Understanding your result
The headline is the days on site, with the worker-hours, the crew and the weather allowance. The stats give the worker-hours, the crew days and the days with weather; the breakdown builds each line.
The hours are the same as the labor cost calculator uses, so the two agree; the days feed the project schedule, which puts dates on them. Homeowners should multiply the hours as the DIY calculator does.
How we calculate this
Tear-off is 0.4 hours per square per layer for asphalt and 1 hour for tile and slate. The safety guide explains why steep roofs take longer.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Hours per square | by material, as in the labor calculator | Roofing estimating practice |
| Tear-off | 0.4 h (asphalt), 1 h (tile, slate) per square per layer | Estimating practice |
| Crew | 4 | A typical residential crew |
| Day | 8 hours | Standard |
| Weather | 20% | A judgement for spring and autumn |
| Setup | 4 hours per worker per job | Estimating practice |
Assumptions last reviewed October 7, 2026.
The calculator does not include waiting for materials or inspections. The pricing guide sets the hours against the price.
Two worked examples
An architectural reroof
24 squares, walkable, one storey, one layer, crew of 4.
- Install 26.4 h; tear-off 9.6 h; setup 16 h; total 52 h
- Crew days: 1.63; with 20%: 2 days
Slate on a steep two-storey house
24 squares, steep, two storeys, crew of 5.
- Install 205.9 h; tear-off 34.3 h; setup 20 h; total 260 h
- Crew days: 6.51; with 20%: 8 days
Where to find your inputs
Squares. From the shingle or roof area calculator.
Crew and day. From the contractor.
Weather. From the season.
Common mistakes
- No weather allowance. Rain stops tear-off.
- Days without setup. Deliveries and cleanup take time.
- Shingle hours for tile. Heavy materials take longer.
- Ignoring pitch. Steep is slower.
- Huge crews on small roofs. Diminishing returns.
- DIY at pro speed. Multiply by 3 to 4.
Questions people ask
- How long does it take to replace a roof?
- A crew of four reroofs a typical 24-square walkable asphalt roof with one layer off in about two days with a 20 percent weather allowance: about 36 worker-hours of tear-off and installation plus setup and cleanup. Steep, high or heavy roofs take several times longer.
- How many squares can a crew do in a day?
- On a walkable shingle roof a crew of four installs about 20 to 25 squares a day without tear-off and 15 to 20 with it. Standing seam, tile and slate are two to six times slower.
- How much time should I allow for weather?
- 20 to 30 percent in spring and autumn, less in a dry summer. Roofs are not torn off when rain is forecast, and high wind and heat stop work too.
- Does a bigger crew finish faster?
- Up to a point: more workers shorten the days, but setup, deliveries and inspection do not shrink, and on a small roof a large crew gets in its own way. The calculator scales setup with crew size.
- How long does a tile or slate roof take?
- A 24-square slate roof on a steep two-storey house is about 260 worker-hours: eight days for a crew of five with a weather allowance.
- Is the time the same for DIY?
- No. Homeowners take three to four times a professional crew's hours; the DIY calculator applies that.