What is a pitched roof build up, and how is a pitched roof built?
Short answer. A pitched roof build up is the stack of layers from the framing out: rafters or trusses, the roof deck, underlayment, the roof covering, and ventilation and flashing details. Building one means framing to an engineered or code based design, sheathing it, then weatherproofing it layer by layer from the eaves up.
Typical US build up (inside to outside)
- Ceiling and insulation on the attic floor, or between rafters in a vaulted ceiling with a vent channel above.
- Framing: engineered trusses or site built rafters with ridge board, collar ties or rafter ties.
- Roof deck: OSB or plywood sheathing.
- Drip edge at the eaves, then ice and water barrier at valleys and penetrations.
- Underlayment: synthetic or felt over the whole deck; see synthetic underlayment vs felt.
- Starter strip and shingles, or metal panels.
- Flashing at walls, chimneys and pipes, and ridge vent and cap at the peak.
Typical UK and tile build up
Rafters, a breathable membrane, timber battens (and counter battens in some designs), then tiles or slates hung on the battens, with ridge tiles bedded or dry fixed. Same principle, different materials.
Basic steps to build one
- Design the pitch, span and loads; trusses come with engineered drawings, and stick framing follows code span tables.
- Set the framing on the wall plates with proper connectors.
- Sheathe the frame, then dry it in with underlayment the same day if possible.
- Install ventilation intake and exhaust, flashing and the roof covering.
Pitch decides which coverings are allowed: asphalt shingles need at least 2/12. A permit is required for new roof framing in Georgia jurisdictions. See roof anatomy explained and roof ventilation basics.