles isn’t a permanent solution and you’ll need to repeat the process every 3-5 years.

Cleaning a roof can be a difficult and dangerous job and we recommend hiring a professional to tackle it for you. There are numerous roof cleaning services out there and we’re glad to provide recommendations. Contact the Bond Roofing team if you’d like to speak to a team member about your roofing needs.