Shed Roof Pitch: Chart, Minimums and Calculator

Shed roof pitch is how steep the roof is, written as inches of rise for every 12 inches of run, so 4/12 or 6/12. It decides what roof covering you can use, how tall the shed ends up, how long the rafters are and how the roof handles snow. This guide gives you the chart, the minimum pitch for shingles and for metal, and a calculator.

The numbers come from the shed designer and from the 2021 International Residential Code, the model code most states start from. The rafters themselves, with the plumb cut, the birdsmouth and the tail, are in the shed rafters guide. This page is about choosing the pitch before you cut anything.

What shed roof pitch means

Pitch is a ratio. Run is a horizontal distance, rise is how far the roof climbs over it, and the ratio is always quoted per 12 inches of run.

Rise over 12

A 4/12 roof climbs 4 inches for every 12 inches it runs. Read it as “four in twelve”. To find the total rise of a roof, multiply the run by the pitch and divide by 12. A 72 inch run at 3/12 rises 72 x 3 / 12 = 18 inches. A 60 inch run (half of a 10 ft wide gable shed) at 6/12 rises 60 x 6 / 12 = 30 inches. The rise is measured up from the top of the wall, so it adds to the wall height for the total height of the shed.

Pitch in degrees and percent

Some roofing rules and most phone levels use degrees. Others use percent slope. All three describe the same roof, and the conversion is plain trigonometry: the angle is the arctangent of rise over 12, and the percent slope is rise over 12 times 100. The 2021 IRC uses this pairing when it says 2:12 is a 17 percent slope and 4:12 is a 33 percent slope.

Only the first five are pitches the designer draws. The 8/12 row is here for reading a plan from somewhere else: the designer does not offer 8/12 or anything above 6/12.

From degrees back to a pitch

To go the other way, take the tangent of the angle and multiply by 12. A 22.5 degree slope gives tan 22.5 x 12 = 4.97, which is a 5/12 roof for every practical purpose. A 10 degree slope gives 2.12, just over 2/12. A 15 degree slope gives 3.22, a little steeper than 3/12. If your level reads in degrees, that is all you need.

Shed roof pitch chart from the designer

The designer draws a gable roof at 4/12, 5/12 or 6/12 and a lean-to (single slope) roof at 2/12, 3/12 or 4/12. The default is 6/12 for a gable and 3/12 for a lean-to. Nothing steeper is offered, so if you want 8/12 you will have to frame it by hand and skip the designer’s cut list.

The tables below are the designer’s results for four sheds with the default walls (88-3/4 inches on a gable shed, a 97-1/8 inch front wall on a lean-to), a 6 inch overhang and rafters 16 inches on center. Edge length is the length along the top of the rafter. The board column is the length of lumber needed once the plumb cut is included.

Gable shed pitch chart: 8x10 and 10x12

Overall height is measured from the ground. Going from 4/12 to 6/12 adds 7-13/16 inches to the 8x10 and 9-13/16 inches to the 10x12. The rafters grow by less than 4 inches, because the slope is only a little longer than the run. Either shed still buys 2x6 rafters at every pitch: 18 for the 8x10, 20 for the 10x12.

Lean-to pitch chart: 8x6 and 10x8

A lean-to has a tall front wall and a low back wall, and the rafters run from front to back. The designer keeps the front wall at 97-1/8 inches and lets the back wall drop, so the pitch shows up in the back wall height.

The overall height barely moves: 115-7/8 inches at 2/12, 116-1/2 at 3/12 and 117-1/8 at 4/12 on both sheds, because the roof slopes down from the front wall. The designer warns when the back wall drops under 72 inches, and it flags the 10x8 at 4/12 for exactly that: a back wall of 5 ft 6-5/16 inches is low for standing room. For the full lean-to build, see the lean-to shed guide.

What the chart tells you

Three things stand out. First, pitch changes the height of a gable shed much more than that of a lean-to: from 4/12 to 6/12 the 8x10 gains 7-13/16 inches, while the lean-tos gain 1-1/4 inches from 2/12 to 4/12, because their front wall stays at full height and the roof falls away from it. Second, a steeper pitch costs a few extra inches of rafter, not a new lumber size. Third, for a 4x8 footprint (the designer’s 8x4 lean-to) the back wall at 2/12, 3/12 and 4/12 is 89-11/16, 86 and 82-5/16 inches, so the pitch hardly matters for headroom at that depth.

