Start with age and spread together. A single failed detail (a boot, a flashing run, a valley) on a roof with flexible, granule covered shingles is a repair at almost any age. Failures appearing in different places in the same year, on shingles that crack when lifted, are the roof announcing its end as a system.
The Port Arthur arithmetic adds exposure to the usual age and spread. A roof at 16 years, sheltered in the interior streets, may honestly repair forward; the same roof open to Sabine Lake has spent its life faster, in fastener corrosion and wind cycles no inland calendar counts. Ask the scope to state the home's exposure class and the deck's condition, because on this coast those two facts, not the shingle birthday, make the repair or replace call.
Then the arithmetic: list the repairs the roof plausibly needs in the next two years, not just today's. If that list reaches a third to a half of a replacement price, replacement usually wins, and it resets every component at once: decking checked, underlayment, flashing, ventilation, and covering on one clock.
Where repair clearly wins: a sound roof under about 15 years with one cause. Where replacement clearly wins: brittle mats across slopes, multiple damaged sections, or documented storm damage on an older roof. Everything between deserves both prices in writing before anyone signs.
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