You are buying five things, not shingles
Roofing bids are usually presented as a material and a price, which hides where the quality differences actually live. A replacement is an assembly, and each layer has a job:
- The deck. The structural sheathing everything else fastens to. Its condition cannot be assessed until the old covering is off, and soft or delaminated sheathing will not hold fasteners at their rated withdrawal resistance.
- The underlayment. The secondary water barrier. Felt, synthetic and self-adhering ice-and-water membrane are not interchangeable, and where each is required varies by code and climate.
- The flashing. Every penetration, valley, wall transition and edge. Reusing old flashing to save money on a new roof is the most common corner cut in the trade, and the most expensive one.
- The covering. The visible material that sheds the weather and takes the UV load.
- The ventilation. Balanced intake at the soffit and exhaust at the ridge. Get this wrong and the assembly cooks itself from underneath, in every climate, in both summer and winter.
When two bids differ by thousands, the difference is almost never the shingle. It is whether the flashing is new, whether the underlayment specification matches the code requirement, whether deck repair is priced honestly, and whether ventilation is being corrected or ignored.
Tear-off versus overlay
An overlay — installing new shingles over the existing layer — is cheaper on the day and worse in nearly every other respect. Most codes permit at most two total layers, so an overlay forecloses the option next time. It hides the decking, which means any rot present stays there and keeps progressing. It adds substantial dead load. It transmits the irregularities of the old surface through the new one. And it typically reduces or voids the manufacturer's warranty.
We tear off. The exception is narrow: a single-layer roof in good plane with no known deck issues, where budget genuinely forecloses the correct approach and the owner understands the trade. Even then we say plainly what is being deferred rather than presenting it as equivalent.
Material comparison
| Material | Typical service life | Strengths | Trade-offs |
|---|---|---|---|
| Architectural asphalt | 22–30 years | Best cost-to-life ratio available, wide colour range, repairable, installable on almost any steep-slope geometry. | Degrades faster in high heat and intense UV; performance is highly sensitive to attic ventilation. |
| Three-tab asphalt | 15–20 years | Lowest initial cost. | Lower wind ratings, shorter life, and a small saving per square against architectural for a meaningfully worse product. Rarely the right economics. |
| Standing-seam metal | 40–70 years | Concealed fasteners, excellent wind and fire performance, sheds snow well, reflective options reduce cooling load. | High initial cost, requires an experienced installer, and panel expansion must be accommodated in the detailing. |
| Exposed-fastener metal | 25–40 years | Considerably cheaper than standing seam; common on agricultural and outbuilding applications. | Thousands of exposed gaskets that age out; expect a re-fastening cycle partway through the life. |
| Concrete or clay tile | 50+ years (underlayment 20–30) | Very long covering life, excellent in heat, non-combustible. | Heavy — framing must be verified. The underlayment fails long before the tile, so a mid-life lift-and-relay is expected work, not a defect. |
| Synthetic slate and shake | 30–50 years | The appearance of slate or shake at a fraction of the weight and cost, with better impact ratings. | Product quality varies widely between manufacturers; the warranty is only as good as the company behind it. |
| Wood shake | 20–30 years | Appearance, and sometimes required by historic districts or covenants. | Maintenance-intensive, fire restrictions in many jurisdictions, and insurance implications worth checking first. |
| Single-ply membrane (low-slope) | 20–30 years | The standard for commercial and low-slope residential. TPO and PVC are heat-welded; EPDM is adhered or seam-taped. | Performance is governed by seam quality, terminations and drainage. Ponding water is the enemy. |
What happens during the work
Before
Permit pulled where required. Materials delivered and staged to spread load rather than concentrate it. Property protection: tarps over landscaping, plywood against siding at drop zones, vehicles moved clear. Owners are told which day is the loud one, because tear-off is genuinely loud and it transmits through the structure.
During
- Tear-off down to the deck, with debris controlled rather than allowed to accumulate against the building.
- Deck inspection with the sheathing exposed. Soft, delaminated or rotten sheets are marked and replaced. This is where the per-sheet rate agreed in the proposal applies, and where we photograph everything replaced.
- Drip edge at eaves and rakes, then ice-and-water membrane where code or climate requires it — eaves, valleys, and around penetrations.
- Underlayment across the field, lapped to specification.
- New flashing at every penetration and transition. New pipe boots, new step flashing, new valley metal. Old flashing is not reused.
- Covering installed to the manufacturer's published fastener pattern and exposure, which is what the material warranty is conditioned on.
- Ridge ventilation cut and installed, with intake verified as adequate rather than assumed.
After
Magnetic sweep of the perimeter for fasteners, repeated. Gutters cleared of granules and debris. Final walk-through with photographs of the completed details. Manufacturer warranty registered where the system qualifies for it, which frequently requires that specific components were used together — a reason not to substitute accessories to save a small amount.
Ventilation: the part nobody quotes
Attic ventilation is the most consistently neglected element of a replacement, and it directly determines how long the new roof lasts. The general rule is one square foot of net free ventilation area per 150 square feet of attic floor, split roughly evenly between intake at the soffits and exhaust at or near the ridge.
Two failure modes recur. Exhaust without intake — ridge vent installed above blocked or absent soffit vents — which produces no airflow at all and can pull conditioned air out of the house. And mixed exhaust types on one attic space, such as a ridge vent combined with powered or gable vents, which short-circuits: the ridge vent draws from the nearest opening instead of from the soffits, leaving most of the attic unventilated.
In summer an unventilated attic superheats and bakes the shingles from below. In winter it accumulates moisture that condenses on the sheathing, and warms the roof deck enough to drive the melt-refreeze cycle that causes ice dams. Both shorten the life of the covering you just bought.
Ask every bidder three questions. Is the deck repair rate stated per sheet in the contract, or is deck work an open change order? Is all flashing new, or is existing flashing being reused? What is the ventilation calculation for this attic, and what is being changed to meet it? The answers separate bids far more reliably than the shingle brand does.
If your roof is not actually at the end of its life, none of this is urgent — a targeted roof repair is the better spend, and Sunny San Luis Roofing will tell you so after inspecting rather than after tear-off.