A gable roof is built by framing two sloped sides that meet at a peak, then sheathing and covering them with roofing material

A gable roof has two rectangular planes that slope down from a central ridge, forming a triangular wall (the gable) at each end. Building one involves three main stages: framing the roof structure with rafters or trusses, covering the frame with plywood or OSB sheathing, and installing underlayment and shingles or other roofing material. The process takes several weeks and requires working at height, so most homeowners hire a roofing contractor rather than doing it themselves.

The framing stage is the foundation for everything that follows. If the frame is not square, level, and properly supported, the roof will leak, sag, or fail prematurely. Sheathing protects the frame from weather while the work is in progress. The final covering—shingles, metal, or tile—is what actually sheds water and determines how long the roof lasts.

Key Takeaways

  • Gable roof framing uses either individual rafters cut and installed one at a time, or prefabricated trusses that arrive ready to set in place.
  • The frame must be tied into the walls below with a rim board or top plate, and the peak must be braced with collar ties or a ridge beam to prevent spreading.
  • Sheathing is nailed to the rafters in a staggered pattern, with gaps left at the edges to allow for expansion and contraction.
  • Underlayment, drip edge, and flashing go down before shingles to direct water toward the gutters and prevent leaks at valleys and penetrations.

Framing the roof structure with rafters or trusses

The two main methods are stick framing (cutting and installing individual rafters on site) and truss framing (using prefabricated triangular units). Trusses are faster and more common in new construction because they arrive from the factory already cut and braced. Stick framing gives you more flexibility if the roof has unusual angles or if you need to create attic space with a specific shape.

With stick framing, rafters are typically 2×6 or 2×8 lumber, spaced 16 or 24 inches apart. Each rafter is cut with a bird's mouth notch where it sits on the top plate of the wall, and the top ends are cut at an angle to meet at the ridge. The slope (or pitch) of the roof determines these angles. A 6:12 pitch, for example, means the roof rises 6 inches for every 12 inches of horizontal run. Steeper pitches shed water faster but require more material and are harder to work on.

Once rafters are in place, they must be braced to prevent the peak from spreading outward under the weight of snow or wind. Collar ties (horizontal boards connecting opposite rafters near the peak) or a ridge beam (a structural beam running the length of the peak) do this job. Without bracing, the roof will gradually push the walls apart and the peak will sag.

Trusses come pre-assembled and pre-braced, so installation is mainly a matter of setting them on the walls, spacing them correctly, and nailing them down. This is faster but leaves no usable attic space unless you use special scissor trusses that have a sloped ceiling inside.

Installing sheathing over the frame

Once the frame is complete and braced, sheathing—usually 1/2-inch plywood or OSB (oriented strand board)—is nailed to the rafters. Sheathing serves two purposes: it braces the rafters against racking (twisting), and it provides a nailing base for the roofing material. It also protects the frame from weather while work is in progress.

Sheathing is installed in horizontal rows, starting at the eaves and working toward the peak. Sheets are staggered so that joints do not line up from row to row. Nails are spaced 6 inches apart along the edges and 12 inches apart in the field (the middle of the sheet). A 1/8-inch gap is left between sheets to allow for expansion and contraction as humidity changes; without this gap, the sheathing will buckle.

At the edges of the roof, sheathing typically overhangs the wall by 1 to 2 feet to form an eave. This overhang protects the wall from rain and sun. The overhang is supported by lookouts (short beams that extend from the wall) or by extending the rafters themselves beyond the wall line.

Adding underlayment and drip edge

Underlayment is a water-resistant layer that goes down on top of the sheathing, before shingles. It catches water that gets under the shingles and directs it toward the gutters. Most underlayment today is synthetic (plastic-based) rather than felt, because it lasts longer and does not deteriorate in heat. Underlayment is rolled out horizontally, starting at the eaves, with each row overlapping the one below by at least 4 inches.

Drip edge is a metal strip that runs along the eaves and gables, tucked under the underlayment at the eaves and over it at the gables. Drip edge prevents water from running back under the sheathing and into the walls. At the eaves, water drips off the edge and into the gutter. At the gables, water runs down the face of the drip edge and away from the wall.

Valleys (the places where two roof planes meet) and penetrations (where pipes, vents, or chimneys come through the roof) need special flashing—metal or rubber pieces that overlap the underlayment and direct water away. Flashing is installed before shingles and is a common source of leaks if it is not done correctly.

