By Daniel Weadley
© DanielsRoof.com
Roof moss is unsightly, blocks both gutters/pipes and also leaves black marks on patio slabs and conservatory roof panels. It will gradually encroach over the entire roof and many homeowners prefer to have it removed. Once the moss is taken off, the old roof tiles will look much brighter and cleaner, even if no chemicals or pressure washers are used during the process.
This page explains how I remove roof moss and why I never use a high powered pressure washer (or any type of pressure washer).
Here you can find a list of moss killers, they are chemicals that are diluted with water and then applied to the roof (or patio) preventing regrowth. It is best to apply these after the moss has first been removed, if you spray the roof without first taking the moss off, the rain will wash all the dead moss into the gutters causing them to block up.
Will Moss Damage My Roof Tiles?
This is a good question and one I often hear, the answer is maybe but for most roof tiles it is most certainly unlikely. Although getting rid of the moss on your roof does has many other benefits. Most of my customers want the moss removed to either improve the appearance of the roof or because they are fed up with the blocked gutters and clumps of moss falling to the ground and sticking to the patio, car, conservatory roof etc.
Let me explain… First please ignore anything that any roof coating company has told you about the weight of moss causing structural stress on the roof or how a thin coating of sealant will add years to the life of the roof. In my opinion these are tactics often used by “hard sell” salesman and not professional roofing contractors.
Have you ever seen the “feet” that you place underneath plant pots in your garden? The purpose of those feet is to allow water in the pot to drain away, without them the pot will remain wet/damp and when the temperature drops below freezing in winter the pot will crack. Water has that effect on terracotta, clay and even concrete, especially thin concrete such as roof tiles.
Moss holds water, so by removing the moss from the roof you are reducing the possibility of tiles suffering from winter cracks. Moss also tends to grow on cement, so it can disturb the bond between ridge/apex tiles and the roof.
By itself moss wont damage the tiles and the biggest advantage of a moss removal project would be on the guttering. With less blockages they can work more efficiently and require much less maintenance. The chances of an expensive blockage in the underground drain are reduced and products such as gutter guards and down pipe filters will not clog up so quickly.
So is it Worth Removing Roof Moss? Is it Cost Effective?
If you have excess roof moss and you are concerned about the tiles never having the opportunity to dry out, then yes removing the moss and preventing regrowth with chemical moss killers is worth considering. If the growth is only mild then it may not be needed. It depends on whether you are fed up with constantly having to clear out the gutters or seeing clumps of moss on your lawn/patio etc.
Having the moss removed from the roof will improve the kerb appeal of the property but won’t increase it’s value. Excessive moss might be something that is highlighted on a survey as a potential issue but normal levels of growth shouldn’t cause any problems.
Moss on Clay Tiles
I never recommend climbing over a roof with clay tiles as they are so fragile and are more likely to break, using a pressure washer on these tiles really would create a flood risk! So if you have these tiles on your roof your options are very limited. The best option is to use a long reach pole with either a scraper or wire brush attached to the end and try to remove as much moss as possible without actually walking onto the tiles.
This work could be dangerous if done from a ladder but an access tower raised to gutter height would be perfect.
A chemical can then be sprayed onto the roof to kill off any bits that were missed and to prevent early regrowth. I have completed several projects like this and in my opinion it’s a safer option.
Concrete tiles are completely different, you can walk or rest a roof ladder on these and they rarely break.
Roof Coatings and Sealants
I would never recommend a roof tile sealant or coating. In my opinion they are products that have a short life expectancy. They usually wash or wear out after a few years and certainly don’t offer long term protection from moss let alone the elements. I try to think of these sealants as little more than expensive paint and in my opinion that is exactly what they are.
I also dislike the look of a freshly painted roof, most roofs that have been painted shiny red tend to look out of place next to neighbouring roofs that are well weathered.
I have seen many roof coating projects and while the roofs do look rejuvenated immediately after a fresh coat of “paint”, it isn’t long before they start to look patchy and in need of a re-coat.
Probably worth remembering this old saying:
Paint it once, be prepared to paint it twice.
Or, as we like to say in the trade:
If it doesn’t need painting, don’t paint it.
Look at the Photo Below
The photo below is of a roof with 30 year old tiles, for the last 25 years they have been absolutely covered in moss growth, after scraping the moss off I couldn’t find any problems with the tiles whatsoever. They were in excellent condition. This is quite normal.
If there is already a problem with the roof, such as loose cement or roof tiles with cracks in them then obviously moss growth is only going to make things worse as the roots can widen cracks and disturb already loose cement. By itself though, moss doesn’t directly cause any major roof issues.
If you have a roof with cracked tiles or loose cement then the best approach would be to fix those issues rather than applying a coating, in my opinion.
By the way – I didn’t use a pressure washer to remove the moss you see in the photo below. Check out my page on how I remove roof moss to learn more. Here is a list of tried and trusted moss killer chemicals I have previously used.