Minimum pitch by roof covering

The roof covering sets the lowest pitch you can build. General practice explains why: water has to run off a shingle or a metal panel faster than it can creep up under a lap. The model code puts numbers on it, and the locally adopted edition and amendments decide for your address.

Read the metal column as the minimum for the panel type, not the pitch to aim for. The panel maker can ask for more, and the maker’s instructions decide. The same goes for the shingle wrapper.

Asphalt shingles: 2:12 and double underlayment

The 2021 IRC, R905.2.2, allows asphalt shingles only on roof slopes of 2:12 or greater, and R905.2.1 says they go on a solidly sheathed deck. From 2:12 up to 4:12, double underlayment is required. Table R905.1.1(2) describes it for areas where wind design is not required: a 19 inch strip along the eaves, then 36 inch sheets, each overlapping the last by 19 inches. At 4:12 or more, one layer applied shingle fashion with a 2 inch lap is enough.

That is why the designer’s lean-to at 2/12 and 3/12 adds a second layer of underlayment to the roofing list and tells you so. The designer offers nothing flatter than 2/12. The sequence of sheathing, underlayment and shingles is in the how to shingle a shed roof guide and the how to build a shed roof guide.

Metal roofing: 3:12, 1/2:12 with sealant, 1/4:12 standing seam

The 2021 IRC, R905.10, puts three numbers on lapped and seamed metal panels. Lapped, nonsoldered-seam metal roofs without applied lap sealant need 3:12. With lap sealant applied to the laps, the minimum drops to 1/2:12. Standing-seam systems need 1/4:12. Metal panels can go on solid or spaced sheathing.

The install steps are in the metal roof on a shed guide.

Ice barrier

Where the local climate table (Table R301.2) lists a history of ice forming along the eaves, the 2021 IRC, R905.1.2, asks for an ice barrier from the eaves to 24 inches inside the exterior wall line. It has an exception for detached accessory structures with no conditioned floor area, which covers a freestanding, unheated shed. A lean-to built against a house is not detached, so the exception may not apply to it. Ask your building department.

Shed roof pitch and snow

A steeper roof is not automatically a stronger roof. Snow sets the load on the rafters and the pitch changes how the load is checked. The two things to know are where the snow number comes from and what the designer does with it.

The snow load is local

The model code does not give one snow number. The 2021 IRC, R301.2, leaves the ground snow load, wind design, frost depth and flood hazards to the local jurisdiction, which sets them in Table R301.2. Ask your building department for the ground snow load at your address. Do not guess it from a neighbor’s shed.

30 psf and 50 psf in the designer

The designer takes a ground snow load from 20 to 80 psf and warns above 60. With a snow input of 30 psf and then 50 psf, it checked all 24 runs in the charts above. Every one picks 2x6 rafters at 16 inches on center. The pitch did not change the size.

Those allowed spans are for a 2x6 spruce-pine-fir No. 2 at 16 inches on center. The lean-to values at 30 psf are for 2/12 and 3/12; at 4/12 the allowed span at 30 psf is 11 ft 11-1/8 inches. Model-code span tables give similar numbers: the 2021 IRC, Tables R802.4.1(3) and (5), lists 11-11 at 30 psf and 9-9 at 50 psf for a 2x6 at 16 inches. Spans are measured along the horizontal projection of the rafter, not along the slope. The shed rafters guide has the full span table for 2x4 through 2x10.

The tightest of the 24 runs is the 10x8 lean-to at 50 psf, with 26 percent to spare. A shed made wider or deeper than this will run out of margin first. The designer picks the next size up when 2x6 fails, and the snow load and rafter spacing are inputs you can change on the designer page.

