Repair or replace: the questions that actually decide it
The size of the damage is the least important input. Age and layers decide most of these.
At some point the diagnosis is settled and a different question arrives. It is a large decision made infrequently, usually under some pressure, and often with one quote and no framework. This page is the framework.
Question 1: how old is the roof?
This matters more than what is wrong with it, and it is the input most people do not have. A sound repair on a roof with fifteen years left is money well spent. The identical repair on a roof with two years left is money spent twice.
Establishing the age is usually possible without guessing, and it has its own article. The rough guide most people work with is that a standard asphalt roof in a moderate climate has a couple of decades in it, with a wide spread either side depending on the product, the climate, the slope, the colour and — often decisively — whether the attic was ventilated. A roof baked from underneath for fifteen summers is older than its years.
Question 2: how many layers are up there?
This one frequently decides it outright. Going over an existing roof — an overlay, or a re-cover — skips the tear-off and the disposal. It is faster and it costs less. It also brings real trade-offs:
- Nobody sees the deck. The single opportunity to find rot, delamination or previous water damage in the sheathing is while it is uncovered, and an overlay passes it up.
- It runs hotter. Two layers of asphalt hold more heat than one, and heat is what ages shingles, so the new covering will not last as long as the same product laid on a bare deck.
- Flashing details get harder. Working new flashing into a chimney or a valley over a raised, uneven surface is more difficult to do properly.
- Weight. It adds up, and the structure was designed for a number.
- Layer limits. Many jurisdictions cap how many layers a roof may carry, and permits reflect that.
The practical upshot: if a roof has been overlaid once already, the decision is generally made for you. Whether there is more than one layer can often be seen at the rake edge from the ground, or at the eave from a ladder.
Question 3: is the damage local or general?
A repair makes sense when the problem has a boundary. One failed flashing detail, a limb strike over a defined area, a valley that has worn out on an otherwise sound roof — these are repairs, and treating them as a reason to replace is overselling.
A repair makes less sense when the same failure is appearing everywhere. Curling across all slopes, granule loss with bald patches across the field, several leaks in unrelated places, shingles coming off in every storm. Those are not damage events, they are a roof reaching the end, and patching is buying months.
Question 4: what is the deck likely to be like?
The deck is the plywood or boards under everything, and it is invisible until a tear-off. Soft, delaminated or rotten sheathing found on the day is normal and expected rather than a disaster — but it changes the number, which is why it is worth knowing about in advance rather than at ten in the morning with the roof open.
Ask, before work starts, how deck replacement is handled: is a quantity allowed for in the quote, what is the rate beyond that, and who decides what needs replacing. A quote that is silent on this is a quote that will be revised.
Reading the quotes
You will not find prices on this site — roofing costs vary so much by region, pitch, access, season and material that a figure written here would mislead rather than help. What you can do is make sure you are comparing the same job.
Things that should be explicit: whether it is tear-off or overlay, how many layers come off, what underlayment is being used and where, whether an ice-and-water membrane is included at the eaves and valleys, whether flashing is being replaced or reused (this is a common and consequential difference), whether the drip edge is new, what happens at the vents, how deck repair is priced, who pulls the permit, how disposal is handled, and how the property is protected.
On warranties, the thing to understand is that there are usually two separate promises from two separate parties: the manufacturer covers the material, the contractor covers the workmanship. Most failures in the first years are workmanship, and a strong material warranty from a company that will not be there in three years is not much comfort.
And the permit
A roof replacement generally needs one. It is not a formality to be economized on: the permit is what brings an inspection, and the inspection is the one independent check on work that will be invisible within a day. A contractor who suggests skipping it is telling you something about how they work.
Overlay or tear-off
| Overlay (re-cover) | Tear-off | |
|---|---|---|
| The deck gets inspected | No — it stays hidden | Yes, and it is the only chance |
| How it ages | Hotter, so faster | As the product is rated |
| Flashing details | Harder to do properly over a lump | Done from the deck up |
| Weight | Adds to the structure | Back to one layer |
| Layer limits | Many jurisdictions cap them | Not an issue |
| Time and disposal | Less of both | More of both |
The uncomfortable part
Sometimes the correct answer is a repair on a roof that will need replacing in three years, because that is what is affordable now. That is a legitimate decision. What makes it a good one rather than a bad one is knowing that is what you are doing, rather than being told the repair has solved it.
Frequently asked questions
Is it worth repairing an old roof?
It depends on how old. A sound repair on a roof with fifteen years left is money well spent; the same repair on a roof with two years left is money spent twice. Establishing the age is more important than assessing the damage.
Can I just put a new roof over the old one?
Sometimes, and many jurisdictions cap the number of layers. The trade-offs are real: nobody inspects the deck underneath, two layers run hotter so the new covering ages faster, flashing is harder to do properly over an uneven surface, and the weight adds up.
How do I know if the deck needs replacing?
You generally cannot until the tear-off, which is why it should be priced in advance. Ask how much deck replacement is allowed for in the quote, what the rate is beyond that, and who decides. A quote silent on this is a quote that will be revised.
What should I compare between quotes?
That they are the same job: tear-off or overlay, layers removed, underlayment and where, membrane at eaves and valleys, whether flashing is replaced or reused, new drip edge, deck repair pricing, permit, disposal and property protection. Flashing reuse is a common and consequential difference.
Do I need a permit for a roof replacement?
Usually yes, and it is worth having rather than avoiding. The permit is what brings an inspection, and that inspection is the only independent check on work that will be invisible a day later.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- NRCA. National Roofing Contractors Association
- US OSHA. 1926.501 — Duty to have fall protection (OSHA)