A soft green carpet of moss on a roof gives a home a fairy-tale look, but this story won't have a happy ending. Moss is indicative of an issue with the roof and it aggravates the damage. The following can help you better understand the dangers of the moss on your roof.
Moss is a nonvascular plant that doesn't produce roots. Instead, it has small rhizoids that do little more than keep it anchored. The anchoring substrate on your roof is thin, which is why moss may blow off easily or peel off in sheets during heavy rain. The good news is that this lack of roots means that the moss isn't actually piercing and putting holes in your shingles.
Moist conditions and cool to mildly warm temperatures lead to the most moss growth as it will dry up and go dormant when it is dry or when summer heat or freezing winter temperatures prevent it from accessing water. This is why moss is more common in northern latitudes, particularly on shaded north-facing roofs or those under heavy tree cover.
The damages caused by moss are typically indirect. As moss reproduces and releases spores, some of these spores may begin to grow on the edge of a shingle. As the moss clump gets larger, it pushes its way beneath the shingle and lifts it up. Now water can seep beneath the lifted shingle and seep into your attic.
This pushing up of a shingle can also loosen the shingle or cause it to break. Further, all the moisture trapped in the moss can speed degradation of the shingle surfaces. Most alarming is the weight wet moss can add to a roof. In extreme cases, this weight could exceed how much the roof can hold.
A roof cleaning is the first task when you want to reclaim your roof from the moss. A moss killer, which often contains bleach, is sprayed onto the roof and the moss is rinsed away. Your roofer will then inspect the roof for damages so that any broken or decaying shingles can be replaced before they fail completely.
You must also take steps to prevent the moss from regrowing. Your roofer can install zinc strips near the peak of your roof. The zinc will leach down over the rest of the roof, killing the moss. Your roofer may also advise that you trim back trees to increase airflow and light so the roof won't be as prone to moss growth.
For more help, contact a residential roof repair service in your area.