How Safe Is It to Clean a Tile Roof with Bleach?


Roof cleaning is often performed by hired commercial contractors and with the help of various products including a solution of sodium hypochlorite, referred to as bleach. Despite the recommendations from the Asphalt Roofing Manufacturers Association (ARMA) to implement a 50/50 mix of water and chlorine bleach to remove the algae and moss, there have been a number of cases raised to the question of how safe it is to clean a tile roof with bleach.


Whether you have a tile or any other type of roof, the safe method to clean a roof is to avoid using bleach at all costs. Bleach-based cleaning products will speed up damage to the surface of the roof tiles. Additionally, it will produce runoff that harms the vegetation around the house. 


What’s more, bleaching a roof is a guaranteed long-term strategy. Basically, bleach products make the black mold stains or the roof algae translucent by bleaching them. Thus, they are not visible from the ground, that is until next year when you will be forced to repeat the roof washing process to make it look “clean” again.



Is Bleach Safe for Tile Roofs and Does It Cause Damage to Roof Tiles?

According to data issued by the Consumer Reports organization, the commonly implemented chlorine-bleach solution is NOT recommended due to the damaging effects it can cause to roof tiles. Chlorine is a toxic gas that has corrosive properties. A staggering number of contractors who utilize bleach (using the term “Soft Wash”) will often include phosphates as an additional ingredient to the mixture. Phosphates are well-known as a pollutant in most watershed locations.

Such additives have now been banned from household products in up to 16 states. Even in weak concentrations, chemicals such as trisodium phosphate (TSP) and bleach accelerate the damage of rooftops even when rinsed properly. What is more, chlorine bleach releases a toxic gas that contaminates everything around as it evaporates and when sprayed.

Bleach has been proven to be directly responsible for the corrosion of roof fixtures like boots, flashing, valleys, and tile roof underlayments.

Contractors often prefer to use the quick and easy bleaching method because it allows for the dark-colored stains to disappear with just a spray. There is no rinsing involved in the process. As a result, this is leaving the chemical to ooze into the tile shingles, eventually causing them to dry and crack. The runoff will lighten the colors of surfaces below the roof’s drip line. Also, any nearby plants and grass are getting destroyed as well during runoff.

Though not all contractors attempt to deceive customers, many will devise their own homemade formulas consisting of a variety of other chemicals such as dish and laundry detergent, surfactants, and odor masking scents. It is to hide the smell of the bleach that serves as the main ingredient of the formula.

Thus, it is recommended to only use non-bleach roof cleaning products that are approved for either cement or clay tiles with a spray and rinse to properly remove discoloration. Contractors may inform you that they are following ARMA recommendations but they might actually be planning to use sodium hypochlorite (which is commonly known as bleach). If they are going to water down, spray or cover vegetation, use a runoff recovery system, or mention “soft wash”, they are planning to use bleach.



What Are the Safest Chemicals to Clean Roof Tiles?

The vast majority of pressure washers come bundled in a detergent kit to use with high power equipment and low-pressure products like the concentrated Krud Kutter formula multi-purpose house wash that produce large quantities when mixed with water at an appropriate dilution rate. A single biodegradable, non-toxic gallon of Krud Kutter’s is capable of cleaning nearly 4,000 square feet alone. It will get into roof tile surfaces to lift out unwanted fungi and stains. Krud Kutter is also biodegradable and non-toxic to vegetation and animals.

Many biodegradable products such as Defy Roof Cleaner concentrate are suitable for roof cleaning as they are far less rough on the tiles. It is recognized as eco-friendly and non-pollutant due to its formulation of detergents in combination with sodium metasilicate with soda ash and sand. Diluting to a 6:1 ratio in one-gallon containers, the product is considered completely harmless to vegetation and rinses away easily with water.

Some professional roof cleaning contractors recommend using sodium hydroxide based products for tile roof cleaning. They not only act as an effective degreaser but are also considered environmentally friendly and safer roof washing method.

