EVERYTHING YOU NEED TO KNOW ABOUT ROOF MOSS
By an expert
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I used to work as a roofing contractor, and roof moss removal was a service I offered, it was both very effective and popular and I was once so busy with work, I had to turn down customers.
On many roofs, moss can be troublesome; I’ve seen it block gutters, rainwater pipes and even clog up underground drainage soakaways.
Patios, conservatory roofs and paths underneath the roof can also be covered in bits of moss that have been blown off the roof.
In extreme circumstances, I’ve also seen it eat away at the surface of roof tiles, where it accelerated the weathering process.
But how much does it cost to remove roof moss? Is manual moss removal better than pressure washing?
Keep reading to explore my price guide and discover answers to common questions, which are based on my 18 years of experience.
Note: The price guide on this page is for manual removal of roof moss, this type of project is completed with hand tools and brushes. To see my guide to roof power washing, check out this roof cleaning price guide.
My Roof Moss Before and After Photos
The photos below were taken by me and show what a difference manual roof moss removal can make to the appearance of a roof.
I removed the moss with a scraper and brush, nothing else.
(Click to expand)
Typical Works Schedule For Roof Moss Removal
Here’s a works schedule for roof moss removal, it’s very similar to the ones I sent out to customers when I offered moss removal services:
- Raise platform access towers to the roof edge (this provides edge protection for workers on the roof).
- Remove roof moss by way of scraping and brushing.
- Sweep down the roof to remove dust.
- Check the roof for cracked and broken tiles, replace them where needed.
- Clear out gutters and clean exterior of gutters.
- Check rainwater pipes to ground level and unblock them as required.
- Spray the roof tiles with a fungicide treatment to kill off any moss spores, which will deter the moss from growing back.
- Lower the access platforms and take away all waste.
I Asked 34 Firms to Provide a Price For Roof Moss Removal
I consider myself an expert as I’ve removed moss from dozens and dozens of roofs, but I left the roofing industry over 10 years ago, and I wasn’t sure how much others are currently charging, so I asked 34 roofing firms from various locations around the UK how much they charge.
I emailed them photos of a roof 8 metres long which had two sides; front and rear.
The figures below are an average of the prices I received:
|Location:||Price inc VAT:|
|London and South||£1000 - £1250|
|Midlands and North||£750 - £950|
How to Stop The Moss From Growing Back – My Experience
Moss is spread by microscopic spores, and I’ve seen them grow incredibly fast when they were exposed to moisture.
They’re usually spread by the wind and they seem to prefer shady damp areas, such as behind chimneys, on north-facing roofs and tiles located under trees.
Unless a fungicide is applied to the roof, these tiny spores from the removed moss will quickly start sprouting into new clumps of moss.
I have seen roofs demossed, only for the moss to regrow in a matter of months.
In my opinion and based on my experience, the roof must be thoroughly treated with a fungicide and enough of it to get into the tile overlaps.
Through years of testing and experimenting, I found that the best fungicide for this is Benzalkonium Chloride, a chemical that’s widely used to prevent mould, moss and algae growth on surfaces. I’ve used this chemical hundreds of times, and it works brilliantly at preventing moss from growing. I’ve even used on patios, driveways, walls, and many other hard surfaces where moss and algae were a problem.
What Happens if the Fungicide Isn’t Applied?
From my first-hand experience – the spores will start to grow as soon as they get wet, small sprouts of moss may form in a matter of weeks, especially if it’s winter.
More widespread moss growth will form in months, first on shaded parts of the roof and then spreading to all other areas. Within 1 to 3 years, the roof will be covered in moss again.
I cannot emphasise how important the moss treatment is – moss produces millions of spores and they need to be treated.
How Long is the Fungicide Effective For?
Once the roof is demossed and treated with a fungicide, the moss shouldn’t grow back for several years.
On south-facing, sunny parts of the roof, I’ve seen the moss take 5+ years to take hold.
