Reroofing means putting a new roof surface on an existing structure, and it happens one of two ways: an overlay (new shingles laid over the old layer) or a tear-off (everything stripped to the deck before new material goes on). An overlay runs about 25 to 40 percent cheaper up front but lasts roughly 16 years, while a tear-off lasts 20 to 30 years and is the only method that lets a crew inspect the deck. Choosing between them, then choosing a re roofing company that will do it right, is the whole job.
This guide separates the two methods, prices them, walks the code rule that decides whether an overlay is even legal on your house, and gives you a vetting checklist for the reroofing company before you sign.
What is reroofing?
Reroofing is the process of installing a new roof covering on a building that already has one. It splits into two methods: a roof overlay (also called a roof-over or layover), where new asphalt shingles are nailed over the existing single layer, and a full tear-off, where the old covering, underlayment, and flashing come off down to the wood deck before a new system goes on. The word “reroofing” is used by roofers and by the building code for both, but the two methods behave very differently over time.
An overlay is faster and cheaper because no old material is removed or hauled away. A tear-off costs more and takes longer, but it is the only method that exposes the deck, underlayment, and flashing so a crew can find and replace rot, and it resets the roof to full expected lifespan. A tear-off is a full roof replacement; an overlay is a partial one. Our guide to the average cost to tear off and replace a roof prices the tear-off as its own line item.
Roof over vs tear off: how the two methods compare
A roof-over installs new shingles on top of one existing layer, saving on labor and disposal but adding weight, trapping heat, and hiding the deck. A tear-off strips to the deck, adds disposal and often deck repair to the bill, and delivers the longer-lasting, code-clean result. The table below lays out the trade-offs that drive most reroofing decisions.
| Factor | Overlay (roof-over) | Tear-off |
|---|---|---|
| Typical cost vs the other | About 25 to 40 percent less up front | Baseline (adds disposal, ~$1 to $3 per sq ft) |
| Expected lifespan | Around 16 years | 20 to 30 years for asphalt |
| Deck inspection | None, deck stays hidden | Full deck, flashing, underlayment inspected |
| Timeline | Roughly 25 percent faster | Longer, includes tear-off and haul-away |
| Weight on structure | Adds a full second layer | Net neutral, old layer removed |
| Leak tracing later | Harder, water travels between layers | Straightforward, single layer |
| Manufacturer warranty | May be reduced or voided | Full warranty eligibility |
| Code limit | Only if one layer exists now | Always allowed |
The short version: an overlay buys time and saves cash today, a tear-off buys a longer, cleaner roof. If the existing roof is near end of life or shows any sign of deck problems, most roofers push toward a tear-off because an overlay just puts a new surface over a failing base.
When is a roof overlay actually allowed?
A roof overlay is allowed only when the roof already has a single layer of shingles and that layer is in sound condition. The 2021 International Residential Code bars a recover where the existing roof already has two or more applications of any roof covering (IRC R908.3.1.1, “Roof recover not allowed”), so if a second layer already exists, an overlay is off the table and a tear-off is required. The same section lists other conditions that force a full tear-off regardless of layer count.
Under 2021 IRC R908.3.1.1, a recover is not permitted when the existing roof or covering is water soaked or deteriorated to the point it is not adequate as a base for more roofing, when the existing covering is slate, clay, cement or asbestos-cement tile, or when the existing roof has two or more applications of any type of covering. Wood shake is not on that list. Section R908.3.1 item 3 lets metal panels, metal shingles and concrete or clay tile go over existing wood shake, and R908.4 requires the resulting concealed space to be covered with gypsum board, mineral fiber, glass fiber or another approved material. Whether asphalt shingles can go over shakes comes down to the shingle manufacturer’s instructions and your building department. (R908.5 in the 2021 IRC covers reinstallation of existing slate and tile, not tear-off triggers.) Section numbers can shift between code editions and some jurisdictions amend these rules, so the code edition your jurisdiction adopted and your permit office have final say.
- One existing layer, deck sound: overlay may be permitted.
- Two existing layers: tear-off required under 2021 IRC R908.3.1.1.
- Wet, rotted, or buckled decking: tear-off required, an overlay traps the problem.
- Slate, clay, cement or asbestos-cement tile underneath: tear-off required under 2021 IRC R908.3.1.1.
- Wood shake underneath: not a code tear-off trigger in the 2021 IRC, but the new covering must be allowed over shakes and R908.4 applies; check the manufacturer’s instructions and your permit office.
What does reroofing cost?
Reroofing cost depends on the method, the roof size, and the material. A tear-off and replacement with architectural asphalt shingles runs about $5 to $8 per square foot installed, per our 2026 roofing cost report, while the tear-off portion alone adds about $1 to $3 per square foot for asphalt and up to $5 per square foot for heavier slate or tile. An overlay typically lands 25 to 40 percent below a tear-off because it skips removal and haul-away.
