Do new roofs need cleaning?

A roof starts collecting what grows on it from the day it is finished, and the documents that describe that process say nothing about how old the roof is.

TRI Alliance writes that mildew, algae and moss do not grow on the tile itself but on the dust and other organic material that settles on it, and that spores start to grow once there have been enough cycles of heat, moisture and light. Nothing in that description depends on the age of the tile, so the conditions TRI Alliance names can begin once dust has settled and the weather has run through enough warm, wet cycles.

ARMA's technical bulletin supplies the other half. It says the algae species involved “are transported through the air and tend to collect and grow on roofing structures and other outdoor surfaces,” that growth occurs “to varying degrees” in all regions of the U.S. and southern Canada, “especially those subjected to warm, humid conditions,” and that roof algae discoloration is most widespread in the Gulf States and along the Northwest and Eastern Seaboards. Spores carried on the air do not wait for a roof to age before they land. What the dark streaks are is explained on the black streaks on a Naples roof, and the causes behind them one by one on why a roof has black streaks.

That is why age does not settle the question. No roofing maker or association read for this page publishes a minimum age for a first cleaning or a rule that a new roof must not be cleaned, and nothing in their descriptions of growth treats a new roof as a separate case. A newer roof needs cleaning in the same circumstance an older one does: when growth has taken hold and shows.

The documents describe a roof's need for cleaning in terms of what shows on it, and they set apart one deposit, efflorescence, that is not growth at all.

• Small spots first. ARMA's prevention bulletin says algae discoloration typically begins as small spots before it turns into streaks on the roof plane.
• Streaks that are older than they look. The same bulletin says that by the time algae is visible it has likely been present for several months or longer, so the growth behind streaks on a newer roof has likely been there a while.
• Significant discoloration. Eagle Roofing Products' spring article gives its own trigger: “If you notice significant discoloration on your roof, you may want to consider having your roof cleaned by a professional.”
• Efflorescence on concrete tile. TRI Alliance and Eagle describe it as a deposit, not growth: TRI calls it a temporary surface condition, an overall chalky white bloom or concentrated patches, that carbon dioxide and rainwater gradually remove in most cases, and Eagle says the light patterning it leaves on darker tiles disappears completely after additional exposure to rain.

Efflorescence is a deposit from the cement, and the documents leave its removal to the weather. Even so, a white haze on a particular roof is not identified from a list: TRI Alliance's guide also has slurry-coated tile oxidizing and turning chalky, so naming a haze on a given roof is a roofing contractor's job. How the first months after installation play out, and where the installer's warranty fits, is answered on how soon a new roof can be cleaned.

Once growth is removed, TRI Alliance's line is that if it returns, treatment can be repeated as necessary: a statement about recurrence, not a schedule. Why growth comes back on a roof cleaned not long ago is answered on why a roof is dirty again after a year, and whether growth left in place for years comes off completely on removing old tile stains. TRI Alliance's other early-years number, an inspection two years after installation, is an inspection interval and never a cleaning date.

Some new shingle roofs are sold as resisting algae, and their owners can fairly wonder whether cleaning ever enters the picture. The claims belong to the makers, so they are quoted as the makers wrote them.

ARMA's technical bulletin describes algae-resistant shingles as asphalt roofing products “specifically designed to inhibit algae growth for extended periods of time.” GAF's current Technical Advisory Bulletin TAB-R-102, dated 9/19/2024, names its own version, shingles containing GAF Time-Release Algae-Fighting Technology, and says: “This proprietary technology is engineered with thousands of microsites that release algae-fighting copper over time.” Neither document gives a number of years, and neither says a roof built with those shingles will never show growth.

Those are product claims made when a roof is chosen, a re-roof decision for the owner and a roofing contractor. Whether they are worth weighing in Florida is taken up on whether algae-resistant shingles are worth it in Florida. Tile carries no equivalent claim in the documents read here.

A cleaning sits on the other side of that line. It removes growth and staining when they show; it is not a coating, and it is not represented as protecting a roof. Where a soft wash stops draws that boundary, which is why an honest answer to this question never describes a first cleaning as looking after a new roof.