Calculators
Roof planning calculators
Lifespan and cost per year, when to replace, weight on the structure, solar fit, project scheduling and skylight sizing.
Before the material and the quote come the questions that decide whether to reroof at all: how long the present roof has left, whether a repair buys enough years to be worth it, whether the structure can carry a heavier material, and whether the new roof should be made ready for solar panels while the shingles are off. These calculators put numbers on those questions using published life expectancies, material weights and the setback rules in the fire code.
They are planning tools. The lifespan figures are ranges from building-industry surveys, not predictions about your roof; the weight calculator reports the load and tells you when an engineer should look at it; the solar calculator counts panels that fit, not the electricity they would make.
6 calculators
Roof Lifespan & Cost per Year Calculator
What a roof costs per year of life, with maintenance, compared with another material, from installed cost and expected life.
Roof Replacement Planner
The expected replacement window for a roof from its install date, material, climate, ventilation and the warning signs you can see.
Roof Weight Calculator
The dead load a roofing material puts on the structure, the change from the roof it replaces, and when an engineer should look.
Solar Panel Roof Fit Calculator
How many solar panels fit on a roof face after fire-code setbacks, in portrait or landscape, and the system size in kW.
Roofing Project Schedule
Finish date, book-by date and the order of work for a reroof from the start date, squares, material, crew and weather days.
Skylight Size Calculator
How much skylight glazing a room needs by daylighting rule and which standard sizes fit between your rafters.
Guides for this topic
Cedar shakes and shingles: exposure, bundles and lifespan
A bundle of cedar does not cover a fixed area: it covers more at a longer exposure. The Bureau's rule makes the count simple once that is clear.
Repair or replace: the signs, the maths and the timing
A leak does not always mean a new roof, and a dry ceiling does not mean the roof is fine. Age, signs and a simple sum decide it.
How long roofs last, by material
Every roofing material has a typical life, and every roof has a climate, an attic and an installer that move it. Here are the ranges and what to do with them.
Is your roof solar-ready? Area, pitch, setbacks and panels
Solar panels last 25 years or more. Before they go up, the roof under them needs to last as long, have room after the setbacks and face the right way.
Standing seam vs exposed fastener: quantities, cost and life
Both are metal roofs; they are built, priced and maintained differently. The difference shows up in the screws.
Tear-off: layers, weight, dumpster size and disposal cost
Tear-off is the messy line on a roofing quote. It is also the easiest to estimate, because roofing debris is all about weight.
Tile and slate: pieces per square, weight and what the structure must carry
Tile and slate last a lifetime and weigh three to five times as much as asphalt. Here is the count, the load and when the framing needs a second look.
Questions people ask
- How long does a shingle roof last?
- Industry life-expectancy surveys put three-tab asphalt shingles at 15 to 20 years and architectural shingles at 25 to 30, shorter in hot climates and under trees, longer with good ventilation. Exposed-fastener metal runs 30 to 45 years and standing seam 40 to 70, concrete tile 40 to 60, clay tile 50 to 100, slate 75 to 100 or more, and cedar shakes 25 to 30 with maintenance.
- Should I repair or replace my roof?
- Divide the repair cost by the years it will reliably buy and compare that with the replacement cost divided by the new roof's life. A $1,500 repair that buys 3 years costs $500 a year; a $14,000 roof that lasts 28 years costs $500 a year too, and leaves you with a new roof. The calculators in this group do both sides of that sum.
- How much does a tile roof weigh?
- Concrete tile weighs about 900 to 1,100 pounds per square installed and clay tile 600 to 1,000, against 230 to 430 for asphalt shingles. On a 25-square roof that is 11 to 14 tons of concrete tile, 9 to 10 pounds on every square foot of roof, and a structure framed for shingles must be checked by an engineer before it carries that.
- How many solar panels fit on my roof?
- A typical residential panel is about 65 by 40 inches, 18 square feet. After the fire code's 36-inch setbacks at the ridge and along the sides, a 40 by 15 foot south-facing roof face holds around 24 panels in portrait, about 9.6 kW at 400 watts each. The solar roof fit calculator lays the grid out for your face and setbacks.
- How long does a roof replacement take?
- A crew of four tears off and reshingles about 20 to 25 squares of walkable asphalt roof in a day; a steep or cut-up roof halves that, and tile, slate or standing seam take two to four times as long. A typical 25-square shingle roof is one to two working days plus weather. The project schedule calculator works the dates out for your crew and material.
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