Dirty shingles look streaky and flat, while damaged shingles curl, crack, or lift out of shape. A GAF-certified Master Elite Roofing Contractor that has been woman-owned and family-run since 2011, Coastal Windows & Exteriors has completed 7,000+ installations across Massachusetts, New Hampshire and Maine and provides professional roofing inspections and replacement. Knowing which one you’re looking at also affects how long your roof shingles last.
What New England Homeowners Should Look For
- Stains versus damage: Dark streaking is usually growth, not structural damage. Get a free estimate for a professional look.
- Flat and streaky: Algae on shingles reads as flat, dark discoloration. Real damage shows curling, cracking, or bare spots.
- Growth holds water: Moss on roof surfaces traps moisture against the shingle. Ask a pro how to remove moss from a roof.
- Stay off the roof: A ground level look has limits, so leave the climbing to professionals. Never walk your own roof.
- Warranty covers discoloration: GAF backs Timberline HDZ with a 25-year StainGuard Plus algae warranty. Its Time-Release technology helps limit staining.
- Age guides timing: GAF says roofs past 20 years deserve a professional opinion. Age, not dirt, usually drives when to replace roof.
- Cost of waiting: Emergency leak repair can cost nearly $1,800, up to twice a routine repair. A fall inspection catches issues early.
Knowing When to Call
Top Recommendation: Schedule a professional inspection before assuming stains mean damage or cleaning. Request your free roof assessment from Coastal Windows & Exteriors today.
Best for peace of mind: GAF-certified Master Elite contractors like Coastal handle inspections that protect your warranty.
Smart safeguard: Inspect your roof twice a year, in spring and fall, per GAF guidance.
Benefit: Asphalt roof replacement averages $35,701 in New England and returns 68% at resale.
Ready to stop guessing about those dark patches? Start with a professional roof inspection. Coastal Windows & Exteriors is a GAF-certified Master Elite Roofing Contractor, woman-owned and family-run since 2011. We earned the GAF Master Elite President’s Club Award for seven consecutive years, 2017 to 2023. Our team has completed 7,000+ installations. Book your inspection today.
Request a free roofing estimate from Coastal Windows & Exteriors.
Browse our complete roofing FAQ guide from Coastal Windows & Exteriors.
Explore the Coastal Windows & Exteriors Roofing Exterior Remodeling Home Improvement Help Center.
Still have questions about how do I tell the difference between a shingle that’s just dirty and one that’s actually damaged? See the areas we serve and talk to your local roofing contractor.
Last Updated: September 2026
Sources:
- GAF backs Timberline HDZ shingles with a 25-year StainGuard Plus Algae Protection Limited Warranty, aided by Time-Release Algae-Fighting Technology. GAF Timberline HDZ Time-Release Algae-Fighting Technology, the manufacturer’s announcement of the warranty and technology. (2022)
- Inspect your roof twice a year, and consult a professional about roofs over 20 years old or with recurring issues. GAF Residential Roofing FAQs, GAF guidance on inspection frequency and replacement timing. (2025)
- Emergency roof leak repair can cost nearly $1,800, up to twice the cost of a routine repair. This Old House Emergency Roof Leak Repair, consumer guidance on emergency roofing costs. (2025)
- Replacing an asphalt roof in New England averages $35,701. Remodeling Magazine (JLC Online) 2025 Cost vs. Value Report, New England, regional remodeling cost data. (2025)
- Asphalt roofing returns about 68% of its cost at resale. Remodeling Magazine (JLC Online) 2025 Cost vs. Value Report, national and regional remodeling ROI data. (2025)
