Soft washed roofs: How long will they stay clean?

March 03, 2022

Soft washed roofs- How long will they stay clean?

Because of the many variable factors, it's impossible to give an exact time during which a soft washed roof will re-colonise and need soft washing again. But as a very rough approximation an "average" roof will stay clean for around 3-5 years.

The best way to give your customers the longest lasting clean on the first visit is to apply a strong treatment of Bio Cleanze at 20-25:1, ensuring the spray gets under the laps, between the tiles and in all other surrounding nooks, crevices, cracks and crannies.

The problem of overhanging trees

Moss will take longer to re-colonise than algae, although the presence of overhanging trees will encourage it.

Without overhanging trees a roof can remain clean of moss, lichen and algae for several years. This is especially true of relatively porous surfaces such as clay tiles when treated with Benz Bio Cleanze.

The presence of overhanging trees will mean that re-colonisation will inevitably happen more rapidly, sometimes as soon as 6-9 months in the case of green algae. This is due to the shielding from wind, shading from sun, and the accumulation of fallen leaves.

Quick tip: Just one leaf decomposing on a roof can give rise to the spread of algae, and can leave an unsightly green streak.

Fortunately this is not the norm and these green streaks will often die away in the spring and summer, or can be re-treated with a relatively weak solution of Bio Cleanze, say 40-50:1.

How to keep a roof clean, for longer

Scraping and then treating with Benz Bio Cleanze is our recommended way to treat most porous roof surfaces, and even many non-porous surfaces such as slate. Non-porous surfaces such as pvc coated steel cladding and plastic sheeting is usually best treated with Benz Lightning Cleanze at 5-10:1.

For a quick maintenance treatment it's possible to spray from the top down without the need to pay particular attention to the laps and joints as you would when giving a full treatment. 

Using our "Clean & Maintain" softwash systems means you will use less chemical and your time on site will be minimised.
Bio Cleanze will soak deeply into porous surfaces (even deeper than water can), providing residual protection against re-colonisation. How long that protection will last for is impossible to say in absolute terms because it depends on multiple factors, such as:

  • The local environment.
  • How much moss/lichen was on the roof.
  • How well the roof was scraped.
  • If the scrapings from the roof were thoroughly rinsed off (remember to block downpipes and clear the waste from gutters).
  • How deeply the moss (and lichen, etc) had been allowed to root into the surface.
  • The number of treatments given. Two applications on the first clean is often a good idea, to ensure the biocide soaks in deeply. If the colonisation is very severe another treatment after a month or two will sometimes be indicated.
  • The strength of Bio Cleanze as applied. We suggest diluting 20-30:1, depending on severity of the colonisation, when first cleaning. And a quick re-spray at 40-50:1 (winter/summer) every 12-36 months will keep most roofs permanently clean (this is cost-effective for customers because the time taken to give a quick re-spray is short and hence the cost is relatively low

    Using our "Clean & Maintain" approach to soft washing roofs your customers get to enjoy a permanently clean property, and you enjoy a regular stream of repeat business.

Click here to get more practical how-to tips for soft washing roofs

Quick tip: Enter a relevant "keyword" or short phrase into our in-site Search Engine to find answers to most of your softwashing questions (e.g. keyword for above link = "run-off")

We hope this information is helpful and sincerely wish you great success in your soft washing business,

Ben, Leo, Fiona, Stevie & Anthony

Order Benz softwash chemicals & equipment online or by phone:

GB (England, Scotland, Wales)

Phone: 0800 70 74 222 


Ireland and other countries

Phone: 00353 214 622 978


Lines open Monday - Friday, 9am – 5pm

Please note: The above numbers are for orders only (click here for tech support)

Click here to explore all Benz Softwash cleaning chemicals & equipment

Benz Softwash Bio Cleanze DDAC biocide & Benz Softwash Lightning Cleanze SH sodium hypochlorite biocide

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