That's almost always algae growth, driven by Florida's humidity, and it's much more common on standard shingle lines than on algae-resistant (AR) products, which use copper-infused granules specifically to resist it.

Generally yes — architectural shingles are thicker, have a longer realistic lifespan, and perform better in wind than 3-tab, which is increasingly hard to find as a primary product in high-wind regions anyway.

HVHZ installation requires a 6-nail fastening pattern per shingle, not the 4-nail pattern common in lower-wind parts of the country — a detail worth confirming with any contractor before work begins, since it's easy to shortcut and hard to verify after the fact.

No — overlay is not permitted in HVHZ jurisdictions. Full tear-off to decking is required, which is also the right time to correct any underlayment or ventilation issues the old roof had.

Shingles rated 25-30 years nationally realistically perform closer to 15-25 years in South Florida's UV and heat — worth planning around rather than the manufacturer's headline number alone.

Balanced ventilation — enough ridge exhaust matched to enough soffit intake — measurably affects both shingle temperature and lifespan, plus your cooling costs; it's worth evaluating at the same time as a shingle replacement.

Yes, as long as the specific shingle product carries a current Miami-Dade Notice of Acceptance and is installed to the required high-wind fastening pattern.

Architectural shingle is generally the most affordable full-replacement option and the fastest to install, though it carries the shortest realistic lifespan of the common systems used in South Florida.