The Takeoff The multiplier

Pitch, and what it does to the number twice

Slope is the only variable on a roof that raises the cost through two separate doors at once. It puts more surface on the house, and then it makes that surface harder to stand on. Most quotes account for the first and quietly guess at the second.

Pitch is written as rise over run: inches of vertical rise for every twelve inches of horizontal run. A 4:12 roof climbs four inches in a foot. A 12:12 roof climbs twelve, which is forty five degrees. In St. Louis housing stock you will meet almost everything between about 3:12 on a mid century ranch addition and 12:12 or steeper on a Victorian or a steep gabled Tudor in the older suburbs.

Door one: the surface

The slope factor is a right triangle and nothing more. Rise over twelve, squared, plus one, square rooted. Here is the table, exact to three decimal places, applied to a single flat one thousand square feet of footprint so the effect is legible.

Slope multiplier, and the roof surface over 1,000 square feet of footprint
Pitch	Multiplier	Surface	Working on it
3:12	1.031	1,031 sq ft	Walkable, low slope caution
4:12	1.054	1,054 sq ft	Walkable
5:12	1.083	1,083 sq ft	Walkable
6:12	1.118	1,118 sq ft	Walkable, care in the wet
7:12	1.158	1,158 sq ft	The line. Staging usually starts here
8:12	1.202	1,202 sq ft	Roof jacks and toe boards
9:12	1.250	1,250 sq ft	Staged, slower
10:12	1.302	1,302 sq ft	Staged throughout
12:12	1.414	1,414 sq ft	Fully staged, specialist pace

Read the last row again. A 12:12 roof carries forty one percent more surface than the ground it covers. On the footprint above that is more than four extra squares of material, underlayment, nails, labour and disposal, on a house that from the street looks the same size as its neighbour.

Door two: the labour

Somewhere around seven inches of rise in twelve, a roof stops being a floor and starts being a wall. The exact point depends on the person, the shoe, the weather and what the old surface is doing, but the working consequence is consistent: past that line a crew can no longer move about freely, carry bundles by hand or set their feet without thinking about it.

What enters the job at that point is staging. Roof jacks are brackets nailed through the deck to carry a plank, and the crew works off the plank and moves it up the slope as the courses go on. That is slower in three ways. The jacks have to be set and struck. The material has to be moved in smaller lifts. And every course takes longer to lay because nobody is standing casually.

The question that catches a guessed quote

Ask what pitch was measured, and ask how. A person who went up with a pitch gauge or a level and a ruler will tell you the figure without pausing. A number produced from a screen will usually come back as a range, or as a description of the house rather than the roof. That is the moment you learn whether five of your seven variables were measured or assumed.

Steep downward view across a newly laid grey and charcoal architectural shingle roof taken by a person standing on it, whose forearm, metal wristwatch and knee intrude into the frame at the left and bottom. Running along the left is the adjoining lower roof still covered in old brown three tab shingles with their small even rectangular tabs, and beyond it a yellow vinyl sided house, a winter lawn and a street with parked cars. — **Plate 03** Taken standing on the plane, which tells you this one is comfortably walkable. The photographer's own arm and knee are in the frame. Note the two surfaces: new dimensional architectural shingles on the right, old flat three tab on the adjoining roof at the left, with its small even rectangles.

Low slope has its own problem

Below about 4:12 the difficulty inverts. There is barely any extra surface to buy, and the roof is easy to stand on, but water moves off it slowly and wind can drive it back up under the courses. Manufacturers publish specific low slope requirements, generally involving doubled underlayment, and below roughly 2:12 asphalt shingles are the wrong product altogether.

Low slope also has a permitting consequence in St. Louis County, where a like for like asphalt replacement on a slope of 4:12 or steeper generally needs no permit, while a shallower slope generally does. Municipalities layer their own rules on top of the county, and some, Ballwin and Kirkwood among them, run their own contractor licensing as well. Confirm with the building division for your own address before the dumpster arrives rather than after.

Why the same house can carry two multipliers

Additions are the usual culprit. A porch roof or a rear addition is frequently built shallower than the original house, because it had to tuck under an existing wall or window line. So a single property can need two multipliers and two sets of low slope detailing, and a takeoff that applied one number to the whole outline has already gone wrong before the material was priced.

Measured, then quoted

Have someone actually measure the pitch

Pitch is a two minute measurement and it changes the material count and the labour rate at the same time. A takeoff from Keys states the slope it used, plane by plane, so the number you are given can be checked rather than believed.

If you would rather talk it through, this is the office line and not a call centre.

(314) 220-2333

Keys Roofing, greater St. Louis