Most homeowners notice roof moss in November, not July. The wet months are when it greens up and thickens enough to see from the driveway, which is also when the usual assumption kicks in: surely this has to wait for dry weather.
Mostly, no. Here’s what actually determines whether a roof gets treated now or in the spring, and what to expect from the result either way.
Why it looks worse in the wet months
Vancouver’s mild, wet winters are moss’s growing season rather than its off season. Cool temperatures and constant moisture suit it, so growth that was dormant and grey through a dry August is active and green by late autumn.
Where it shows up first is predictable. North-facing slopes stay shaded and hold moisture, and anything under cedar or fir gets a steady drop of needles and organic material that holds water against the surface. A sunnier slope on the same house can look fine while the north side is thick with it.
Treatment doesn’t need dry weather — but it does need safe weather
Soft washing isn’t like sealing or painting, where the surface has to be dry and the temperature has to hold. It’s a treatment applied at low pressure that works on the moss and algae, so damp conditions don’t stop it doing its job.
What does stop a visit is safety. We reschedule for heavy rain and high wind, which are safety calls rather than quality ones, and frost or ice on a sloped roof means nobody is walking on it that morning. Between those, there’s plenty of workable weather through a Vancouver winter — it just means being flexible about which day.
The method changes with the roofing material
This is the part worth getting right, because one approach doesn’t suit every roof:
- Asphalt shingle is always soft washed. Pressure strips the granules off the surface, which is the layer doing the protecting — it shortens the roof’s life rather than extending it.
- Cedar shake is treated at low pressure too. It’s a softer material and aggressive cleaning lifts and splits it.
- Tile can take a light, controlled pressure as part of the treatment, depending on its condition.
We look at the material and the growth before deciding on strength and dwell time. The approach for residential roof cleaning and moss removal is set by what’s actually on your roof, not by a single setting applied to everything. If you’re not sure what you have up there, our guide to roof washing walks through identifying it.
What the roof looks like afterwards
Worth setting expectations on, because this surprises people. Heavy, established growth is removed by hand where the roof allows, so the treatment reaches the surface underneath. The rest weathers off gradually over the following weeks rather than disappearing the day we leave.
A roof treated in November often looks noticeably better by January and better again by spring. If you’re expecting a bare, swept-clean roof the same afternoon, that’s the version that involves pressure, and pressure is what costs you shingle life.
Do the gutters in the same window
A moss treatment dislodges material that has to land somewhere, and somewhere is the troughs and valleys. We clear what we dislodge as part of the visit, but the sequence matters: treating the roof and then clearing the gutters makes sense, while doing it the other way round means handling the same debris twice.
Mid-to-late November is when the autumn gutter cleaning is due anyway, once the maples and oaks have finished dropping. Booking the two together is one visit, one access arrangement and one set of photos rather than two.
When waiting until spring is reasonable
Sometimes it genuinely is. If the growth is light, or the roof was treated within the last couple of years and this is surface algae rather than established moss, waiting for spring costs you very little.
If the moss is thick enough to hold water against the shingles or lift their edges, a season of active growing weather is the wrong thing to add to it. That’s the case for dealing with it now rather than in April.
Either way, roof treatments carry our moss-free guarantee, with the term confirmed in your written quote — if moss returns to the treated area within that period, we treat it again at no charge. Our work also carries a 100% satisfaction guarantee when you tell us within 48 hours of completion.
Send us your address and, if you can, a photo of the worst slope. We’ll tell you what the roof needs, what it doesn’t, and price it in writing before anything is booked. The residential services overview covers the rest of what we look after on a house exterior.