After Roof Moss Treatment: What Happens in Weeks 1 to 12

Day one: what you see straight away

Where moss has been removed by hand, the change is immediate. The cushions are gone and the tile shape is visible again. Gutters have been cleared of the debris that came off the roof.

Areas of algae, lichen and fine growth may look only slightly different. They have been treated but not yet rinsed away.

Weeks one and two

The biocide works into the remaining growth. Lichen may darken or look dry and flaky. Algae streaks may begin to lighten in patches. It is normal for the roof to look uneven during this stage.

Avoid trying to speed things up with a hose or brush from a ladder. The treatment does not need help, and climbing is the biggest risk in the whole process.

Weeks three to six

Each spell of rain rinses away more of the dead growth. Most owners notice a clear improvement in this period, particularly on algae streaks below chimneys and along the eaves.

Some small bits of material may wash into the gutters. That is expected and usually minor because the bulk was removed on the day.

Weeks six to twelve

By this stage the treated growth has generally faded or washed away. Lichen can be the slowest; small grey rosettes may take longer to loosen than algae or moss. Very dry weather slows the process because there is less rain to rinse the roof.

If an area still looks heavily green after a few months of normal rainfall, take a photo and send it to us so we can look at it.

Keeping an eye on gutters and downpipes

A quick look at the gutters from the ground after heavy rain is worthwhile. Water spilling over the edge or a downpipe that drips rather than flows can mean residue has collected. Our downpipe unblocking service deals with that if it happens.

What you should not see

You should not see slipped tiles, water in the loft or cracked tiles that were not there before. Low-pressure treatment and hand removal do not cause those problems, but if you notice anything unusual after any roof work, it is always worth reporting promptly.

How weather changes the timeline

A wet autumn rinses treated growth away quickly, so the roof can look clean within weeks. A long dry summer leaves dead growth sitting in place until the rain returns. Neither means the treatment has failed. Frost can also loosen dead moss, so a cold snap after treatment sometimes brings a sudden visible change.

Looking after the roof from now on

Once the treated growth has gone, keep an eye on the gutters each autumn and spring, and look at the shadiest slopes from the ground. Small green spots at tile edges are the first sign of moss returning, and an early light treatment is simpler than waiting for cushions to form again.

Patches that look different

Areas that were cleaned by hand will look different from areas that were only treated, at least for a while. Lichen-covered tiles may show pale outlines once the lichen has gone. These differences even out as the roof weathers.

When we might return

Occasionally a stubborn patch, often in the deepest shade, needs a second light treatment. If that happens, tell us and we will look at it.

Questions after your treatment?

If you would like advice on how your roof is coming along, or a quote for treatment in the first place, get in touch. Quotes are free across Hampshire, Surrey and Sussex.