On damp, north-facing parts of the roof, I’ve seen the moss will grow back sooner, you can expect small amounts within two to three years and more prolific growth in 3-5 years.
How to Permanently Stop The Moss Growing Back?
Despite some firms advertising expensive roof paints, coatings, sealants and elixirs that apparently stop moss growing, there is only one solution that I feel is 100% effective, and it doesn’t involve any costly products.
Remove the moss once, treat the roof with a fungicide and reapply the fungicide every few years.
If the fungicide is reapplied before the moss can take hold, it can be kept in check perpetually – this was a service I offered for my customers, and many of them would have me back every few years where I would clear out any leaves from their roof gutters and respray the tiles with the fungicide. This service took no more than a couple of hours on a typical roof, was effective and popular.
Nowadays, roofers and cleaners have long-reach poles, meaning they won’t even need to step foot on the roof after the initial moss removal (see photo below). This reduces the cost of re-treatment considerably:
The fungicide can be reapplied periodically to prevent the moss from growing back
Extra Costs to Consider
The prices on this page are for a straightforward moss removal project.
I’ve worked on enough roofs to know that there are always projects that cost more.
You need to pay extra for:
Access Equipment – I’ve included the cost of access equipment in the form of tower platforms or other similar access. However, some roofs may require a full scaffold system which would cost extra. If your roof is more than three or four storeys high, has a large conservatory underneath it or is otherwise difficult to access, the moss removal project will cost more. Based on my experience, the scaffold can sometimes cost more than the project itself.
More Substantial Repairs – When removing roof moss, contractors should check the roof for broken tiles and swap them for new ones – I always did this and every roofing firm I know did as well. More substantial repairs, such as replacing a roof valley, must be priced separately.
Roof Size – The prices on this page are for an “up and over” roof, that you would typically find above a three-bed home. Larger roofs or those of a more complex design will take longer to clear moss and cost more.
Tile Type – Moss can be removed from any roofing tile, and most roofs in the UK are covered with concrete tiles, these are tough and difficult to damage. However, I often found it difficult to demoss clay tiles as they’re more fragile, and I sometimes had to hire specialist access equipment such as a cherry picker or scaffold hire, and this added to the cost.
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I hope you found my guide to roof moss removal insightful.
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Roof Moss FAQs
Why Can't The Fungicide Be Used to Remove the Moss?
The fungicide I recommend can kill the roof moss but the moss would still be on the roof. It could take months, maybe years, for the dead moss to decay. Rainwater would then wash it into the gutters, rainwater pipes and possibly the drainage soakaways where it would cause blockages.
The fungicide should be used as a surface biocide to clear the roof of spores once the bulk of the moss has been removed and disposed of.
I've Been Told That a Roof Coating, Paint or Sealant Will Stop Moss. Is This True?
Roof coatings and sealants can slow down the growth rate of moss that’s on the tile surface, but it won’t stop moss from growing in the gaps and overlaps between the tiles.
I took this close-up photo and it shows moss growing between the tiles; no amount of paint or sealant etc will stop this:
If you want to know how much roof coatings cost, check out this page.
Why Can't This Type of Work Be Done From Ladders?
The Health and Safety Executive’s rules for working at height are crystal clear; any worker who spends more than a few minutes on a roof must ensure there is adequate edge protection in place to prevent falls.
Can The Roof Be Coated or Sealed After The Moss Has Been Removed?
Paints, coatings and sealants should only be applied to surfaces that have been thoroughly cleaned. The surface should not contain any dust, contaminants or pollutants etc. that could prevent the product from adhering to the tiles correctly.
The only way to thoroughly clean roof tiles to this degree would be by pressure washing them.
Demossing with a scraper and brush wouldn’t suffice.
I have seen contractors paint roof tiles without first sanitising the surface; the end result was horrendous as the paint peeled off in places.
Can Moss Be Removed From a Flat Roof?
Extra care will be needed when working on a flat roof as they’re more fragile than concrete tiles. In my opinion, moss shouldn’t be scraped or power washed off a flat roof.
