3 Nature-Related Causes for Roof Stains

When your roofing material has dark spots or moldy-looking areas, your whole house looks dingy. A variety of natural issues can cause stains on rooftops. Here are three common causes of roof stains courtesy of the natural world.

Tree Sap Stains

Tree branches that grow over roofs drop plant material throughout the year. All trees dribble a bit of sap, but some trees drip larger amounts of sap onto cars, yards, and rooftops.

Sap is a sticky syrup-like substance that attracts debris, so drops of sap soon collect small branches, leaf matter, and other dirt on the surfaces of the dribbles. The sap spots on your roof may start growing mold or simply be so numerous that they give your roof a grimy appearance.

Maple trees are notorious for their sappiness. When you have a lot of tall maples in your yard, keep the trees pruned back as much as possible from the space over your roof. The fewer overhanging tree branches you have above your home, the less likely it is that sap will stain your roof.

Other trees that drop excess sap on roofs include the following:

  • Sugar, Norway, canyon, bigleaf, and rocky mountain maple
  • Black, red, and silver maple
  • Gorosoe
  • Butternut
  • Black and English walnut
  • Heartnut
  • Paper, river, yellow, black, gray, and European white birch

Avoid planting the above trees close to your home or driveway to keep sap from falling on your property. Contact your tree service to selectively prune tall tree limbs that hang over your roof if these trees are already growing on your property.

However, prune trees at the right time to avoid increases in sap production. Trees cut during the growing season produce an overabundance of sap to help protect the fresh wounds in the pruned areas. Hire your tree service to remove tall deciduous tree limbs when the trees are dormant (bare of leaves in winter) to reduce the likelihood of pruning-related sap issues.

Insect-Related Stains

Insect damage from trees is a big cause of sap-like stains on roofs. Large overhanging oak-tree limbs often drop a sap-like substance from their leaves that isn’t sap at all. The substance dribbling from the oak leaves is actually insect excrement.

Tiny oak leaf aphids feed on oak trees by drawing out all of the juice inside the leaves. Aphids then produce a sweet substance called honeydew from the plant matter. Honeydew is the aphid’s waste byproduct and makes up some of the material dripping from oak trees onto roofs.

Trees infested with aphid honeydew often develop additional diseases and infections. Aphid-infested oak trees produce more sap, so the trees can cover your roof with both sap and honeydew.
Pine bark beetles and other beetle species also cause roof staining from pine trees and other plants. The beetles lay their eggs beneath the bark of pines and other tree species. Hatching beetle larvae then drill holes in tree trunks. The infested pine trees respond by making extra sap to plug the beetle-larvae holes.

If your roof has any pest-related sap stains, schedule professional treatment for the infested trees. Tree-service experts have a variety of tools and products to fight beetle and aphid infestations of trees so your trees are healthier and stop making so much sap.

Gloeocapsa Magma

In humid areas with warm summers, stains and streaks often appear on asphalt shingles. Mold is sometimes to blame, but blue-green algae known as Gloeocapsa magma are often the true culprits responsible for ugly streaking and staining of roofs.

Gloeocapsa magma are tiny cyanobacteria that use light for photosynthesis and calcium carbonate particles for fuel. Common roofing shingles are made of limestone, which absorbs water and contains organic material the G. magma needs to thrive. Over time, G. magma encroachment causes shingles to age prematurely, rot, and lose surface granules.

Hire a roofing professional to clean the stains from your roof and apply algae-killing agents. Be aware that some of the products used to kill G. magma algae may be harmful to landscape plants. Prepare for the algae cleanup of your roof by deeply watering the soil and spraying water on all of the plants around the perimeter of your home.

To prevent regrowth of G. magma, hire your roofing professional to install copper or zinc strips under the shingle rows close to the peak of your roof. Zinc and copper kill algae growth from G. magma. Rainwater flows over the metal strips and washes over shingles, killing any forming patches of G. magma.

When replacing a roof in an area known for high rates of G. magma staining, choose a replacement roofing shingle embedded with copper granules. The copper granules are lethal to any G. magma growth, so your shingles look great without constant attention.

Get those nasty sap and algae stains off your roof by contacting The Roof Doctor today. We also install copper and zinc flashing and replacement roofs for clients throughout the Pacific Northwest.

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