Understanding how a roof is actually installed helps you tell a quality job from a corner-cutting one before it's too late to matter.
The decking under your shingles
The plywood or OSB decking is the foundation the entire roof relies on, and soft or rotted sections must be replaced during a tear-off. Skipping bad decking to save money guarantees the new roof will fail early over those spots.
Tear-off versus roofing over
Roofing over an existing layer is cheaper and faster but hides decking problems and voids many warranties. A full tear-off costs more but lets the roofer inspect and repair the wood beneath, which is the only way to guarantee a sound, long-lasting roof.
Hidden costs that show up mid-project
Rotted decking, inadequate old ventilation, and code-required upgrades can add cost once the old roof is off. A good roofer explains how these are handled and priced before work starts, so there are no surprises.
Signs your decking is failing
Spongy spots underfoot, sagging between rafters, and visible daylight or water stains in the attic all point to decking that needs replacement. Sound decking is non-negotiable for a roof that will last.
Underlayment and ice-and-water shield
Underlayment is the secondary barrier beneath the shingles, and synthetic underlayment outperforms old felt. In valleys and along eaves, an ice-and-water membrane seals against wind-driven rain and, in cold climates, ice dams.
Frequently Asked Questions
Can I just roof over my old shingles?
You can, but it hides decking problems and voids many warranties, so a full tear-off is almost always the better long-term choice. Tearing off lets the roofer find and fix damage underneath.
How much does a new roof cost?
Cost depends on the roof's size, slope, material, and complexity, plus whether the old roof needs tear-off and any decking repairs. The most reliable number comes from a free, itemized inspection and estimate rather than a phone quote.
What are the signs I need a new roof?
Curling or missing shingles, granules in the gutters, dark worn patches, a sagging roofline, and daylight or stains in the attic are the classic warning signs. Several of these together usually mean replacement.
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