Professional San Antonio roof cleaning that protects your roof

What causes black streaks and algae?

The dark streaks are usually Gloeocapsa magma, a cyanobacteria carried by wind. It thrives in warm, humid conditions, which describes a San Antonio summer well. The dark outer layer protects the algae from sunlight, which is why the streaks look black rather than green. Shaded slopes stay damp longest, so the streaks often start there and spread downhill with rain runoff. Our page on Algae & Black Streak Removal covers the details.

Moss, lichen and leaf debris

Live oak leaves, pollen and juniper needles collect in valleys, behind chimneys and along the lower edge of the roof. That layer holds water, and moss and lichen then take root in it. Moss can lift the edges of shingles and work between tiles, so it should be removed rather than left to grow.

How can you tell what is on your roof?

Look from the ground with binoculars, or check a photo taken from the yard. Dark vertical streaks point to algae. Green, thick, fuzzy patches point to moss. Crusty gray or green circles point to lichen. Granules in the gutters or downspout outlets point to shingle wear, which should be checked before any cleaning. Never climb onto a wet roof to inspect it.

Why does the cleaning method matter?

Asphalt shingles are coated with granules that shield the roof from sun. High pressure knocks those granules off and can push water under the shingles. Many manufacturers advise against pressure washing a roof. This is why Pressure Washing is used on driveways, patios and siding, while roofs get Soft Wash, which relies on a cleaning solution, a dwell time and a low-pressure rinse.

How does a soft wash work step by step?

The crew first wets plants and covers or moves delicate items. They then apply a mix of water, a cleaning agent and a surfactant that helps it cling to the roof. The solution sits for a short dwell time while it breaks down algae, moss and lichen at the root. Finally the roof is rinsed at low pressure from the top down so that dirty water runs off the edge and into the gutters. Rinsing the landscaping afterward is a normal part of the job.

How do roof materials differ?

Asphalt shingles are the most common roof on San Antonio homes and are the most sensitive to pressure. Clay and concrete tile are tougher on the surface but can crack if someone walks on them carelessly, so crews use soft shoes and plan each step. Metal roofs are smooth and clean easily, but they can scratch and slip when wet. Flat commercial roofs add ponding water and drain areas that need attention.

When is the best time to clean a roof?

Choose a dry, calm day. Very hot midday sun makes the solution dry too fast, and strong wind can carry spray onto cars and plants. Many owners schedule cleaning in spring or fall, after pollen and leaf drop, so that the roof starts the season clean.

How often should it be repeated?

It depends on shade and trees. A sunny roof may stay clean for years, while a roof under live oaks may need attention sooner. A quick look from the ground each season will tell you when the streaks are coming back.

What happens after the cleaning?

The cleaning solution keeps working after it is applied, so growth continues to fade over the following days and rain rinses the remaining residue. Results on Shingle Roof Cleaning and Tile Roof Cleaning are usually visible within days to weeks. Some homeowners add zinc or copper strips near the ridge, since rain carries trace metal ions down the roof that slow regrowth.

When is a roof cleaning not enough?

Cleaning cannot fix curled shingles, bare spots, cracked tile or active leaks. If you see missing granules, daylight in the attic or water stains on ceilings, have a roofer inspect the roof first.

Ask for a written quote that lists the roof material, the method and what is included. A quote that only says pressure washing for a shingle roof is a warning sign. Compare methods first, then compare prices. A very low price often means a rushed job or the wrong method.

Extra work such as gutter rinsing, moss treatment on tile or cleaning a detached garage roof can change the total, so ask what is included before you agree.

Ask how they plan to clean your roof. A good answer is soft wash at low pressure with a cleaning solution, not a pressure washer. For tile, ask how they will avoid walking on fragile pieces.

• A written quote that names the roof material and the method.
• Proof of liability insurance, since work at height is risky.
• A plan to protect plants, windows, air conditioning units and outdoor furniture.
• Clear steps for rinsing gutters and downspouts.

For hard surfaces such as patios, see Pressure Washing. For office and retail buildings, see Commercial Roof Cleaning.