Shed and skillion roofs
A single plane sloping one way, with no ridge. Common on additions, porches, dormers and modern infill homes.
- Typical pitch
- 3:12 to 15:12, wide range
- How often we see it
- Occasional
Pitch ranges are trade convention, not code. Code sets minimum slope by material, not by roof shape.
Is this your roof?
- One plane, one direction, no ridge anywhere.
- A tall wall at the high end and a low eave at the other.
- Often attached to a larger structure rather than standing alone.
In Johnson County
Shed roofs on additions are where we find the most pitch-related code problems in Johnson County. The addition gets built to fit under an existing eave, which forces the pitch shallow, and then it gets shingled anyway. Under the 2018 IRC, section R905.2.2, asphalt shingles require at least 2:12. From 2:12 up to 4:12 the code additionally requires the low-slope double underlayment application. A shingled shed addition at 1.5:12 is not a maintenance issue. It is a roof that was never going to work.
What you can put on it
Slope decides this before preference does. Set yours and see what the code allows, then check the notes for this shape.
6:12about 27° from horizontal
ConventionalEvery common material is in play
Shingles, metal, tile or shake, each still subject to its own manufacturer minimum. Walkable for a roofer, standard labor rate, and where most Kansas City homes sit. This range is trade convention rather than a code band.
Trade convention, not code
At this slope
- Asphalt shingles
- Standing seam metal
- TPO / EPDM membrane
- Modified bitumen
- Wood shake
- Tile
Membrane drops out at 4:12 and above because nobody specifies it there, not because the code forbids it. Shake and tile carry manufacturer minimums of their own, so treat these as a starting point rather than an approval.
Asphalt shingles
WorkableOnly if the pitch supports it. Many shed roofs on additions are built shallow, which puts them in low-slope or membrane territory.
Standing seam metal
Works wellThe natural fit. One uninterrupted run from high wall to eave, with no penetrations if it is detailed well.
Membrane
Works wellThe correct answer below 2:12, and common on flat-roofed modern additions.
What we check first
The failure points specific to this shape, marked on the roof and listed in the order a roofer looks at them.
- The high wall junction and its counter-flashing, the leak point on almost every shed roof.
- The actual measured pitch, because shed roofs are frequently shallower than they look.
- Whether the single eave and its gutter can handle the entire roof's water, since all of it goes to one side.
- Ventilation, which is awkward with no ridge to vent through.
What moves the price
Square footage is a poor predictor on its own. These are the things that actually change the number on this shape.
- The simplest possible shape to cover, so material waste is minimal.
- The high wall junction is the expensive detail, because counter-flashing into the wall properly is skilled work.
- Pitch determines the whole specification. A shallow shed roof needs membrane or metal, which changes the price bracket entirely.
- Usually small in area, so mobilization is a large share of the total.
Common questions
What is the minimum pitch for a shed roof with shingles?
Two in twelve. Under the 2018 IRC, section R905.2.2, asphalt shingles may only be used at 2:12 and above. From 2:12 up to 4:12 the code additionally requires the low-slope double underlayment application rather than a standard single layer. Below 2:12 the roof needs a membrane such as TPO, EPDM or modified bitumen, or a suitable metal system.
Why does my addition's shed roof leak where it meets the house?
That junction is the hardest part of a shed roof and the most commonly botched. Done properly, the roofing turns up the wall and separate counter-flashing is let into or behind the cladding above it. Done cheaply, someone runs a bead of sealant along the top of the shingles against the siding, which lasts a couple of seasons at most.
How do you ventilate a shed roof?
It takes more planning than a ridged roof because there is no ridge to exhaust through. The usual approaches are intake at the low eave with exhaust vents set high on the plane near the tall wall, or a vented assembly built into the roof structure itself. Over conditioned space it is often simpler to build it as an unvented assembly with the insulation detailed accordingly.
More answers on the roofing questions page, or see every roof shape side by side.
Often confused with
Flat and low slope
Anything under 2:12. Not actually flat, since a working low slope roof always has some fall built in, and it needs a membrane rather than shingles.
Butterfly
Two planes sloping inward to a central valley, like an open book. A mid-century modern signature, and entirely dependent on that central channel working.
Cross gable and combination
Two or more gable sections meeting at right angles, creating valleys where the planes intersect. A shape we see constantly on larger Johnson County homes.
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