Biocide roof treatment: the step that keeps a clean roof clean
Scraping moss off a roof removes what you can see. It does nothing about the microscopic spores and root threads left in the pores of the tile, and those are what turn a freshly cleaned roof green again within a couple of seasons. A biocide treatment is the part of the job aimed at that hidden layer.
We book biocide as its own service and as the finishing stage of a full roof clean. This page explains what the treatment does, when it is worth paying for, when it is not, and what you should expect to see on the roof in the weeks after we leave.
What the treatment is for
Moss, lichen and the black or green algae films found on Bedfordshire roofs all reproduce from spores that lodge in the surface texture of concrete and clay. A mechanical clean lifts the bulk growth but cannot reach into that texture without damaging it. A biocide is a liquid wash that soaks in and kills what is left behind, so regrowth has to start again from scratch rather than from a head start.
It is applied at low pressure through a soft wash system, the same gentle approach we use on render and uPVC. Nothing is blasted at the tiles, which matters because pressure is what strips the surface of a tile and makes it hold water.
Where it fits in a roof clean
- Hand clean first: thick moss cushions are lifted and scraped by hand, bagged and removed from site.
- Gutters cleared: the debris that falls during cleaning is taken out of the gutters rather than left to block them.
- Biocide applied: the whole roof is treated so the remaining spores and roots are dealt with.
- Weathering does the rest: over the following weeks the treated residue dies back and rain washes it away.
Treatment on its own
Not every roof needs scraping. Where the growth is a thin film of algae or scattered lichen rather than deep moss, a treatment by itself is often the proportionate answer. It costs less than a full clean and it avoids anyone walking the roof more than necessary.
We will tell you which category your roof falls into from photographs or a free visit. If the moss is thick enough that a treatment alone would leave dead clumps sitting on the tiles for months, we say so rather than sell the cheaper option and leave you disappointed.
What you will see afterwards
A treated roof does not change colour overnight. Lichen spots and algae staining fade gradually as the dead growth dries and weathers off, and the change is usually most obvious after a period of rain. That slow fade is normal and is a sign the product is working, not a sign it has failed.
Full roof cleans come with our written 24-month biocide guarantee, so if growth returns inside that period you are covered. Keeping gutters clear and cutting back overhanging branches helps the finish last beyond it.
Find out whether your roof needs a treatment
Send two or three photographs from the garden and we will tell you whether a treatment on its own or a full clean is the right call. Quotes are free.
Sky Scrapers Ltd · info@sky-scrapers.co.uk
Gardens, pets and neighbours
Because the wash goes on at low pressure, overspray is kept to a minimum and we work around planting, ponds and parked cars. We ask for pets to be kept inside while we are applying and until the roof surface has dried. Our separate guide on biocide safety covers plants and animals in more detail.
Our own photographs
Images from Sky Scrapers Ltd work showing the methods described on this page.
Where this applies locally
Towns where this comes up most often on our patch:
- Softwashing & Biocide Treatment in AmpthillBedfordshire · MK45
- Softwashing & Biocide Treatment in FlitwickBedfordshire · MK45
- Softwashing & Biocide Treatment in BedfordBedfordshire · MK40
- How biocide treatment works after a roof cleanGuide
- Biocide treatment and safety around your garden and petsSafety guide
- Hand cleaning or chemical treatment aloneBuyer guide
Questions we get asked
Is biocide the same as a roof coating?
No. A biocide kills growth and its spores and then weathers away. A coating is a paint-like layer. We explain our honest view on coatings in a separate guide, but a biocide treatment does not change the look or material of your tiles.
Can you treat my roof without cleaning it first?
Yes, where the growth is light. On roofs with thick moss we recommend a hand clean first, because treating heavy moss leaves dead clumps on the roof and in the gutters for a long time.
Does the guarantee cover a treatment-only visit?
The written 24-month biocide guarantee comes with full roof cleans. Ask us when you book and we will confirm in writing what applies to the work quoted.
Will the roof look clean straight away?
Scraped areas look clean on the day. Staining and lichen treated by the biocide fade over the following weeks as the dead growth weathers off.
Do you use a pressure washer to apply it?
No. It goes on through a low-pressure soft wash system. We never pressure wash roofs.
In short
Biocide deals with the spores and roots that scraping leaves behind. It is applied at low pressure, fades growth over weeks rather than hours, and full roof cleans carry a written 24-month guarantee.