Two roof quotes, six thousand apart, both honest

You get three quotes for the same roof. One comes in at fourteen and change, one at just under twenty-one, one somewhere in between. The instinct is to assume the expensive one is padding and the cheap one is hungry.

Sometimes that's true. More often the two contractors walked the same roof and wrote down two different jobs, and neither of them explained that in a way you could see. Four line items account for most of the spread on a typical asphalt shingle replacement. Find those four and the quotes become comparable.

Line one

Tear-off, or new shingles over the old ones

Putting a new layer over an existing one skips the labor of stripping the roof and the cost of hauling it away. That's real money, and it's the single biggest reason one bid can be thousands under another.

It is also limited. Under the residential code, an overlay is not permitted where the roof already carries two or more applications of any covering, where the existing roof is water-soaked or deteriorated enough that it's a poor base, or over materials like slate, clay and asbestos-cement tile. Each layer of asphalt adds meaningful dead load, and some cold and snow-load jurisdictions amend the allowance down further. Your local building official has the final say, not the contractor and not this page.

The quieter cost is that an overlay puts new shingles on top of a deck nobody has looked at. Soft sheathing, old nail holes, a slow leak around a vent, none of it gets found. It also tends to shorten the life of the new shingles, because they sit on an uneven surface and run hotter.

A quote should say plainly which one it is. If it says "install new shingles" and nothing about removal or disposal, ask.

Line two

The decking allowance, and who decides

Once the old roof is off, some sheets of sheathing will be bad. Nobody can tell you how many from the driveway. So quotes handle it with an allowance, and the allowance is where budgets quietly move.

The versions you'll see: no mention at all, which means it's a change order at whatever rate they name on the day. Or "decking replaced as needed," open-ended in both directions. Or the version you want, which reads something like five sheets of 7/16 OSB included, additional sheets at a stated price per sheet.

Two things make that line safe. The first is the unit price, so a surprise has a ceiling you can do arithmetic on. The second is a rule about who confirms it. Photographs of the bad sheathing before it's covered, and a call to you before the count goes past what's included, costs the contractor nothing and removes the entire argument.

Line three

How far the ice barrier actually runs

In cold climates the code requires a self-adhering membrane, or two cemented layers of underlayment, along the eaves. The requirement is not "a row at the bottom." It runs from the lowest edge of the roof to a point at least 24 inches inside the exterior wall line, measured horizontally.

That measurement is why the drawing above matters. The reach you need is the overhang plus 24 inches. A house with a two-foot overhang needs roughly four feet of coverage, which is two courses of standard 36-inch membrane, not one. A quote that budgets a single course on a deep overhang has priced a roof that may not pass inspection, and more to the point has left the weakest part of the assembly short.

Beyond the minimum, valleys, skylights, chimneys and low-slope sections are all places a careful contractor adds membrane and a cheap one doesn't. That's a legitimate difference in scope, not padding, and it should be written down either way.

Line four

New flashing, or the old flashing put back

Roofs almost never fail in the middle of a slope. They fail where the roof meets something else: a wall, a chimney, a plumbing vent, a valley.

Reusing existing step flashing and pipe boots saves a few hundred dollars in materials and a good deal of labor, because new step flashing means pulling back siding and weaving each piece into the courses. It's the difference between a job that lasts as long as the shingles and one that gets a leak at the chimney in year six. Drip edge is worth checking too; it's required at eaves and rakes, and it's a common omission on the thinnest bids.

Ask specifically: new step flashing, new counter-flashing at the chimney, new pipe boots, new drip edge. Four yes-or-no answers.

Worked example

The same roof, priced two ways

Here is what those four lines look like side by side on a hypothetical 28-square roof. The dollar figures are illustrative and exist to show the shape of the gap, not to price your job.

Quote A is not a scam. It is a cheaper, shorter-lived roof with more unknowns left in it, and for a house you're selling in two years that might be the correct purchase. The problem is that nothing in the number tells you that, and most homeowners are comparing the numbers.

Before you sign

Six questions that make quotes comparable

The material warranty comes from the shingle manufacturer and covers defects in the shingle. The workmanship warranty comes from the contractor and covers the installation, which is what actually fails. They are not the same thing and a quote that advertises "lifetime warranty" is usually talking about the first one.

Get those six answers in writing from everyone bidding, and you stop comparing three numbers. You start comparing three jobs, which is the only comparison that means anything.

Code references describe the International Residential Code as commonly adopted; your jurisdiction may amend it, and your local building official's interpretation governs. Written for homeowners and offered as general guidance only. It is not a substitute for a written, itemized proposal from a licensed contractor or for an on-site inspection.