Although ceramic roof tiles are able to handle pressure washing at high levels, clay and concrete tiles are more porous which causes them to absorb used chemicals easily and damage them in the long run. In order to not damage the tiles’ cellular structure, it is recommended to wash them down with a gentle bleach or soap-based cleaning product. Then, cover them with a clear topcoat or sealer which smoothens the tile surface and hinders the excessive adherence of debris such as dirt, mud, bird droppings, and fungi. Additionally, such tiles can be rinsed off with clear water.

In essence, regardless of which cleaning solution you decide to use for washing your tile roof, you must check with the manufacturer of the roof and follow their guidelines. Using the mildest chemical possible is key to achieve desired results.


How Often Should a Tile Roof Be Cleaned?

There are many answers to the question of how often a tile roof has to be cleaned. Your roof’s current condition has a lot to do with its lifespan. So pay attention to your roof as this will help you save money in the long run.

Roof cleaning is a common process of removing unwanted debris from the top of houses including but not limited to moss, algae, mold, mildew, and lichen. Given the limited lifespan of any particular roof, the cleaning process extends the duration for which it can function. If your tile roof is regularly cleaned and properly cared for, it will last longer and highly improve your home’s appearance.

Any presence of biomass, soot, or dirt directly affects how much sunlight is absorbed by the roof and therefore the whole house. The buildup of the problematic debris typically forms on the western and northern parts of roofs and weaken the structure in these areas even more.

You should decide on what form of cleaning is necessary, depending on the type of roof you have. Additionally, the frequency of roof cleaning should also be based on other factors such as local weather conditions (e.g. high humidity), types and quantity of trees that surround the house, the roof’s age, and whether or not it has sustained prior damage.

Concrete tiles, which are most common, demand more frequent cleanings, usually every 2 to 3 years, depending on the form of cleaning. This is because the concrete tiles are brushed, barrel and flat, s-tile with a rough finish that takes an extended period of time to dry. However, new tile roofs typically require their first cleaning after 5 years. High pressure roof washing erodes the tile finish, therefore, even more regularly scheduled cleanings will be required.




What Is the Best Way to Clean a Tile Roof?

If you plan to clean your own roof, it is essential to take the appropriate safety precautions to avoid accidents and injury. Wear non-slip shoes with proper traction, safety glasses, and protective rubber gloves. Safety line and harness are also essential if your house is tall or for high pitched roofs with moss and algae build-ups.

A partner helping from the ground is highly recommended as they can pass the tools and materials up saving you climb the ladder frequently. Also, their alternative viewpoint allows them to observe the roof and help direct you as necessary. If this is not possible, you should consider hiring a professional as the job is quite dangerous even with all the necessary precautions. For such reasons, the majority of people prefer to take on the expense to ensure their own safety.

To start, carefully place a sturdy ladder against the wall near an area in which you plan to start cleaning. Begin on one side and work backwards to the other end to remain in the driest region possible and remove the need to walk on wet tiles.

When using a pressure washer, you can easily spray off any dirt, loose paint, mud, grime, mold, leaves, dead insects and small animals, and other objects from roof surfaces. It is critical to keep your hands, arms, legs, and feet away from it as the pressure is strong enough to remove flesh from bone. This water mechanical sprayer should be used at low pressure to blow away the unwanted debris from the highest peak of the roof down towards the gutters.

After allowing some time for the roof to dry, apply appropriate eco-friendly cleaning solutions like Roof Shampoo on the surface. Allow the solution to soak until dry. The rinsing process will depend largely on the extent of algae and other organic growths on the roof. If there is a high concentration of moss and mold, the chemicals should be allowed to seep in for a longer time. It needs to be repeated several times to fully remove stains and dirt.

Gutters are crucial for maintaining the roof in great shape during rainy weather and can become easily clogged when left unchecked. Removal of the debris with the same process helps to free up space.

Finally, buff and survey the roof to inspect for any damages and assess if there’s a need for any repairs.


In summary,

There are different chemicals and a multitude of methods being used to clean a tile roof, with pros and cons for each of them. In general, to avoid damaging the tile roof, it is recommended to implement low-pressure roof washing. Eco-friendly cleaning solutions that do not contain any form of bleach or TSP are the safest for roof tiles and for lowering environmental impact.