You hear over and over again that you should keep your roof clean; free of moss and debris. Here in Portland, OR, you see roofs covered in pine needles and moss all over the place – so why is keeping them clean so vital and necessary? Here is more information on what debris can do to your roof:
Branches/Leaves/Needles
These debris carry a few problems: 
First is that bugs likes dark, moist places like debris piles for their homes. One such bug is the boring beetle, which will go beyond the debris pile and into your roof.
Another problem is the debris can block water from running down the roof in the path it’s supposed to run. This causes pooling and can lead to the water getting in under the shingles and ultimately leaking into your home.
Finally, large branches or piles of debris can scrape up your roof – leading to premature wear. Getting them off of your roof as soon as possible can stop wind and rain from yanking the debris – and a shingle or two – off for you.
Moss
Moss is a plant – so it actually puts down tiny roots. This means that by growing on your roof, the moss is actually damaging your shingles. The moss will wear your roof down little by little until the roof covering becomes prematurely weak.
There are a few ways to avoid issues with roof debris. One is to get a metal roof installed. These roofs are much tougher than your average shingle roof and they can be treated to stay moss-free. Another is to get your roof cleaned and get any leak-prevention maintenance done. Finally, you can get your roofing material sealed so that it takes a higher degree of battering to harm it.
If you are concerned about roof damage or leaks, your local Portland roofer can give you a free estimate.