Low pitch, stiffer deflection limit

Deflection is how far a rafter sags under load. The 2021 IRC, Table R301.7, allows L/180 for rafters with a slope greater than 3:12 and no finished ceiling attached to them, and L/240 for everything else. A 2/12 or 3/12 lean-to lands in the stiffer L/240 group, and the designer applies it. That is why the 30 psf allowed span for a lean-to at 2/12 or 3/12 is 11 ft 8-7/8 inches, slightly under the 11 ft 11-1/8 inches at 4/12. On the designer’s 8x6 and 10x8 lean-tos it changes nothing about the lumber size.

Pitch and the rafter tie

On a gable roof the ties keep the walls from being pushed out. The 2021 IRC, Table R802.5.2(1), asks for more nails at the tie for a lower pitch and for more snow. The designer follows the rows of that table: on an 8x10 gable at 4/12 it lists 3 nails per tie at 30 psf and 5 at 50 psf, and at 5/12 or 6/12 it lists 3 and 4. A lower pitch means more nails at the same snow load.

Lean-to shed roof pitch

A lean-to shed roof pitch works differently because there is no ridge. The whole roof is one slope, so the rise takes the full depth of the shed. The designer offers 2/12, 3/12 and 4/12, with 3/12 as the default.

Which pitch for a lean-to

For a shingled lean-to, 4/12 is the pitch where the shingle underlayment drops to one layer. Below it, the code asks for two, and the designer adds the second to the list. For a metal lean-to, 3/12 meets the lapped-panel minimum without sealant. If you want the lowest back wall possible for a fence line or a garage wall, 2/12 gives the tallest back wall at 85-11/16 inches on an 8x6, but it also needs double underlayment under shingles and sealed laps under lapped metal.

Back wall height

The back wall height is the trade-off on a deeper lean-to. On the 10x8 the back wall goes from 81-11/16 inches at 2/12 to 66-5/16 inches at 4/12, which is below standing height and gets the designer’s warning. If you need headroom at the back, choose the lower pitch or make the shed shallower, because the roof falls over the whole depth. See the 8x6 lean-to plan for a complete cut list.

Shed roof pitch calculator

Use the calculator below to check a pitch before you build. Enter the roof type (gable or lean-to), the building width in feet, the pitch as rise per 12, and the overhang. It returns the roof angle in degrees, the total rise, the rafter line length along the slope, and which coverings that pitch allows under the 2021 IRC.

What to enter

On a gable roof the rise is measured over half the width of the shed. On a lean-to the roof falls across the depth, front to back, so that is the distance that counts. The pitch is the rise per 12 inches of run, so a roof that climbs 5 inches in a foot is 5.

What the result means

The result is arithmetic and a model-code reading. It is not a structural check, and it does not know your snow load, your local amendments or your panel maker’s minimum pitch. Use the shed designer when you want the cut list and the span check for the pitch you picked.

How to choose your shed roof pitch

Work down this list in order. The first two set your lowest pitch and the range you can draw, the third checks the snow and the last decides how high you can go.

1. Start with the covering. Shingles need 2:12 or more, with double underlayment up to 4:12. Lapped metal needs 3:12, or 1/2:12 with sealed laps. Standing seam allows 1/4:12.
2. Then the designer’s range. Gable sheds are 4/12, 5/12 or 6/12. Lean-tos are 2/12, 3/12 or 4/12. If your covering needs more than that, the designer cannot draw it.
3. Check the snow. Get the ground snow load from your building department, enter it as the designer’s snow input and read the span check.
4. Check the height limit. Cities measure it their own way. Elgin, Illinois, for one, measures shed height to the mid-point between the eaves and the ridge and caps it at 15 feet (City of Elgin, Quick Guide: Shed). Read the shed permits guide and call the building department.

The wind exception

One more detail can decide between 4/12 and 5/12. The 2021 IRC, R802.11, lets you skip a rafter uplift connector under one exception, and that exception needs a roof pitch of 5:12 or more, along with a basic wind speed of 115 mph or less, exposure category B, a span of 32 ft or less and rafters no more than 24 inches on center. The designer lists a rafter-to-plate connector at every bearing point whatever the pitch, so this exception does not change its list.

Where to go next

Plug a pitch into the shed designer and the cut list, height and span check update together. The 10x12 gable plan and the 8x10 gable plan have the full rafter lists, and the how to build a shed guide puts the roof in the order of the whole build.