What is the difference between roof decking and roof sheathing?
On a typical house
Panels or boards nailed over rafters or trusses form a flat surface for the roof. Codes call it sheathing, roofers call it decking, and the work is the same either way.
Where the terms mean different things
- Exposed tongue-and-groove decking. Many North Georgia mountain homes and cabins have beam ceilings with thick wood planks that are both the finished ceiling inside and the roof deck outside. There is no attic.
- Structural steel deck. On commercial buildings, the roof deck is corrugated steel spanning between joists, with insulation and a membrane on top.
- Sheathing over a deck. In some systems, rigid insulation goes on top of a structural deck, and a second layer of panels, often called a nail base, goes over the insulation for the shingles.
Why this matters for roofing
With an exposed plank ceiling, there is no attic for ventilation or insulation. Insulation goes on top of the deck, nails must not poke through the finished wood below, and moisture control works differently. Reroofing these homes takes more planning than a standard tear-off, and the scope should spell out insulation, nail base panels and fastener lengths.
Ventilation differences
A conventional house vents the attic. A home with a deck that is also the ceiling may use a vented space above the insulation or an unvented assembly designed to control condensation. Read roof ventilation basics, and for panel choices on standard roofs, OSB vs plywood roof decking.