Why does moss matter to the covering?
Because moss holds water against the shingles and under their tabs, and a shingle that stays wet for long periods wears faster and lifts more easily.
Moss does not eat the shingle, but it changes the conditions the shingle lives in. A mat holds moisture against the surface through long wet spells, and the water works under the tabs where the sealant strip has weakened. Over time the tab lifts and the next wind can tear it away, and the mat keeps the water on the exposed edge.
A roofer who cleans a mossy roof checks what the moss has been covering. A lifted tab or a cracked shingle under a thick patch is common, and it is the reason the first step is always the covering, not the moss.
- Moss holds water against the shingle surface
- Water works under lifted tabs and softens the sealant
- A lifted tab under moss is a repair the cleaning reveals
Why is cleaning done before a treatment?
Because a treatment laid over a thick mat does little, and it runs off into the gutters and the soil before it has worked.
The FACTS sheet records that the roof must be cleaned before any moss treatment. The reason is practical. A treatment needs to reach the moss itself, and a thick mat stops it. The result is a patch that looks treated and is not, and the runoff goes into the drains.
The roofer clears the roof first, then decides whether a treatment is worth applying. Where it is applied, it is named on the record, so the homeowner knows what went onto the roof and where it went.
- Clean first, so the treatment reaches the moss
- Name the product on the record
- Plan the runoff before the treatment goes on
Why are pressure washers avoided?
Because high pressure strips the granules, lifts the tabs and can drive water under the covering, and it does more damage than the moss.
A pressure washer is quick, and it is the most common way homeowners damage their own roof. The jet strips the granules from the shingle surface, lifts tabs from the sealant and drives water under the covering at the joints. The moss goes, and the covering is shorter-lived afterwards.
Hand clearing and soft tools take longer and leave the covering in better condition. A roofer who offers a pressure wash on a shingle roof should be asked to explain why.
- Granules are stripped by high pressure
- Tabs are lifted and water is driven under
- Hand clearing keeps the covering longer
What should the record show after cleaning?
The state of the covering before and after, the damage found under the moss, the cleaning method, the treatment and its product, and the date of the next check.
A cleaning record makes the next visit easier. It should show the roof before and after, name each lifted tab or cracked shingle found under the moss, state the method and any product used, and set a date for the next check.
Keep the record with the roof file, so a later roofer or an insurer can see what was done and when.
- Before and after photographs
- Damage found under the moss, by position
- The method, the product and the next check date
