Take a look at the photo below, this is a 38-year-old roof with bucket-loads of moss on it:

There is some very light pitting of the surface, but no more so than you would expect from 38 years of water, snow, ice, wind and UV damage.

It’s very likely that the concrete tiles on that roof will outlive the owners.

In extreme cases, moss can damage the tiles, but on most roofs the damage is superficial.

Moss can cause indirect damage to the roof and other parts of the home, and these should be of concern:

Reduced Drainage

If excess moss prevents water from draining off the roof, it may backup the roof and onto the underfelt, eventually making its way into the property:

Blocked Rainwater System

Moss decays into a thick muddy sludge, caking and blocking gutters, rainwater pipes, underground pipes and soakaways, this can cost thousands to dig up and replace.

The gutter shown below is completely blocked:

If the gutters overflow, damp may appear on the wall below and any timber fascias, soffits or window frames can rot.

Clay Tiles

Clay tiles are more fragile than the popular concrete tiles and are susceptible to damage from freezing and thawing in the winter.

If the roof has excess moss, the clay tiles won’t have the chance to dry out and as the roof is wetter for longer, there’s more damage from freezing/thawing.

Mortar

Sand and cement, and on older roofs; sand and hydraulic lime, can fail early if allowed to stay wet for longer during the winter months, again due to freezing/thawing. This can lead to ridge, verge, and hip tiles coming loose.

Summary

In most cases, normal levels of moss growth do little direct damage to concrete tiles.

In rare corner cases, excess moss can damage and shorten the life of the tiles.

Excess moss should be removed from clay tiles.

Indirect damage is common on many roofs and there are legitimate reasons to have the moss removed – blocked gutters being the one we see the most.

Many customers also choose to have the moss removed for aesthetic reasons or because they are tired of cleaning up bits of moss from patios, driveways lawns etc.

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