You can use a product called 30 seconds roof treatment to kill the moss and lichen prior to the roof being cleaned.
How to remove lichen from terracotta roof tiles.
Terracotta tiles are made from natural clay which is a naturally moist material.
Older terracotta roof tiles will become brittle over time and if so should not be cleaned as the tiles may break underfoot and water can.
Mould when mould is growing on top of your roof it is often indicative of problems that started within the home.
Lichen is a hardy growth known to firmly.
Lichen avoids galvanized steel copper and zinc because these metals work as a natural biocide.
Removing lichen fully using this method is nearly impossible not to mention time consuming especially if you are dealing with a large surface like a roof.
You also risk the potential of accidentally damaging the protective top layer of your roof shingles while trying to remove it with this method.
Moss itself is a plant while lichen conisist of a fungus and a photosyntheizing plant living together.
For best results mix the wet forget and spot spray the lichen leave for 10 15 minutes and then respray the lichen and the entire roof to ensure the lichen absorbs the wet forget thoroughly.
If any members of your family are susceptible to allergies or respiratory conditions it is even more important to regularly clean your roof tiles.
Remove moss and lichen from your roof with vinegar.
As you did in the previous step walk backwards when you are spraying away from the wet tiles and onto the dry ones.
Terracotta roof tiles are typically cleaned to have the visible moss and lichen removed.
This will remove all the moss and lichen as well as any built up dirt.
Moss and lichen is attracted to the roof tiles surface and if left will continue to grow and most likely restrict the flow of rain water over the tiles surface into the roofs.
Give the anti moss spray time to do its job and then use the high pressure cleaner to wash the tiles down.
For an average 3 bedroom tile roof with lichen you would require 3 x 5 litre packs depending on the total area covered with lichen.
Mould algae lichen and moss that is growing on your roof tiles can transfer into your roof cavity and be circulated in airflow throughout your house.
This will remove the unwanted moss lichen and mould that has embedded into your tiles.
Lichen on terracotta roof tiles is particularly unappealing to the eye and is best handled before it has a chance to cake in and ruin the tiles.