How do you build a soffit under a roof overhang?
Short answer. To build an exterior soffit, you frame a level nailing surface under the rafter tails, usually with lookouts running from the fascia back to a ledger on the wall, then install trim channels, soffit panels or boards, and vents so attic intake air can still flow. An interior kitchen or ceiling soffit is a different project, framed and finished with drywall.
Two common soffit styles
- Level (boxed) soffit: a flat ceiling under the overhang, built with horizontal lookouts. This is the standard look on most Georgia homes.
- Sloped soffit: panels attached directly to the underside of the rafter tails, following the roof pitch. Simpler, with no lookouts.
Building a level soffit
- Check the fascia. It must be straight and sound. Replace rotted fascia or sub fascia first.
- Install a ledger. Snap a level line on the wall from the bottom of the fascia, and fasten a ledger board into the wall framing along that line.
- Add lookouts. Run short horizontal framing members from the ledger to each rafter tail, commonly at the rafter spacing.
- Install channels. For vinyl or aluminum, fasten J-channel or F-channel along the wall and at the fascia to receive the panels.
- Cut and install panels. Cut panels slightly shorter than the opening so they can expand, slide them into the channels, and nail through the center of the nailing slots without driving tight.
- Wrap the fascia. Cover the fascia with aluminum coil or a fascia cap that laps over the soffit edge.
Keep the attic breathing
Use vented panels or install vent strips where the attic needs intake, and make sure nothing blocks the path above the wall top plate. Install baffles in the rafter bays so insulation cannot fill the gap. A beautiful soffit that seals off the attic causes heat and moisture problems under the roof.
Materials
Vinyl and aluminum are the easiest for most homes. Wood and fiber cement work well but need priming and paint. Use corrosion resistant fasteners and keep the work level for a clean look. See roof anatomy explained and roof ventilation basics.