Two cost drivers surprise homeowners. First, deck repair: a crew often cannot price rotted decking until the old roof is off, so a tear-off quote may carry a per-sheet allowance for replacing bad sheathing. Second, disposal: tear-off debris is heavy and dump fees vary by region, which is a large part of why overlays cost less. For a full breakdown of what goes into the number, see our guide to the cost to redo a roof and the itemized tear-off roof cost.
Why roofers often steer away from overlays
Roofers frequently recommend a tear-off over an overlay because an overlay hides problems and shortens roof life. Laying new shingles over old ones traps heat against the shingles, which accelerates granule loss, adds a full second layer of dead weight to the structure, and hides any decking rot, nail pops, or failing flashing underneath. It also makes future leaks far harder to trace because water can travel between the two layers before it shows up inside. For what that looks like on the finished roof, see how an overlay telegraphs through new shingles.
The lifespan gap is the clearest cost argument. An overlay averages around 16 years against 20 to 30 for a proper tear-off, so the money saved up front is often erased when the overlay fails a decade early and forces a mandatory tear-off anyway. An overlay can also reduce or void a shingle manufacturer’s warranty, because most warranties assume installation over a clean deck with fresh underlayment.
How to choose a re roofing company
A trustworthy re roofing company carries state licensing where required, real insurance, manufacturer certification, and gives you an itemized written quote that names the method, materials, and deck-repair terms. The single most useful filter is whether the company explains why it recommends an overlay or tear-off for your specific roof, rather than defaulting to the cheaper option to win the bid. Use the checklist below before you sign anything.
- Verify license and insurance. Confirm the state or county license (where required) and ask for certificates of general liability and workers’ compensation, then verify them with the carrier, not just the contractor.
- Confirm the method and code path. Ask whether they are quoting an overlay or tear-off, and why, and whether local code and your permit office allow an overlay on your roof.
- Get an itemized written quote. The bid should separate tear-off, disposal, underlayment, flashing, shingles, and a per-sheet deck-repair rate, not just a single lump sum.
- Check manufacturer certification. Certification from GAF, Owens Corning, or CertainTeed qualifies you for stronger workmanship warranties and signals trained crews.
- Read the deck-repair clause. Since rot is only visible after tear-off, the contract should state the price per sheet of replaced decking so a change order does not become a surprise.
- Compare three real bids. Line up at least three itemized quotes on the same scope so you are comparing the roof, not the sales pitch.
For the deeper vetting process, our 15-point roofing contractor checklist covers licensing verification, red flags, and contract clauses in detail. Treat any company that pressures you toward an overlay without inspecting for a second layer or checking the deck as a warning sign.
Reviewed by The Roofing Brief Team. Last reviewed: October 2026.
Frequently asked questions
What is reroofing?
Reroofing is installing a new roof covering on a building that already has one. It happens two ways: an overlay, where new shingles are laid over one existing layer, or a tear-off, where the old covering is stripped to the deck before new material goes on. A tear-off is a full replacement; an overlay is a faster, cheaper partial one that leaves the old layer in place.
Is a roof overlay cheaper than a tear-off?
Yes. A roof overlay usually costs about 25 to 40 percent less than a tear-off because it skips removing and hauling away the old roof. The savings are real up front, but an overlay lasts around 16 years versus 20 to 30 for a tear-off, so the lower price often disappears when the overlay fails a decade early and forces a full tear-off later.
How many layers of shingles are allowed on a roof?
The 2021 International Residential Code (IRC R908.3.1.1) does not permit a recover where the existing roof already has two or more applications of any roof covering, which in practice caps asphalt shingles at two layers. If your roof already has one sound layer, an overlay adding a second may be permitted. If two layers already exist, an overlay is not allowed and a tear-off is required. Local jurisdictions can amend this, so your permit office has the final say.
When is a tear-off required instead of an overlay?
Under 2021 IRC R908.3.1.1, a recover is not allowed, so a tear-off is required, when the existing roof is water soaked or deteriorated, when it is slate, clay, cement or asbestos-cement tile, or when two or more layers of any covering already exist. Wood shake is not on that code list, but the new covering must be approved for use over shakes. A tear-off is also the practical choice whenever the deck may be rotted, since an overlay traps that damage under a new surface.
How do I choose a good re roofing company?
Verify the company’s license and insurance directly with the carrier, confirm whether it is quoting an overlay or tear-off and why, and require an itemized written quote that separates tear-off, disposal, underlayment, flashing, and a per-sheet deck-repair rate. Favor manufacturer-certified crews and compare at least three bids on the same scope so you are comparing the work, not the sales pitch.
Does a roof overlay void the shingle warranty?
It can. Most shingle manufacturer warranties assume installation over a clean deck with fresh underlayment, so laying new shingles over an old layer may reduce or void warranty coverage. Trapped heat from the second layer also shortens shingle life. Always confirm warranty terms with the manufacturer and the roofing company in writing before choosing an overlay.