Roof stains are not only unappealing to look at, they also compromise the waterproofing ability of your shingles. Algae, tree sap and leaves, moss, and many other materials get dropped or blown onto your roof. These substances can infiltrate the limestone mixture that attaches the shingle to the roof, and end up harming its ability to repel water. A clean roof is not only more attractive, but safer.
Step 1 - Cover Foliage
Since you’ll be working with a bleach mixture, make sure that any greenery in the vicinity is covered up to avoid possible harm.
Step 2 - Take Safety Precautions
The most important part of cleaning your roof is making sure you’re safe. Fungi and other stains on the roof become slick when wet, so you’ll need to wear a harness or safety rope, hard hat, and have a sturdy ladder nearby.
Step 3 - Mix Cleaning Solution
There are a few ways you can mix bleach, but the most common is to take one part chlorine bleach, three parts water, and a sprinkle of liquid laundry detergent or TSP. Mix these ingredients well in a large bucket so the solution can be applied evenly.
Step 4 - Apply Solution
After mixing, spread the solution on the shingles with a spray pump or soft scrub brush. You may apply gentle pressure to the stained areas, but do not scrub quickly or with any force. If you do, granules will come off the shingle and affect your roof’s waterproofing.
Step 5 - Let Solution Soak In
When you’re confident the roof is completely covered with the cleaning solution, you can come down and relax for the next 10 to 15 minutes. Now is a good time to make sure your greenery is still protected.
Step 6 - Wash Roof
Unless you are on scaffolding or a walkway near the roof, you should wash the solution off from the ground. Only use a garden hose with normal pressure, as using a high-pressure washer will strip granules.
Step 7 - Let Dry
Allow your roof ample time to dry off, and then check on it. If there are no more stains on the roof, you’re done. In the case of residual stains, you can apply more of the solution and let it soak longer before rinsing off.
Step 8 - Future Prevention
Cleaning your roof is definitely effective and will prevent you from having to replace it sooner than usual, but the fact remains that it will become stained again. There are many ways to keep certain algae or fungi from making their home on your roof.
Copper strips are one way. They work by spreading trace amounts of copper during a rainstorm—the strips are positioned at the topmost part of the roof so that when it rains, the copper rolls down and kills budding fungi. Check your local hardware store to see what products are available for the types of stains you have.