Removing moss from a tile roof – how to succeed

Regular maintenance keeps a tile roof in good condition and ensures its longevity. One of the most important maintenance tasks is removing moss from a tile roof. In this article, we’ll explain how you can remove moss from a tile roof yourself.

Tile roofing is an ancient building method with a long tradition in Finnish construction as well. The first clay tile roofs were built as early as the 16th century. Today, about a quarter of roofs are tile roofs, although nowadays roof tiles are made primarily from concrete rather than clay.

The popularity of tile roofs is based on at least three factors:

1. A tile roof is long-lasting. When properly maintained, a tile roof can last up to 60–70 years.
2. A tile roof is quiet. It effectively insulates against the patter of rain, for example, which increases living comfort.
3. A tile roof is pleasing to many eyes and fits naturally into the surrounding landscape.

Why is removing moss from a tile roof important?

When roof tiles come from the factory, they have a coating that protects the tile from dirt and moisture. Over time, however, the coating wears away, exposing the bare tile. Unprotected stone collects moisture and gradually begins to grow moss.

Moss itself is harmless to both the roof and the house’s occupants. The problem with moss, however, is that it binds much more water and for considerably longer than the tile alone.

When the temperature then fluctuates around freezing, the water in the tile expands and contracts. This causes frost damage—small cracks in the tile—which gradually begins to break down the tile.

If left completely untreated, a tile roof will begin to crumble at around 30 years of age, at which point the only sensible option is a roof renovation. But don’t worry—next we’ll explain how to effectively avoid this scenario.

Removing moss from a tile roof yourself

Mosses are spore plants that thrive especially in moist and shady conditions.

Because moss has no roots at all, it must absorb water through all its plant parts—leaves, stem, and the small attachment rhizoids used for anchoring. This is why moss is such an effective moisture collector and, consequently, an unwelcome resident on a tile roof.

There are mainly two options for removing moss: moss remover and mechanical washing. If the goal is simply to remove moss and achieve a clean, moss-free appearance for the roof for a few years, the easiest method is to use a moss remover.

Before applying moss remover, the roof should be brushed clean of leaves and other debris as well as loose moss.

Hardware stores offer a wide range of moss removers from different manufacturers; good options include, for example, Sokeva’s BioComb products or Tikkurila’s Kilpi Roof Cleaner.

Moss remover is a powerful pesticide that destroys the moss growth entirely. However, it will also destroy other vegetation it comes into contact with, so it’s a good idea to protect the area around the house if there are plants you want to preserve. Protecting any edible plants is especially important.

Before applying moss remover, the roof should be brushed clean of leaves and other debris as well as loose moss. After this, it’s also worth emptying the gutters of any dislodged plant debris.

Next, the diluted moss remover is applied evenly across the entire roof, for example with a low-pressure sprayer. The roof must be dry during application and preferably for several hours afterward, so the product can work as effectively as possible on the tile roof’s moss growth.

The moss remover is not rinsed off but left to work on the roof. The remover and the moss debris it loosens will come down with the rain.

This doesn’t happen instantly but can take several weeks, even months, before all the moss is gone.

Is simply removing moss from the roof enough?

Simply removing moss from a tile roof is, in the long term, an insufficient method for sustainable tile roof maintenance. It does help the roof dry faster, but even more important is ensuring the tile roof has an intact protective coating.

Coating application can be ordered from a professional or done yourself if desired: for example, Tikkurila offers Kilpi Tile Roof Paint suitable for this purpose.

Removing moss from a tile roof in connection with coating

When a tile roof is coated after moss removal, the best method for cleaning the roof is a pressure washer. If the roof is not being coated, a pressure washer should not be used for cleaning, as it wears down the tiles’ coating significantly.

What’s important in washing is sufficient pressure and a generous amount of water. In a standard electric pressure washer, both are too low, so the best option is a powerful three-phase or gasoline-powered washer. These are available from many equipment rental companies. In addition to a powerful washer, no detergents or other tools are needed for actually washing the tile roof.

Because moss is extremely prone to spreading, it’s important to remove even the smallest plant parts from the roof before applying the paint coating.

Before starting the wash, it’s worth checking that the roof’s eaves and seams are intact and that water can flow freely through them. During washing, it’s also good to check the attic space to ensure there are no leaks in the underlayment. This prevents wash water from getting into the wrong place and causing unpleasant surprises.

When washing with a pressure washer, the most important thing to remember is that washing should always be directed from the roof ridge downward. Never the other way around, to prevent water from being forced under the tiles into the underlayment.

During washing, you may also find broken tiles on the roof, which should be replaced with new ones as they’re discovered. When washing is complete, empty the gutters of any dislodged plant debris.

Because moss is extremely prone to spreading, it’s important to remove even the smallest plant parts from the roof before applying the paint coating. This is most easily done with moss remover, which also destroys plant parts that have worked their way between the tiles.

Moss remover is applied to the dried roof and allowed to work for about a day before painting the tile roof. Moss remover designed for this purpose does not need to be rinsed off but can remain on the roof under the paint coating.

A house roof after tile roof coating by Väriset.

What should be considered when maintaining a tile roof?

Maintaining a tile roof is important and, as explained above, can also be done yourself. However, a few essential points should be taken into account.

1. Work safety. The most important thing when working on a roof is ensuring work safety. Even a gently sloped tile roof is slippery when wet, and moss, algae, and other growth make it even more slippery. That’s why a harness is absolutely essential when moving around on a tile roof.
2. Moving on a tile roof. A careless step can easily break a tile. Especially when moving on a tile roof in any state of disrepair, you should always step on the end of the tile, not the middle.
3. Protection. Plants you want to preserve must be protected from moss remover. In addition, especially when washing with a pressure washer and applying paint coating, it’s good to also protect the house’s walls and windows. The person performing the work must also have adequate protective equipment, including sturdy shoes, covering clothing, gloves, and safety glasses.
4. Avoiding water damage. When planning roof washing, the underlayment must always be checked extremely carefully first, as some water will always reach the underlayment during washing. The underlayment’s function is to support the roof covering and serve as a final safeguard to prevent water from reaching the attic insulation. Especially the penetrations in the roof (ventilation pipes, exhaust pipes, chimneys, etc.) should be reviewed and checked to ensure the underlayment is installed correctly around them.

Are you unsure about your tile roof’s condition?

If you’re uncertain about your tile roof’s condition or what actions it needs, remember that you can always request Väriset’s experts for an assessment visit. The assessment visit is completely free for you and doesn’t obligate you to anything, but you’ll receive important information about your tile roof’s condition as well as a fixed quote for any potential work.

Watch the video to see how smoothly tile roof coating goes with a professional: