When should you remove moss from your roof?
By the Toiture Wash team · Updated on 20 October 2026 · 4 min read
Short answer. The right time to remove moss from a roof is a dry period without frost: in Belgium, spring and early autumn are the best times. But the condition of the roof decides, not the calendar: when the moss forms cushions at the overlaps or the gutters overflow, it is time.
Good conditions, rather than a good season
Two conditions matter more than the month:
- No frost. A roof wetted by the cleaning must not freeze overnight, and a frosty roof is dangerous for whoever works on it.
- Dry weather. Cleaning works better on moss that is not soaked; when the moss removal ends with a water repellent, it needs a dry roof and no rain after application.
That is why mild periods, in spring and early autumn, are the most suitable.
What our requests show
We receive requests all year round, but not at the same pace. Two seasons stand out:
- The roof, from February to April. The moss has thrived during the damp winter and shows up with the first sunshine: that is when we receive the most requests. For a job in spring, ask for your quote in winter: it is valid for three months.
- The gutters, in October. The leaves fall, and the gutters overflow at the first autumn rains. The best time to clean them is just after the leaves have fallen.
November and December are the months when we receive the fewest requests.
The telltale signs
- Cushions of moss at the tile overlaps, at the ridge or around the chimney.
- Pale or dark patches that spread: often lichens, which cling on more firmly than moss and take longer to remove.
- Gutters that overflow in rain, or moss at the foot of the downpipes.
- One side that turns green more than the other: the north side and the slopes under trees dry more slowly.
- Tiles that look lifted or misaligned when seen from the garden: moss can lodge underneath. Have the roof covering checked in that case.
What moss really does to a roof: Moss on the roof: what are the risks?
How often?
There is no universal rule, and the figures you read online (every 5 to 10 years, every 7 or 8 years) are not, to our knowledge, based on any published measurement. The interval depends on four things:
- Exposure: a north face, a roof under trees or near a wood turn green again faster.
- The material: a porous tile holds more water than a natural slate.
- The treatment: after the moss removal, the roof receives either a water repellent, which waterproofs it, or an algicide product, which slows down moss regrowth. At Toiture Wash, this treatment is included in every moss removal.
- The surroundings: damp, wind, tall hedges.
The simplest approach: look at your roof at the end of every winter, from the street and from the garden, and have the gutters cleaned every year.
The Belgian climate, in brief
In Uccle, the reference station of the Royal Meteorological Institute (IRM), an average of 837.3 mm of rain falls per year, spread over 189.8 days of rain, and there are 39.4 days of frost (1991 to 2020 normals). No month is short of rainy days: from 13.1 in April, the driest month, to 19.4 in December.
| Month | Rain (mm) | Rain days |
|---|---|---|
| January | 75.5 | 18.9 |
| February | 65.1 | 16.9 |
| March | 59.3 | 15.7 |
| April | 46.7 | 13.1 |
| May | 59.7 | 14.7 |
| June | 70.8 | 14.1 |
| July | 76.9 | 14.3 |
| August | 86.5 | 14.3 |
| September | 65.3 | 14.1 |
| October | 67.8 | 16.1 |
| November | 76.2 | 18.3 |
| December | 87.4 | 19.4 |
IRM normals at Uccle, 1991 to 2020; a rain day is a day with at least 0.1 mm. This damp climate all year round explains why moss grows everywhere in Belgium, and not only on north faces. It also explains why April and May, which are drier, suit a moss removal followed by a treatment.
Frequently asked questions
Should you remove moss before selling your house?
A clean roof and clean gutters make a better impression at viewings and show regular upkeep. It is also a chance to spot a tile to replace before the survey.
Should you remove moss every year?
No, the roof does not need it every year; the gutters, however, benefit from being cleaned every year, especially near trees.
Sources
- Quote requests received by toiturewash.be in 2024 and 2025 (monthly averages).
- IRM, Annual climate summary 2024 (in French); Brussels Environment (Bruxelles Environnement), Past evolution of the climate in the Brussels Region (in French), table 2.3 (1991 to 2020 normals at Uccle).