Biocides in roof cleaning
| Biocides in roof cleaning | |
| Purpose | Killing and inhibiting moss, lichen and algae |
|---|---|
| Governing regime | Regulation (EU) No 528/2012 as it applies in Great Britain |
| Also engaged | Control of Substances Hazardous to Health Regulations 2002 |
| Common misstatement | That an approved active substance means an approved product |
Most roof cleaning involves applying a chemical that kills biological growth or prevents its return, and any such product is a biocidal product regulated under Regulation (EU) No 528/2012 as it applies in Great Britain.[1] This article describes how that regime bears on the work. It does not name products or recommend concentrations, because the authorised terms are specific to each product and change.
Why the wording in marketing rarely means what it appears to[edit]
Three phrases recur in roof cleaning material and none of them establishes what a reader usually takes from it.
"Approved biocide" conflates the two decisions the Regulation makes separately: approval attaches to an active substance, authorisation to a product.[1] "Safe" is not a regulatory category; a product may be authorised for a use and still be a substance hazardous to health for the person applying it.[2] "Environmentally friendly" corresponds to nothing in the Regulation at all.
The question that carries information is whether the specific product is authorised for this use, and on what conditions.[1]
Application and the conditions of use[edit]
The Regulation covers use as well as supply, so the conditions attached to a product's authorisation govern how it may be applied.[1] Dilution rates, permitted surfaces, weather constraints and any restrictions on run-off are terms of lawful use rather than advice.
Roof application raises run-off directly, because whatever is applied to a roof reaches the gutters and then the ground or the drainage system. Where a product's authorisation restricts that, the restriction is part of the authorisation and not a matter for judgement on site.
The people applying it[edit]
The Control of Substances Hazardous to Health Regulations 2002 apply to the exposure of the people doing the work, separately from whether the product is authorised.[2] A product may be lawfully authorised and simultaneously a substance requiring assessment, control measures and, where those are insufficient, personal protective equipment.
The two regimes answer different questions. Authorisation asks whether the product may be placed on the market and used at all; COSHH asks what must be done to protect the person using it.
Soft washing and dwell time[edit]
The practice of applying a biocidal solution at low pressure and leaving the growth to die back over weeks is a consequence of how these products work rather than a technique in its own right: the chemical needs contact time. That is why a roof treated this way looks unchanged immediately afterwards, and why an expectation of instant transformation is a poor guide to whether the work was done properly.
No statute or published standard defines soft washing, and the description here is of established practice.
See also
- Biocidal Products Regulation
- Soft washing
- Control of Substances Hazardous to Health
- Biological growth on roofs
- Roof cleaning
References
- abcdRegulation (EU) No 528/2012 concerning the making available on the market and use of biocidal products. legislation.gov.uk. Retrieved 2026-09-05
- abThe Control of Substances Hazardous to Health Regulations 2002. legislation.gov.uk. Retrieved 2026-09-05