Black Streaks on Gutters in Florida: What They Are and How to Remove Them

Three things combine:

On many Florida homes the roof itself grows dark streaks from algae, and the runoff transfers them to the gutter below.

• Runoff carrying dirt and algae from the roof over the gutter lip and down the face
• Humidity and shade, which encourage algae growth
• Oxidation on older or lighter finishes, which leaves a chalky, dull surface that holds dirt

Not usually. The streaks are surface staining, and they do not weaken aluminum. They can make a house look neglected, and heavy algae can hold moisture against the finish. If the gutter is also sagging or leaking, address that separately.

Use the gentlest method that works:

A professional exterior cleaning uses a low-pressure wash and a cleaner made for the finish. See gutter brightening.

• Soft brush or sponge with a gutter-safe or mild cleaner and water
• Rinse thoroughly so cleaner does not stain the wall or kill plants
• Test a hidden spot first to make sure the finish is not affected
• Avoid high pressure, which can strip a baked-on finish
• Avoid harsh abrasives that scratch the coating

• Keep gutters clean. Overflow carries dirt down the face.
• Treat roof algae if it is the source, using methods suited to your roof type
• Trim branches that shade and drip onto the roof
• Schedule an annual exterior wash for the shaded sides

Exterior cleaning typically runs $120 to $350 depending on linear feet and stories, and it is often cheaper bundled with an interior cleaning. See gutter cleaning cost in Orlando.

Heavily oxidized finishes, where the coating has chalked, may only improve. If the finish is peeling or the metal is pitted, replacement or repainting may be the answer. Do not replace gutters just for streaks.

The University of Florida IFAS Extension has information on algae and moisture on Florida homes, and the National Roofing Contractors Association publishes general roofing guidance.

The north and east sides get less sun and stay damp longer, so algae grows faster there. Gutters under trees see more debris and more staining. Homes with roofs that have algae streaks send that growth down onto the gutters. If one side of your house is worse than the others, look at shade, tree cover, and the roof above.

If you are unsure what finish you have, test in an inconspicuous spot or ask a pro.

• Baked-on enamel on aluminum cleans well with gentle methods.
• Older painted finishes may chalk, and heavy scrubbing can dull them.
• Copper weathers on its own and should not be cleaned with harsh products.
• Steel may rust, which cleaning will not remove.

A ladder, a soft brush, a bucket, and a mild cleaner are enough for a first-floor gutter. Use a ladder stabilizer, wear eye protection, and rinse the cleaner from plants and walls. Do not mix chemicals. For two-story homes, hiring out is safer. See gutter cleaning cost in Orlando and how often to clean gutters in Florida for context.

Exterior gutter cleaning typically runs $120 to $350, and it is often cheaper as an add-on to an interior cleaning. Spring is a good time, after pollen season and before the wet season. Fall is another option, before the drier months. Ask whether the price includes downspouts, since those streak too.

In shaded, humid areas, streaks can return within a year. Many owners clean the shady sides annually and the sunny sides every two to three years. If you clean the roof or treat algae, timing the gutter cleaning afterward makes the results last longer.