Compare the Measuring Tool Behind Each Roof Number

A roof bid starts with a number most homeowners never see being made. Somebody walks your lawn with a tool, or sits at a desk with an aerial image, and produces the square count that every price on the page multiplies. One square is 100 square feet of roof surface, so a small error in the count becomes a large error in the total. Before you put two bids side by side, find out what produced each number.

Roofer comparison: the measurement method

Roofers measure in a few common ways. Some walk the roof with a tape or a measuring wheel and sketch each plane. Some use a laser distance meter from the ground or from a ladder, which works well on simple gables and struggles on hips with many short planes. Some order an aerial or satellite measurement report from a vendor and then adjust it by eye. Some use a drone. Each method can produce a good number. The problem comes when a bid does not say which one it used, because then you cannot judge the number at all.

A St. Louis house adds its own trouble. Older homes in the city and in the county often have a dormer on one side, a bay window roof tied into a main hip, and a porch roof that meets the wall at an odd angle. Aerial images can miss a small shed dormer under a tree canopy. A ground measurement can miss a low porch roof the crew never climbs. When two bids come from two methods, the gap between them may be the method, not the roof.

What the tool itself tells you

A laser distance meter is only as good as its last check. Most can be verified against a known length, and a tool that has been dropped off a truck bed may read a few inches off over a long run. A roofer who knows the tool's history can tell you when it was last checked against a tape or a marked line. A roofer who has never thought about it will often say the tool is "accurate," which tells you nothing about how accurate.

The same question applies to pitch. A steep plane has more surface than its footprint on the ground, so a bid that measures footprint and does not convert by pitch undercounts a steep house. Ask which pitch the bid used for each plane and whether the number on the page is the flat footprint or the true sloped surface.

Check the count roughly on your own

You do not need a laser to catch a large error. Measure the eave length of each side of the house with a tape, or pull the lot dimensions from a public parcel map if they are listed. Then compare the roof's plane count and ridge length against the roofer's diagram. A hip roof with four planes on the diagram should look like four planes when you stand in the yard. If the diagram shows a shed dormer that does not appear from the street, ask where it came from. A few minutes with a tape and a sketch will not replace a proper measurement, but it will show you whether a bid sits in the right range or in a different house's range.

What it costs when the count is off

Roofing bids usually price by the square, sometimes with materials, labor, underlayment, starter, ridge, and disposal each carrying its own quantity. If the square count is high by five squares, every one of those lines inflates with it. A count that is low by five squares leaves a gap that shows up later as a change order, usually after the old roof is already off and the homeowner has the least room left to compare alternatives.

Ask each roofer for the measured area, the waste allowance added on top, and the final shingle order in squares. A bid that shows measured area, a visible waste line, and an order quantity lets you check the arithmetic yourself. A bid that shows only a price per square with no count leaves you guessing at both. Waste is a real allowance for cuts, hips, and valleys, so a small addition is normal. An unexplained jump is not.

If you want to check our own count, Keys Roofing will walk through how we measure at (314) 220-2333. A roofer who is willing to show the planes and the arithmetic should be willing to answer these questions from any homeowner on the list.

What to ask each roofer

• What method produced the square count on this bid: walk, tape, laser, aerial report, or drone?
• If a laser meter was used, when was it last checked, and against what?
• Does the count convert sloped planes to true surface area, or does it show footprint only?
• Which planes were measured on the roof, and which were estimated from the ground or from an image?
• What waste allowance was added, and what is the final shingle order in squares?
• Will you give me the measurement sheet or diagram with my bid?
• If the permit drawing measures the roof differently, which number governs the price?

How to read the answers

Write each answer next to the bid it belongs to. A roofer who names a method, gives a date for the tool check, and hands over a diagram has given you something you can compare. A roofer who says the number came from experience has given you a number and an opinion. Neither is automatically wrong, but only the first lets you find the error if there is one.

If two bids differ by more than a few squares, do not split the difference. Ask each roofer to show the planes they measured and compare plane by plane. Most gaps come from a dormer, a valley, or a porch roof that one measurement counted and another skipped. Once you see which plane is missing, the decision becomes a question about that plane, not a guess about which company sounds more confident.

Keep each roofer's diagram side by side with the other. A plane that appears on one sheet and not the other is a question you can put to both companies in writing, and the answer belongs in the same file as the sheet it refers to.