What Is a Skillion Roof?
A skillion roof has one flat surface that slopes in one direction. Builders also call it a shed roof or mono-pitch roof. It can cover a small building, an addition, or part of a larger home.
Comparing shapes? See our roof-style comparison guide for pictures, tradeoffs, and planning questions.
Skillion vs. Gable Roofs
| Question | Skillion | Gable |
|---|---|---|
| How many main slopes? | One surface slopes in one direction. | Two slopes meet at the top. |
| Where does rain go? | Toward the low roof edge. | Toward roof edges on both sides. |
| What should the designer check? | The high wall, low-side headroom, and drains. | The top ridge, gable ends, and attic layout. |
Ask a qualified designer to compare the plans for your home. Our gable roof guide and roof-style guide can help you prepare questions.
How Skillion Roofs Are Built
Builders may use roof beams, rafters, or trusses. Trusses are roof frames that often arrive ready to install. The choice depends on the span, wall heights, materials, and local loads. A simple shape still needs a sound design.
The frame must carry the roof’s weight and loads from wind, rain, snow, and earthquakes. The International Residential Code sets rules for roof loads. Designers must use the roof live load or ground snow load, whichever controls the design. Local rules and site conditions may add requirements.
Use approved plans and a qualified contractor. This overview does not explain how to build the frame.
Roof Slope and Rain Drainage
A skillion roof has no single standard slope. Your chosen covering sets the minimum slope and rules for the layer beneath it. For example, the 2024 IRC allows asphalt shingles at 2:12 or steeper. A 2:12 slope rises two inches for each 12 inches across. Slopes from 2:12 to less than 4:12 need double underlayment, the layer beneath the shingles.
Rain runs toward one low edge. Ask the designer to size gutters and drains for that flow. In snowy areas, the design must also account for snow buildup and sliding snow. It must protect people and property below the edge.
Advantages of a Skillion Roof
- Simple shape: One slope may need fewer ridges, valleys, and sealed joints than a roof with several sections.
- More height on one side: The high wall can make room for upper windows or a tall ceiling. Plan headroom at the low side, too.
- One drainage direction: You can direct rain toward one edge. The drains and site must handle that water.
- Room for solar: One open surface can hold panels if its direction, shade, slope, and strength suit the project.
Tradeoffs
- Lower headroom: Rooms can lose height near the low wall.
- Water and snow: One edge receives water from the whole slope. Plan for snow there, too.
- High wall: The taller wall and roof edges need support and weather seals suited to the site.
- Wind: Wind pushes and pulls on this shape in different ways from a gable or hip roof. A designer must plan how those forces pass through the building.
FEMA guidance explains that wind forces change with roof slope and building shape. A skillion roof can work in a windy area when a designer plans its supports and fasteners for the site.
How Long Does a Skillion Roof Last?
Roof shape alone does not set its life. Materials, slope, drainage, vents, and the quality of the work all matter. Weather and upkeep matter, too. Insulation reduces heat flow but does not replace roof checks and repairs.
Solar Panels on a Skillion Roof
A single slope may offer useful space for solar panels. The U.S. Department of Energy says panels tend to work best on unshaded, south-facing roofs. It gives a slope range of 15 to 40 degrees, while noting that other roofs can work.
Ask a solar installer to check shade, roof age, and usable space. They should also check the roof’s strength and how the panels attach. Plan access for later roof repairs.
Variations
A split mono-pitch roof has single-slope sections at different heights. A butterfly roof has two slopes that meet in a low central valley. It needs different drainage details. Designers may also combine skillion and gable roofs on one home.
A curved roof uses an arc instead of a straight slope. Repeated sloping sections can form a sawtooth roof. Each shape needs its own design and roof details.
Skillion Roof Cost
A small shed roof and a full house roof are different jobs. Size, wall height, slope, and materials affect the price. So do changes to the frame, removal work, permits, and local labor costs.
Ask roofers to price the same plans and materials. Have them list the frame, roof base, covering, insulation, drains, and removal work. Check permits and warranty terms, too. Our cost guide includes a checklist for comparing bids.