Roof cleaning and moss removal in Northern Germany, Sweden and Denmark

Roof cleaning removes moss, algae, lichen, leaf debris and stubborn dirt from clay tiles, concrete tiles and fibre cement sheets. It is not only about appearance: a clean roof dries faster after rain, water runs freely into the gutter, and the tile surface is no longer kept permanently damp.

In the Baltic region, growth takes hold easily. Sea air, frequent rain and high humidity keep roof surfaces wet for long periods, and north-facing slopes or roofs shaded by trees often turn green within a few years. That applies to houses in Rostock just as much as to homes in southern Sweden or on the Danish islands.

Roof cleaning is also the first step of every roof coating and every sealing treatment. New protective layers only bond to a surface that is free of organic growth and loose particles.

A green or dark film on the roof is more than a blemish. Moss acts like a sponge, holding rainwater and releasing it slowly. In winter that water can freeze in the pores of the tile, and repeated freeze–thaw cycles gradually make the surface flake. Look out for these signs:

Once moss cushions fill the overlaps between tiles, wind can drive rain underneath the roof covering. At that point cleaning should not wait. A few photos taken from the garden or a window are usually enough for us to give you a first opinion.

Before any cleaning we look at the roof: which material is it, how old is it, are there broken or slipped tiles, and how heavy is the growth? These answers decide the pressure we use. An engobed clay tile – one with a thin, fired-on clay finish that gives colour and a smoother surface – needs different treatment from an older concrete tile whose factory colour has already weathered away.

We remove thick moss by hand first. The surfaces are then cleaned with water pressure adjusted to material and condition, and on sensitive materials we work with low pressure – better one extra pass than a damaged surface. Joints around chimneys, dormers and roof windows and the ridge area are treated manually, because growth clings hardest there.

Loosened material partly ends up in gutters and downpipes, so clearing them is part of the finish. We then check the result and note anything unusual, such as cracked tiles, so you know whether further work is needed. You do not have to be at home while we work.

The best time for roof cleaning is between spring and autumn, when the weather is dry and frost-free. Removing moss before winter is sensible so that it cannot hold water that freezes. We do not work on the roof during storms, heavy rain or icy conditions.

Common pitched-roof coverings can be cleaned: clay tiles, concrete tiles and asbestos-free fibre cement. How much pressure a material tolerates is decided on the individual roof, not by a fixed rule – two roofs of the same material can differ a lot depending on age and exposure.

There are clear limits. Older fibre cement sheets may contain asbestos. Asbestos-containing sheets should only be handled by licensed specialist firms, and in Germany uncoated asbestos cement roofs may not be cleaned or coated at all. Crumbling tiles that break when stepped on, or a roof with a damaged underlay, cannot be saved by cleaning either.

Flat roofs with bitumen or membrane coverings and thatched roofs are not suited to cleaning with water pressure. If you are unsure what your roof is made of, send us close-up photos and we will help you find out.

Cleaning alone is enough when the tiles are intact, the surface is still closed and the problem is mainly growth. Afterwards the roof looks cared for and dries better. Expect algae and moss to return on an untreated surface over time, though – faster on rough concrete tiles than on smooth clay.

To slow regrowth on a roof that is still in good condition, the cleaned tiles can be sealed with an impregnation. It penetrates the pores without forming a film, so water runs off and the appearance barely changes. Some tile manufacturers advise against later treatments, so we check suitability first.

If the surface is already porous, faded or sandy to the touch – typical of older concrete tiles – a roof coating is the better option. It closes the surface and gives the roof a new colour. And if many tiles are broken or the roof leaks, the right first call is a roofer; we will tell you so.