How a gable roof is built

What this roof builds

A gable roof over a 12 × 12 ft building: 6-in-12 pitch, rafters 24 in on center, asphalt shingles. Every part is below, in the order the steps use it. Nails and metal connectors are not listed.

≈2–3 days for a small crew

This guide shows the sequence, not a design. Lumber sizes, spacing and connections come from your plans and local code — check them before cutting anything.

Set the ceiling joists

Ceiling joists run wall to wall across the top plates, one at every rafter position. They carry the ceiling and tie the two walls together, so the rafters can’t push them apart.

• Lay out 24 in on center on both top plates, starting at one gable end.
• Toe-nail each joist to the plates. It gets nailed to its rafter in step 3.

≈2 hr · 7 joists · 24 in on center

Parts: 7 × Ceiling joist / rafter tie, 2×6 × 14 ft

With a ridge board — not a structural ridge beam — these ties are what keep the walls from spreading. Don’t skip or cut them.

Set the ridge board

The ridge board runs the full length of the roof at the peak. It gets braced level and plumb until the rafters lock it in place.

• Brace it level along its length, at the height your rafter layout gives.

≈1 hr · 3 ft rise over a 6 ft run = 6-in-12 pitch

Parts: 1 × Ridge board, 2×8 × 14 ft

The 3 ft rise is measured on the rafter layout line, so the ridge itself sits a little higher than 3 ft above the plates. Sight down the board and set any crown (bow) facing up.

Add the common rafters

Rafter pairs run from the top plates up to the ridge, one pair at every ceiling joist: seven pairs at 24 in on center, including one at each gable end.

• Nail each pair to the ridge, working from one end.
• Nail each heel to the top plate and to its ceiling joist.

≈4 hr · 7 pairs · 24 in on center

Parts: 14 × Rafter, 2×6 × 8 ft

Set opposite rafters together so the ridge stays centered. Add metal rafter-to-plate ties where the plans call for them. (Most real roofs also run the rafter tails 12–24 in past the wall for an overhang; this model leaves that off.)

Sheathe both slopes

Sheets go on with the long edge running across the rafters. The second row is offset 4 ft so the end joints don’t line up, and every end joint lands on a rafter.

• Start at the eave with a full 8 ft sheet.
• Offset the next row by 4 ft so the joints break.

≈3 hr · 6 sheets, 4 × 8 ft · 2 rows per side

Parts: 6 × Roof sheathing, 4×8 ft sheet

Leave a 1/8 in gap at every sheet edge so the panels can expand. With rafters 24 in apart, most panels also need metal edge clips (H-clips) between rafters; the panel’s span rating tells you.

Drip edge at the eaves

Metal drip edge goes along both eaves first, directly on the sheathing, so water running off the roof drips clear of the wall.

• Fasten it tight to the eave edge, lapping pieces 2 in.

≈30 min · 2 eaves · 12 ft each

Parts: 3 × Drip edge, 10 ft piece

At the eaves the drip edge goes under the underlayment. At the rakes it goes over. The order matters.

Underlayment, then the rakes

Synthetic underlayment rolls out in horizontal courses, starting at the eave and lapping each course over the one below. Then drip edge goes up both rakes, over the underlayment.

• Run the first course along the eave, over the drip edge.
• Lap the next course over it, then fasten drip edge up the rakes.

≈1.5 hr · 2 courses per side · 1 roll

Parts: 1 × Synthetic underlayment, roll; 4 × Drip edge, 10 ft piece

Lap widths and fastener spacing vary by product; follow the instructions printed on the roll. The top course usually runs over the ridge onto the other slope.

Starter strip, then shingles

A starter strip goes along the eave first. Then the shingle courses work up the slope, each covering most of the one below and leaving about 5⅝ in exposed.

• Set the starter strip so it hangs just past the drip edge, about 1/4–3/4 in.
• Snap chalk lines and work up toward the ridge, staggering the joints.

≈1 day · ≈14 courses per side · 5⅝ in exposure

Parts: 1 × Starter strip, bundle; 6 × Architectural shingles, bundle

Exposure, overhang and nail placement come from the shingle wrapper. Follow it exactly, or the manufacturer’s warranty may not apply.

Cap the ridge

Hip-and-ridge cap shingles fold over the peak and seal the top courses. Start at the end opposite the prevailing wind so each lap points downwind.

• Fold each cap over the ridge and nail it at the exposure printed on the bundle.

≈1 hr · One bundle covers the 12 ft ridge

Parts: 1 × Hip & ridge cap, bundle

If the plans call for a ridge vent, it goes on before the cap.

Done

That’s the roof, start to finish. Check it from the ground: a straight ridge, even courses, and drip edge tight along every edge.