Neighbors are getting new roofs. Homes built around the same time period can be experiencing the same types of weather conditions can mean that your roof is nearing its useful life.
Dark streaks. Airborne algae cause dark streaks on roof decks. While this may not necessarily harm the roof shingles, it may not look good.
Moss can grow on roof surfaces that don’t get much sunlight, especially in cool, moist climates. Moss growth can be more than a cosmetic issue. Moss holds moisture against the roof surface and over time in freezing climates can cause damage to the granules on the top of the shingles. Moss can be brushed off but it won’t prevent it from growing again; take care not to damage the shingle surface. You may need to contact a professional roofing contractor.