How to budget a roof replacement
What actually drives the cost of a roof replacement, how to compare quotes line by line, and how to set a realistic budget before you call a contractor.
A roof replacement is one of the largest single expenses a homeowner faces, and one of the easiest to overpay for, because most people get a single lump-sum quote and have no way to tell whether it is fair. The number on the quote is not arbitrary. It is built from the size of the roof, the material on it, the height and steepness of the house, how easy the crew can access it, and how much preparation the deck needs. Understand those inputs and you can read any quote line by line.
The figures in this guide are planning ranges, not bids. Labour rates, code requirements, and material prices vary by region and move with the market. Use them to build a realistic budget and to ask better questions, not to argue a contractor down to a number from a website.
The unit that matters: the square
Roofers do not price by the square foot. They price by the square, which is 100 ft² of roof surface. A 1,800 ft² roof is 18 squares. Almost every material and labour rate in the industry is quoted per square, so the first step in any budget is converting your roof to squares.
That conversion is not as simple as measuring the footprint of the house. The roof surface is larger than the floor plan because it slopes. The factor that corrects for the slope is called the slope factor, and it comes directly from the pitch.
The roof pitch calculator returns both the pitch (as x/12), the angle in degrees, and the slope factor. The slope factor is the square root of 1 plus the square of the rise-over-run ratio:
slope factor = √(1 + (rise ÷ run)²)
A 6/12 pitch rises 6 inches for every 12 inches of run, a ratio of 0.5. The slope factor is √(1 + 0.25) = 1.118. A 10/12 pitch has a ratio of 0.833 and a slope factor of 1.302. So a 1,500 ft² footprint carries about 1,677 ft² of roof at 6/12, but 1,952 ft² at 10/12 — roughly 16% more surface, and 16% more material, for the same house.
| Pitch | Angle | Slope factor | Roof area per 1,500 ft² footprint |
|---|---|---|---|
| 4/12 | 18.4° | 1.054 | 1,581 ft² |
| 6/12 | 26.6° | 1.118 | 1,677 ft² |
| 8/12 | 33.7° | 1.202 | 1,803 ft² |
| 10/12 | 39.8° | 1.302 | 1,952 ft² |
| 12/12 | 45.0° | 1.414 | 2,121 ft² |
Notice the second effect of pitch. Steep roofs do not just need more material; they are slower and more dangerous to work on, so labour rates rise too. The roofing cost calculator applies a 1.20 multiplier to labour for steep pitches on top of the larger area, which reflects both realities at once.
What drives the cost
Six inputs account for most of the variation between quotes:
- Roof area. More squares means more of everything, in near-linear proportion.
- Material. The single biggest swing. Asphalt shingles are the budget default; metal, tile, and cedar can each cost several times more.
- Height. A two-storey house usually carries a labour multiplier because of staging, ladder work, and fall protection; a three-storey or awkward-access roof more again. The calculator uses 1.00, 1.15, and 1.30.
- Pitch. Steep roofs cost more for area and more for labour, as above.
- Tear-off. Removing the old roof adds disposal and labour, typically $50–100 per square, plus dumpster fees.
- Complexity. A simple gable with few penetrations is fast. Hips, valleys, dormers, skylights, and chimneys add cutting, flashing, and time.
Anything that is not on that list still matters — underlayment, flashing, ventilation, deck repairs, and permits all show up in a real quote — but those six set the scale.
Material choices compared
Here are the material and labour ranges the calculator uses, expressed per square (100 ft²). Material costs are per square for the covering itself; labour covers installation. They are broad national-style ranges, and your local market may sit outside them.
| Material | Material per square | Labour per square | Typical service life |
|---|---|---|---|
| Asphalt shingles | $100–$200 | $150–$250 | Roughly 15–30 years |
| Metal | $300–$700 | $250–$400 | Commonly 40–70 years |
| Concrete / clay tile | $400–$700 | $300–$500 | Often 50 years or more |
| Cedar shake | $250–$400 | $250–$450 | Roughly 20–30 years with upkeep |
The cheaper covering is not automatically the cheaper roof. A material that lasts three times as long can win on cost per year even if it costs three times as much up front, and a heavier material may need structural review before installation. Metal and tile also shed heat differently and behave differently in hail and wind, which matters in some climates more than others.
Tear-off or layover
A layover installs new shingles directly over the old layer. It is cheaper and faster because there is no removal, no disposal, and no decking work. But it carries real trade-offs. Many building codes limit how many layers a roof may carry. Most shingle manufacturers will not honour a material warranty unless the old roof is removed, so a layover can quietly cost you the warranty. And because the deck stays hidden, any soft or rotted sheathing goes undetected and unfixed.
A full tear-off exposes the deck, allows damaged sheathing to be replaced, lets new underlayment and flashing go down properly, and is what nearly every manufacturer expects. It costs more, but it is the method that lets the roofer do the job correctly. When a quote offers a layover as the default, ask why and what it does to the warranty.
What sits under the shingles
The visible covering is only part of the assembly. Under it sit the underlayment, the flashing, and the ventilation, and these are where bargain quotes often cut corners.
- Underlayment. A water-resistant layer over the deck. Synthetic underlayment is generally more durable than traditional felt; the grade and coverage belong on the quote.
