As mentioned in a previous post, pressure washers can damage roof tiles, shorten roof life expectancy and cause flooding of the loft space.
Read more about why pressure washing a roof is a stupid thing to do
There is a way to clean a roof and it doesn’t involve any water at all.
It does involve some graft, some chemicals and a good dose of patience!
Remove the Moss and Apply the Right Chemicals
The most gentle yet effective way to remove roof moss is by way of scraping. A normal 9″ trowel should do it, if you choose a dry day any moss will flake off the roof much easier. This approach may involve some grafting and for a large roof you may even get the odd blister!
But… With scraping there is no damage to the tiles and no flood risk.
Look at the photo below, the moss was removed with nothing more than a trowel and a hand brush, the difference compared to the mossy section of roof is striking.
This photo was even taken before any chemicals were applied – what a difference!
So Why Use Chemicals?
If you apply a fungicide/moss killer after the moss has been scraped off, it will soak into the tile and more importantly into the overlaps of the tiles and kill off any tiny moss spores.
This prevents the moss from growing back really quickly.
As a bonus, this chemical will also kill lichen, so those black marks on the tiles will fade away a few weeks after the treatment.
No Pressure Washing. No Flood Risk. No Expensive (and Useless) Roof Coatings
As stated in other pages, roof coatings are often an expensive and short term approach to roof renovation. There is a real flood risk, the coatings often look terrible after a few years and they being mis-sold by many many companies in the United Kingdom.
The manual approach to removing moss and applying a chemical maybe considered an old fashioned approach but it is time proven, won’t damage the tiles and you certainly won’t have to worry about paint peeling off the tiles.
Did I mention that manually removing the moss/applying a fungicide is also the cheapest method?
Expect to pay around £500 for a semi detached house in Southern England. Compare that to £2000 for a roof coating.
How Long Does the Moss Killer Last?
Assuming that the roof isn’t under tree cover, the moss shouldn’t grow back for about 3 years, after 4 years there will be light growth.
For this reason, the homeowner should re-apply the chemical every 3 years, thus preventing any moss growth.
Moss killing chemicals are not expensive, expect to pay around £30 for enough to treat a semi detached property. A backpack sprayer costs around £25 and the work takes around an hour.
If you purchase a more expensive backpack sprayer (Hozelock 12 or 16 litre) then you will find they have a very long reach, about 6 metres! That is enough to reach the top of the roof from a ladder resting on the gutter. So once the moss is initially removed you wouldn’t even need to get on the roof again. The chemical can be applied from gutter height.
This type of work is often carried out by roof contractors, not the ones that paint roofs but traditional roofing companies.
You can indeed clean a roof without pressure washing, but the chemicals do take a little time to work.
Can a Moss Killer be Applied Before the Moss is Removed?
This is a common question, can/should a moss killing chemical be applied to the roof before the moss is removed?
The answer is no.
First, you would need much more of the chemical as the moss would soak it up.
Second, thick layers of moss will prevent the chemical from soaking into the tile/overlaps.
Third, if you were thinking of applying the chemical instead of manually removing the moss with a scraper (lazy you!) then you would have a big problem – the dead moss would gradually wash down into the gutters and block them. It could take months of heavy rain to wash all that moss off the roof. Your gutters would need frequent cleaning and even then they are still likely to become blocked.
What Chemicals are Best?
Try any of the moss killers listed here, they can be used on tiles, patios and driveways etc. I have used all of them previously.
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