Moss and Lichen — Not Just Appearance
To many homeowners, moss on the roof is an aesthetic problem — the roof looks old and dirty. In reality, moss and lichen cause serious structural damage that slowly and irreversibly deteriorates the roof covering.
How moss damages tiles: The moss layer acts like a sponge, absorbing and holding moisture against the tile surface. Moisture penetrates the micro-pores of tiles. In winter it freezes and expands — tiles crack and split from the inside. This is called the freeze-thaw effect and it is the primary mechanism of tile deterioration in Latvia. A moss-covered tile roof deteriorates 15–20 years faster than a clean one.
How lichen damages surfaces: Lichen is a symbiosis of fungus and algae — it adheres very tightly to mineral surfaces. Lichen excretes organic acids that slowly etch the tile glaze, stone surfaces and even concrete. On metal roofs lichen retains moisture against the metal, accelerating corrosion. On slate roofs lichen acids slowly work through cracks.
Fact: Research shows that a roof with a thick moss covering can retain moisture for 24–48 hours after rain, while a clean roof dries within 2–4 hours. This chronic moisture accumulation is directly responsible for accelerated material deterioration.
How the Problem Looks — Recognise the Signs
Green Moss Coverage
Visible green moss growth on tiles or slate — especially on the north side and in shaded areas. Starts at the edges, then spreads toward the centre.
Grey or Black Lichen
Flat, greyish-green or greyish-white structures firmly adhered to tile or metal surfaces. Often visible on older roofs.
Organic Deposits
Brown or dark streaks from leaf matter, bird droppings and organic material accumulation — often forms near gutters and valleys.
Blocked Gutters
Leaves, moss fragments and other organic material block gutters and their outlets — water does not drain, accumulates at the eaves.
Reduced Property Value
A moss-covered roof visually reduces the value of the property and gives the impression of a neglected house — significant if you plan to sell.
Moisture Retention
After rain the roof stays damp for a long time — the moss layer delays drying and maintains constant moisture in the tile pores.
Pressure Washing — What Pressure is Needed
One of the most common mistakes in DIY roof washing — too high a pressure. A domestic pressure washer used for car washing or terrace cleaning can seriously damage the roof if used incorrectly.
Tile Roof
Clay and concrete tiles need pressure of 80–120 bar from at least 30–40 cm distance with a wide-angle nozzle (40°). A direct high-pressure jet can strip the glaze and create micro-fractures. For older, worn tiles — even lower pressure (60–80 bar). A professional specialist assesses each roof's specific condition.
Metal Roof
Profiled steel and aluminium sheets tolerate higher pressure (100–150 bar), but treatment must go across the corrugation direction, not along the seams — pressure must not be forced into the seam joints. On corroded metal roofs — lower pressure, as weakened metal is more brittle.
Slate Roof
Slate is a fragile material — pressure washing should use only lower pressure (40–60 bar) with a wide fan nozzle and from a distance. Direct high pressure can crack slate. Often a low-pressure washing system with biocide solution is better for slate cleaning.
Tip: Do not pressure-wash your roof yourself without experience — wrong pressure can damage seams and flashings. Professional cleaning uses the right pressure for each roofing material.
Roof Cleaning in Riga — Indicative Prices
The cost depends on the roof area, contamination level and service type chosen:
| Type of work | Price from |
|---|---|
| Basic washing | €3/m² |
| Washing with chemical treatment | €5/m² |
| Washing + moss removal | €6/m² |
| Washing + impregnation | €8/m² |
| Inspection and estimate | FREE |
Prices are indicative. An exact estimate is prepared after a free on-site inspection. The price is fixed — no additional invoice after work begins.
What Clients Say About Roof Cleaning
"Our tile roof was completely green with moss and algae — it looked terrible. They cleaned the whole surface with chemical treatment and applied impregnation. Now it looks almost new. Neighbours actually asked who did the work. Very pleased with the result."
Frequently Asked Questions about Roof Cleaning
How often should a roof be cleaned?
It depends on the environment and roof type. In shaded or damp locations moss grows faster — cleaning every 3–5 years may be needed. In open, sunny locations every 5–8 years is typical. After cleaning with impregnation, the interval can be extended significantly.
Will moss grow back after cleaning?
Without treatment, yes — moss spores are always present in the air. With a biocide chemical wash and subsequent impregnation, regrowth is significantly slowed — typically 5–7 years. We recommend combining cleaning with impregnation for the best long-term result.
Is high-pressure washing safe for all roof types?
No. Each material requires different pressure settings. Slate needs low pressure (40–60 bar), tile needs 80–120 bar with a wide nozzle, metal can tolerate slightly more but must be done across the corrugation, not along seams. Our technicians adjust the equipment for each specific roof.
Does cleaning damage the roof coating?
Correct professional cleaning does not damage the roof — in fact it extends its life by removing the moisture-retaining moss and lichens that accelerate material degradation. Incorrect pressure or technique, however, can cause damage — which is why DIY pressure washing often does more harm than good.
What time of year is best for roof cleaning?
Spring and early autumn are ideal — temperatures are moderate and the roof is not frozen. Summer is also suitable. Winter cleaning is possible in mild weather but frost makes some chemical treatments less effective. We can advise on the best timing for your specific roof.