Lichen, Moss and Shade: Looking After a South-Facing Roof

South-facing slopes in Wellington get little direct sun for much of the year. Add damp air off the harbour and a few trees, and you have ideal conditions for moss and lichen. Many homeowners notice a roof that looks fine on the north side and green or grey on the south.

Why it matters

Moss holds water against the roof long after rain has stopped. On concrete tiles and Decramastic chip that constant damp speeds up wear on the surface. Moss also sheds into gutters and valleys, which is one of the reasons hillside gutters block so often, as covered in our hill-site gutter guide. Lichen grips tightly and can etch coatings, leaving patches that weather faster than the rest of the roof.

What makes a roof more prone

Rough surfaces give spores somewhere to grip, so tile and chip roofs tend to grow more than smooth long-run steel. Overhanging trees add shade and leaf litter. Areas below a valley or under a satellite dish that stay wet for longer often show growth first.

Treatment, not scraping

Scraping or water blasting can damage tile surfaces and strip coatings. A better approach is usually a biocide wash that kills growth and lets it break down over the following months, sometimes with a gentle soft wash first. Roof Repair Wellington describes its approach as soft wash and treat. If your roof has plenty of growth, a moss and lichen treatment before winter gives the product time to work while conditions are still mild.

Stopping it coming back

Trim branches that shade the roof, keep gutters clear and plan a regular treatment on shaded slopes. Look at the roof after each winter and act while growth is light. Our pre-winter roof checklist includes moss in its list of things to check, and it is a good time to look for cracked tiles or worn coatings that the growth may have been covering.

For safety, treatments are best done by people with the right access gear. Wet moss on a roof is slippery.