Roof replacement cost

Ask three roofers for a price and you will get three numbers with the same shingle on them. The spread is almost never the material. It is these four things, in roughly this order.

Pitch. Above about 8:12 nobody is walking on the roof. Staging, roof jacks and harnesses turn a two-day job into a four-day one, which is why crews add a steep-pitch surcharge — around 18% at 8:12, and climbing sharply from there. The calculator includes it and shows the percentage.

Layers. Every layer coming off is a full extra pass over the whole roof, plus its own weight in disposal.

Complexity. Dormers, valleys, skylights and chimneys are slow. A twenty-square cut-up roof takes longer than a thirty-square gable, and any estimate based purely on area will be wrong on both.

Access. A two-storey house on a narrow lot with no room for a dumpster near the eaves costs more than the same roof on a corner plot, and no calculator can see that from your inputs.

Only the labour half of the figure here moves with where you live. The shingles cost much the same in Mississippi as in New Jersey; the crew does not. The regional index table shows exactly what factor is being applied to your state and why it is applied only to labour.

Pitch is written as rise over run — the inches a roof climbs for every twelve it travels horizontally. It is the same thing as slope, and it converts to an angle in degrees, which is why the same roof gets described three different ways by three different trades.

The multiplier that turns footprint into roof area is not a table someone compiled. It is the hypotenuse of a right triangle whose base is 12 and whose height is the rise, divided by 12. Everything in the chart below is that one calculation.

Roofing does not use square feet. It uses squares — 100 ft² of roof surface — and every price you are quoted, from shingles to labour to stripping, will be per square. A quote of “$450 a square” is meaningless until you know how many squares the roof is, which is most of the reason estimates are hard to compare.

Shingles come in bundles sized so that three of them cover a square: 33.3 ft² each. That is not a coincidence, it is a packing decision — three bundles is about as much as one person carries up a ladder in a day without regretting it. Heavier designer shingles break the rule and run four bundles to the square, which is exactly the kind of assumption that leaves a roof one bundle short.

On a roof, waste is not a vague allowance for clumsiness. It is a direct consequence of geometry: every hip and every valley cuts shingles on the diagonal, and a shingle cut on the bias leaves an offcut that fits nowhere else.

So the allowance follows the shape, and the calculator sets it from the roof style you pick — with the reasoning printed beside it and an override if you disagree.

Shingles are what people price. The things that make the roof work are the lines that get left off the estimate, and together they are a meaningful fraction of the material bill.

Underlayment is the secondary water barrier over the deck. Synthetic comes in 10-square rolls, is lighter to carry and does not tear in wind before the shingles go on; felt is cheaper, heavier, and wrinkles if it gets wet. Below 4:12 the code wants it doubled.

Starter strip goes along the eave under the first course. Its adhesive is positioned to seal the bottom edge of the first row of shingles — cutting up regular shingles to do the job puts the sealant in the wrong place, and the first row is exactly where wind gets under a roof.

Hip and ridge cap is a thicker, pre-bent shingle for the ridges and hips. One bundle covers about 20 linear feet.

Drip edge is formed metal at the eaves and rakes that carries water off the deck edge and into the gutter instead of behind it. It comes in 10 ft pieces, it is required by code on most roofs, and it is the single most commonly omitted item in a homeowner’s material list.

Nails, finally, at four per shingle — about 320 to the square — or six in high-wind zones, which is 480. That is not a detail: nailing pattern is the most common reason a manufacturer denies a wind warranty claim.

Tear-off is the part of a re-roof that homeowners have no intuition for, because nothing about it scales the way the rest of the job does. It is priced per square and per layer, and disposal is priced by weight.

A square of architectural shingles weighs about 240 lb. A thirty-square roof with one layer coming off is therefore around three and a half tons of material that has to be lifted off a roof, carried down, and paid for at a transfer station by the ton. Two layers is seven tons, and it needs a bigger container or a second drop.

The honest summary: roofing over is cheaper now and more expensive later, and the saving is borrowed from the next re-roof. Where it is genuinely reasonable is a sound single layer on a simple roof that is being sold in the next few years. Where it is a bad idea is anywhere the deck is suspect — and a roof that was already covered over once usually was for a reason.

It is the commonest question anyone asks before re-roofing, and both sides answer it with a brochure. Here are the two figures from the same roof — 40 × 28 ft at 6:12, old roof stripped, worked out by the metal roof calculator and by this one.

Metal is 79 per cent more on this roof, and roughly level once you divide by the years. That is the honest version, and it is less flattering to metal than the industry’s and less flattering to shingles than a builder’s.

The catch is that you only collect metal’s extra life if you are there for it. A roof that outlasts you by thirty years is worth something to whoever buys the house and nothing to your own arithmetic — and the median American owner moves long before a shingle roof wears out, let alone a metal one.

So the real decision is not cost per year. It is: are you staying, is the roof simple enough that a metal crew will quote it sensibly, and do you care how it looks? Those three answer it. The per-year figures are close enough to be a tie.

Three code requirements matter enough to check before ordering, because none of them are preferences.

Minimum slope. Asphalt shingles are not permitted below 2:12 at all — that roof needs a membrane system. Between 2:12 and 4:12 they are allowed only with a doubled underlayment, which means twice the rolls the calculator shows.

Fastening. The number and placement of nails is specified, and six nails per shingle is required in high-wind areas. Manufacturers tie their wind warranty to it, so an under-nailed roof is both a code issue and an uninsured one.

Ice barrier. In freezing climates a self-adhering membrane is required from the eave to a defined distance inside the exterior wall line. The distance depends on your local amendment, which is why it is not in the quantities above.

Where a local amendment and this page disagree, the amendment wins. Everything here is residential practice under the model code, not a substitute for what your building official will actually inspect.

One caveat worth reading. Eave and rake lengths are computed exactly for gable and shed roofs, where a rectangle determines them. For hip and complex roofs the ridge, hip and valley lengths are estimated from the area, because a footprint alone does not determine them — and the result panel says so rather than presenting the estimate as a measurement. Before ordering ridge cap for a hip roof, walk it with a tape.

Bundle coverage comes from the manufacturer’s data sheet, slope and fastening rules from the model residential code, and prices from a survey split into material, labour, tear-off and disposal so each can be checked on its own. All of it is listed on the sources page with the date it was last checked.

Nothing you type is sent anywhere — the whole calculation runs in your browser.

Roofing has more trade vocabulary than any other material on this site, and quotes are written in it.