11/12 Roof Pitch

42.5 Degrees, 91.7% Slope and a 1.3566 Area Multiplier

What is a 11/12 roof pitch in degrees?

A 11/12 roof pitch is 42.5 degrees. It rises 11 inches for every 12 inches of horizontal run, which is a 91.7% slope and an area multiplier of 1.3566 — so a 2,000 square foot footprint at 11/12 is 2,713 square feet of roof.

A 11/12 roof pitch rises 11 inches for every 12 inches of horizontal run. That works out at 42.5 degrees, a slope of 91.7%, and an area multiplier of 1.3566 — so a flat footprint multiplied by 1.3566 gives the actual sloped roof surface you have to buy material for. Everything below is derived from that single ratio: the roof area at common house sizes, how many bundles of shingles it takes, whether the roof is walkable, and which coverings the code allows at this slope.

What 11/12 means in every unit

11/12 roof pitch converted
Unit	Value	What it is
Pitch	11/12	Rises 11 inches over 12 inches of run
Angle	42.5°	What a digital level or inclinometer reads
Slope	91.7%	Rise divided by run — used in drainage work
Area multiplier	1.3566	Multiply the footprint by this for the real roof area
Rafter length per foot of run	1.357 ft	Feet of rafter per foot of horizontal run

All four describe the same slope. Pitch is what a lumber yard, a truss plant and a code table use; degrees is what an instrument reads; the multiplier is the one you order material against.

Roof area and material at 11/12

Roof area, squares and bundles at 11/12 pitch
Footprint	Roof area at 11/12	Squares	Bundles at 10% waste	Bundles at 15% waste
1,000 sq ft	1,357 sq ft	13.6	45	47
1,500 sq ft	2,035 sq ft	20.3	68	71
2,000 sq ft	2,713 sq ft	27.1	90	94
2,500 sq ft	3,391 sq ft	33.9	113	118
3,000 sq ft	4,070 sq ft	40.7	135	141

A 11/12 roof adds 35.7% to the footprint area. On a 2,000 square foot footprint that is 713 extra square feet of covering — 7.1 squares you would not have ordered from the ground measurement alone.

Working on a 11/12 roof

Roof jacks or staging required — not casually walkable.

Standard asphalt shingle installation, with no low-slope underlayment requirement.

Waste factor: the usual allowance still applies — 10% for a simple gable, 15% for a hip roof, up to 20% for a cut-up roof. Pitch changes the area, not the waste rule.
Labour: work above 9/12 takes roughly twice as long per square as work at 4/12, because material has to be carried rather than slid and everything needs staging.
Ventilation: unaffected by pitch. The 1/300 rule is set by attic floor area, not by slope.
Rafter length: multiply the horizontal run by 1.4 to get the rafter, before adding the overhang.

How to confirm your roof is 11/12

Hold a 12-inch level against a rafter in the attic, bring it level, and measure straight down from the 12-inch mark. If the drop is 11 inches, the roof is 11/12.
A digital inclinometer on a rafter should read 42.5 degrees, within a few tenths.
A speed square with a pitch scale, held against a level, reads the ratio directly.
Round to the nearest standard pitch. Rafters and trusses are cut to whole increments, so ordering against an unrounded decimal produces a roof that does not meet at the ridge.

Frequently asked questions

What is 11/12 pitch in degrees?

A 11/12 roof pitch is 42.5 degrees. Take the arctangent of 11 divided by 12. The same slope is 91.7% and has an area multiplier of 1.3566.

What is the 11/12 roof pitch multiplier?

1.3566. Multiply the building footprint by 1.3566 to get the actual sloped roof area — a 2,000 square foot footprint at 11/12 is 2,713 square feet of roof.

Can you put shingles on a 11/12 roof?

Yes. 11/12 is above the 4/12 threshold, so standard shingle installation applies with no low-slope underlayment requirement.

Can you walk on a 11/12 roof?

Not casually. At 11/12 you need roof jacks or staging and proper fall protection — the angle is 42.5 degrees.