Installing shingles or other roofing material

Shingles are the most common roofing material. Asphalt shingles come in bundles and are nailed to the sheathing in overlapping rows, starting at the eaves. Each shingle overlaps the one below it, so water runs down the face of the roof without getting under the shingles. Nails are driven through the shingles into the sheathing, and the nails are covered by the shingles in the row above.

The first row of shingles at the eaves is usually a starter strip—a full-width shingle with adhesive on the back, or a row of shingles installed upside down. This starter strip ensures that water does not run under the first course of shingles. Subsequent rows are offset so that the joints do not line up, which would create a path for water to follow.

Other roofing materials—metal panels, wood shakes, slate, or tile—follow similar principles but have different installation details. Metal roofing is fastened with screws rather than nails and requires special flashing at seams. Wood shakes are nailed individually and left with gaps to allow for expansion. Slate and tile are heavy and require a stronger frame, and they are set in mortar or fastened with hooks.

Ventilation and soffit details

A gable roof needs ventilation to prevent moisture from building up in the attic. Soffit vents (openings in the eave) allow air to flow into the attic, and ridge vents or gable vents allow air to flow out. Without ventilation, moisture condenses on the underside of the roof sheathing, leading to rot and mold.

The soffit (the underside of the eave) is usually covered with plywood or vinyl panels, with vents cut into it. The soffit is fastened to the lookouts or rafter tails and provides a finished appearance. Gutters are hung from the edge of the soffit or from the fascia board (the board that runs along the edge of the roof).

Common mistakes and how to avoid them

The most common mistake is inadequate bracing at the peak. Rafters that are not tied together with collar ties or a ridge beam will gradually spread, causing the peak to sag and the walls to crack. This is not always visible from inside the house, but it happens over time and is expensive to fix.

Another common mistake is poor flashing at valleys and penetrations. Water finds its way to the lowest point, and if flashing does not overlap correctly or is not sealed properly, water will leak into the attic. Flashing should overlap the underlayment by at least 4 inches and should be sealed with roofing cement or caulk.

Inadequate ventilation is also common, especially in older houses where soffit vents are blocked by insulation or debris. Without ventilation, the roof deck stays damp, shingles deteriorate faster, and ice dams form in winter. If you are adding insulation to an attic, make sure you leave a 1-inch air gap between the insulation and the roof sheathing.

When to hire a contractor versus doing it yourself

Gable roof framing and installation require working at height, using power tools, and understanding structural principles. A mistake in framing can compromise the entire structure. A mistake in flashing or sheathing can lead to leaks that are hard to find and expensive to fix. Most homeowners should hire a licensed roofing contractor.

If you have experience with carpentry and are comfortable working on a ladder or scaffolding, you might frame a roof yourself. However, sheathing and roofing material installation are best left to professionals who have the right tools, safety equipment, and experience with the details that prevent leaks. A roofing contractor can also spot problems with the existing structure—rot, inadequate bracing, or poor ventilation—that you might miss.

Frequently Asked Questions

What is the difference between a rafter and a truss?

A rafter is a single board that slopes from the wall to the peak. A truss is a prefabricated triangular frame made of several boards connected with metal plates. Trusses are faster to install and come ready to use. Rafters are cut on site and give you more flexibility in design.

How much overhang should a gable roof have?

Most gable roofs have an eave overhang of 12 to 24 inches. The overhang protects the wall from rain and sun. A longer overhang provides more protection but requires longer rafters and more material. Local building codes may specify a minimum overhang.

Do I need a ridge vent if I have gable vents?

Gable vents alone are not as effective as a ridge vent with soffit vents. Gable vents work best when there is a breeze, but on still days, air does not circulate. A ridge vent with soffit vents creates a continuous flow of air from the eaves to the peak, which works regardless of wind direction.

What pitch should my gable roof be?

Pitch depends on your climate and the roofing material. In areas with heavy snow, a steeper pitch (8:12 or higher) sheds snow better. In dry climates, a lower pitch (4:12 or lower) is common. Asphalt shingles work on pitches as low as 3:12, but metal and tile may have different minimums. Check the manufacturer's specifications and local building codes.

How long does a gable roof last?

Asphalt shingles typically last 15 to 25 years, depending on climate and maintenance. Metal roofing lasts 40 to 70 years. Wood shakes last 20 to 40 years. Slate and tile can last 50 to 100 years or more. Regular maintenance—cleaning gutters, removing debris, and fixing leaks promptly—extends the life of any roof.