I have brushed moss off a flat roof before without issue, but whether you can achieve this depends on the age and condition of the roof.
I've Been Given a Quote That is Considerably Higher/Lower Than The Figures on This Page. What Gives?
The prices I’ve displayed on this page are for a two-sided roof above a three-bed home, they are a rounded average of prices given to me by 34 roofing firms – not just my opinion.
If your price is significantly below this average, you may want to ask the roofer if they will be erecting edge protection. It’s not uncommon for roofers to complete this type of work from ladders even though they would be breaking the law. Some just walk on the roof with no protection whatsoever.
If the prices you’ve been given are much higher than our average price, it could be that you’ve sourced prices from a firm that has more overheads and needs to charge more. In general, the bigger the firm, the more they need to charge to make a profit.
I recommend sourcing at least three quotes from reputable roofers and comparing their work schedule and price to the information on this page.
Where Can I Find a Good Roofer?
The National Federation of Roofing Contractors and the Confederation of Roofing Contractors are well-known organisations that maintain databases of approved roofing contractors in the UK. The Competent Roofer scheme promotes roofers that agree to adhere to a high set of standards.
I’ve also partnered with Bark – one of the best places online for finding vetted, reviewed and rated tradespeople.
How Long Does it Take to Remove Roof Moss?
For a straight-forward up-and-over roof, two workers should be able to complete the project in around a day, perhaps a day and a half. This includes the erecting and dismantling of edge protection towers.
For larger roofs, perhaps with three or four sides, the work will take between 2 and 4 days, but in my experience, it really depends on the size, steepness and condition of the roof. The largest roof I ever worked on took myself and a colleague 6 days to complete but we did most in 2-4 days.
Extra time should be allowed for garages, porches, or roofs that are difficult to access.
Does Moss Damage Roof Tiles?
I’ve never seen roof moss destroy a roof tile or eat all the way through it, but it can cause light damage to the surface.
The vast majority of roofs in the UK are covered with concrete tiles, and for the most part, I’ve found these are strong enough to prevent any significant damage from moss.
In extreme circumstances, for example, when the roof is carpeted in moss, it may eat away at the surface, which essentially accelerates the weathering process.
I’ve found that on more fragile clay tiles, the extra moisture held by the moss will lead to an increased risk of damage in winter due to the freeze/thaw process.
While wet moss is heavy, the weight never threatens the structural integrity of the roof as it’s spread thinly, I have never seen a roof collapse or suffer structural damage from moss.
What is the Best Way to Remove Roof Moss?
If your goal is to remove the roof moss and stop it from coming back, then either manual or power washing techniques will suffice.
If you need the roof to be cleaned rather than just demossed, perhaps because you want to apply a roof sealant or coating, then it must be power washed.
I’ve removed moss from dozens of roofs manually and it’s a perfectly acceptable way to get rid of the moss.
What Are The White Marks on Roof Tiles?
White marks on roof tiles are lichen, a slow-growing thin organism that’s very tough to remove.
I found that the best way to remove them is by power washing or by treatment with a fungicide.
The fungicide requires time to work, and in my experience 4-6 weeks after the application, most of the lichen should’ve disappeared.
I do not recommend trying to remove lichen with scrapers or wire brushes as they will scratch and scuff the tiles, I’ve seen this several times and the scuffs leave the roof looking unsightly.
I spent over 18 years working in home improvement and later, the construction industry, this incuded 10 years as a roofing contractor.
My role encompassed many aspects of roofing, including repairs, roof moss removal and cleaning.
The photos on this page were taken by me and the advice offered is based on my experience.
The price guide I published is based on feedback from a selection of firms I randomly contacted, please bear in mind that every project is different, hence why I recommend getting at least three quotes.
More From Daniel Woodley:
Daniel has over 18 years of experience in construction, home improvement, and landscape garden industries and is a keen gardener.
He has hands-on experience in several fields and has worked as a cost estimator for several years.
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