- Ice-and-water shield. A self-adhering membrane required in many cold climates at the eaves and in valleys, where ice dams and standing water are likely.
- Flashing. Metal pieces that seal the roof at chimneys, walls, valleys, vents, and skylights. Leaks cluster at these transitions, so the flashing detail matters more than the shingle brand.
- Ventilation. Intake and exhaust vents that move hot, moist air out of the attic. Poor ventilation shortens roof life, so a quote that omits ridge vent or intake vents is incomplete.
- Decking. The sheathing itself. If it is soft, delaminated, or thin, sheets get replaced during the job, usually priced per sheet.
Ask each contractor to name the underlayment product, the flashing approach, and the ventilation plan. Vague answers here are a better warning sign than a high price.
A worked budget
Run a typical job through the roofing cost calculator: 1,800 ft² of roof, asphalt shingles, two storeys, standard pitch, full tear-off, simple shape.
- Squares: 1,800 ÷ 100 = 18
- Material: 18 × $100 to 18 × $200 = $1,800–$3,600
- Labour: 18 × $150 × 1.15 to 18 × $250 × 1.15 = $3,105–$5,175
- Tear-off: 18 × $50 to 18 × $100 = $900–$1,800
- Total: about $5,800–$10,600, or $3.23–$5.88 per square foot
That range is wide because it should be. A quote at the bottom and a quote at the top are not necessarily better or worse; they may simply use a different shingle line, a different underlayment, or a different labour rate. The value of the range is that any quote wildly outside it deserves a question, and the line-item build shows you exactly which component to question.
Add a contingency on top. A roof often hides at least a little rot, and replacing even a few sheets of decking adds cost. Budget an extra 10–15% and treat it as expected rather than as a nasty surprise.
How to compare quotes line by line
Two quotes for the same house can differ by thousands and still be for the same job — or for very different jobs. To compare them fairly, put them side by side against the same checklist:
- Squares and measurement. Did each contractor measure the same roof the same way? A quote based on the footprint, not the sloped area, will look artificially cheap.
- Material brand, line, and colour. “Architectural shingles” spans a huge quality range. Get the exact product.
- Underlayment and ice-and-water membrane. Type and where it is applied.
- Tear-off and disposal. Is removal and dumpster hire included, or listed separately?
- Decking. What is the per-sheet price for replacement if rot is found?
- Flashing and ventilation. New or reused? Which components?
- Permits. Included, and who pulls them?
- Warranty. Separate the manufacturer’s material warranty from the contractor’s workmanship warranty, and note the length and what voids each.
- Payment schedule. How much up front, and how much on completion?
The quote with the most detail is usually the one worth taking seriously, even if it is not the cheapest. A single line reading “new roof — $9,000” tells you nothing about what you are buying.
Red flags
- A large deposit up front. A reasonable schedule ties most of the payment to completion. A demand for half or more before work begins shifts all the risk to you.
- No written, itemised quote. Verbal estimates cannot be compared or enforced.
- No licence, insurance, or local references. Ask for the numbers and verify them.
- Pressure to sign today, or claims that a price expires within hours.
- A price far below every other quote. Something is being left out, and it is usually the parts you cannot see.
- “We’ll skip the permit.” A permit protects you and the eventual resale; skipping it can make the work illegal and uninsurable.
- No workmanship warranty in writing. The material warranty is the manufacturer’s; the installation warranty is the contractor’s, and it is the one that covers leaks from poor work.
Paying for it
A roof is rarely an ideal candidate for a high-interest credit card, because it is a planned, large, and non-negotiable expense. The common routes are a secured home improvement loan, a home equity line of credit, or a contractor’s financing partner. Compare the annual percentage rate across offers rather than the monthly payment, and read whether any loan places a lien on the home. Beware of financing sold as “no interest for a year” if the rate afterwards is steep and the balance is large.
If cash flow is tight, it can be worth phasing the work: a full tear-off and deck repair on the most damaged elevation first, with the rest to follow, is better than a cheap layover everywhere that fails early. Talk to the contractor about what can safely be staged.
Frequently asked questions
How long does a roof last?
It depends heavily on material and climate. Asphalt commonly runs 15–30 years, metal and tile considerably longer, and cedar roughly 20–30 years with maintenance. Ventilation, sun exposure, and storm frequency all shift those figures.
Is a layover ever the right choice?
It can be a reasonable budget option on a sound deck with a single existing layer, especially if you plan to sell soon. But check local code limits, expect the manufacturer warranty to be affected, and understand that hidden deck damage will stay hidden.
Why is one quote so much higher than another?
Usually a different shingle line, a different underlayment or flashing specification, or a different labour rate rather than outright overcharging. Put the quotes side by side against the checklist above before assuming either is wrong.
How much should I hold back until the job is done?
Enough to matter. A common arrangement is a modest deposit, progress payments as materials arrive, and a meaningful final payment after inspection and cleanup. Never pay the full amount before the work is finished.
To plan your own budget, start with the roof pitch calculator to turn your footprint into true roof area, then run that area through the roofing cost calculator for a material-and-labour range. If siding is being done at the same time, the siding cost calculator follows the same area-and-waste logic and can help you compare a combined quote against two separate ones.