what causes moss to grow on roof tiles?

Question

I have just been up clearing my gutters out and I noticed that there is a lot of moss growing on my roof tiles, particularly in the overlaps, what causes this and short of having my whole roof re-tiled is there anything that can be done to remove the moss and more importantly keep it from growing back?

Answer 1

Ever see the "feet" that you place underneath plant pots in your garden? The purpose of those feet is to allow water 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.



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 desirable. 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.



Tips for roof moss removal:

Use the correct access equipment - safety first

Carry out this type of work when the roof is dry

Start from the top of the roof and work downwards using a trowel to scrape off the moss

Using a stiff broom sweep off any loose moss and dust

Replace any broken tiles and clear out gutters

Check condition of cement work and repair as required

Spray roof with a fungicide moss killer to kill off any roots and prevent early re-growth

Should I use a pressure washer?



Using a pressure washer is one way of removing the moss along with any other dirt and grime. However if you have broken tiles on the roof then there is a flood risk and old tiles can suffer from discolouration as the loose grit on the tile surface is blasted away. Most professional roofing companies tend to stay away from using pressure washers, so that just leaves the cowboys and questionable firms.



Moss will probably not damage the roof. Moss tends to grow on the surface of the tile feeding on minerals and grime that collects on the tiles. In most cases moss will not damage the tiles, however there will always be corner cases and older tiles are more likely to suffer problems.

Answer 2

Moss Growing On Roof

Answer 3

not quite. Zinc would be a better metal to use. Older homes, have less moss growth because they tend to have steeply pitched roof slopes. Rain runs off such a roof quickly and the tiles dry faster. Moss needs moisture to thrive and a dry roof simply doesn't provide this important condition for growth. Roofs on more modern homes are generally pitched at shallower angles - offering suitable growing conditions for mosses and lichens. It is also worth pointing out that shade from overhanging trees will encourage moss growth on a roof of any pitch. Moss may also be getting a boost from acid rain. Just as it needs water to grow, moss requires an acidic soil or growing medium. Acid rainfall can provide this condition in soil, and on roofs. There is also an increase in mossy conditions in lawns recently and says this also may be a result of acid rain. Moss can shorten the life of a flat roof by holding moisture against the asphalt, however, is not a problem on a tiled roof. The best way to get rid of moss that already has a toehold is probably to spray it with a commercial chemical. After the moss dies, it should be removed from the roof, if possible, to avoid a regrowth. Pressure washing and a light brushing can assist in this removal process, but you need to be careful not to damage the roof while cleaning it. Zinc strips that come in coils 50 or so feet long, and several inches wide. You position close to apex of the roof, leaving two inches of the metal exposed, nail it in place. They need to be placed every 15 feet up from the bottom to protect the whole roof and then nature does the rest. Rain and snow melts dissolve some of the zinc and send it down the roof where it apparently kills moss and fungus. One option is to install a metal roof. Moss is not able to grow on the smooth surface. The pesticide products most commonly sold for moss control contain zinc sulfate. Zinc, while a naturally occurring mineral and an essential micronutrient in humans and plants, is toxic at higher exposures. Concentrations as low as 10 parts per billion can kill fish. Zinc sulfate is highly water soluble and while it kills moss, it won't remove the plant material from the roof. If there's a significant amount of moss on your roof, you would still need to clean the roof following the use of the zinc sulfate product. Simply cleaning the roof, without using the pesticide, is less work and more environmentally-friendly process. Strips of metallic zinc roughly three inches wide are a better method. Rain runs across the zinc strips and a small amount of zinc dissolves in the rainwater as zinc carbonate. The strips have the advantage that they are long-lasting and release only a small amount of zinc into the environment at any one time.

Answer 4

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what causes moss to grow on roof tiles?

I have just been up clearing my gutters out and I noticed that there is a lot of moss growing on my roof tiles, particularly in the overlaps, what causes this and short of having my whole roof re-tiled is there anything that can be done to remove the moss and more importantly keep it from growing...