Frame Dormer Structure
Building the walls, rafters, and ridge that form your new dormer. Proper framing creates a solid structure that ties seamlessly into your existing roof.
Why Proper Dormer Framing Matters
The dormer frame must carry roof loads while integrating with your existing structure. Poor framing leads to sagging roofs, water infiltration, and expensive repairs. Each component works together: the front wall supports the rafters, the cheek walls tie into the existing roof, and the ridge distributes loads evenly. Using proper lumber sizes, spacing, and connectors ensures your dormer will perform for decades. This isn't the place to cut corners - the dormer is exposed to the same weather loads as the rest of your roof and must meet the same structural standards.
Tools & Materials You'll Need
Step-by-Step Guide
Build Dormer Front Wall
The front wall is the face of your dormer and supports the rafter ends:
Planning Note: Build the wall on the attic floor, then raise it into position. This is safer and more accurate than trying to frame in place.
- Cut bottom and double top plates to dormer width
- Mark stud locations at 16 inches on center
- Frame window rough opening with king studs, jack studs, and header
- Assemble wall flat on attic floor, squaring corners
- Raise wall into position and brace temporarily
- Secure bottom plate to floor framing with structural screws
- Verify wall is plumb and level before permanent attachment
Frame Side Walls (Cheek Walls)
Side walls connect the front wall to the existing roof slope:
For Shed Dormers:
Cheek walls are triangular, running from the front wall corner down to meet the existing roof sheathing. Frame with studs perpendicular to roof slope.
For Gable Dormers:
Cheek walls extend from the front wall to the main roof, with a sloped top plate matching the dormer roof pitch. More complex geometry.
- Measure from front wall corner to roof intersection point
- Cut angled bottom plate to sit on existing roof sheathing
- Install studs at 16 inches on center, with angled top cuts
- Attach bottom plate to roof sheathing and rafters below
- Connect corner to front wall with overlapping plates
Install Ridge Board or Connect to House
The ridge setup depends on your dormer style:
Structural Note: Gable dormers need a ridge board at minimum, or a structural ridge beam if the roof pitch is low. Your engineer's plans will specify which is required.
Shed Dormer Ridge:
- • Install ledger board on house wall at calculated height
- • Ledger carries the top of all dormer rafters
- • Use lag screws into wall studs every 16 inches
- • Flash ledger properly to prevent water infiltration
Gable Dormer Ridge:
- • Position ridge board from front wall peak to main roof
- • Support temporarily at both ends while installing rafters
- • Ridge height determines headroom - verify measurements
- • Use ridge beam with posts if engineer specifies
Install Dormer Rafters
Rafters form the dormer roof structure and must be cut precisely:
Rafter Cut Angles:
- Plumb Cut: Vertical cut at ridge (angle matches roof pitch)
- Seat Cut: Horizontal and vertical notch where rafter sits on wall
- Tail Cut: End cut for overhang (plumb or square)
- Calculate rafter length using roof pitch and span
- Mark and cut one test rafter, verify fit
- Use test rafter as pattern for remaining rafters
- Install rafters at 16 inches on center, starting from one end
- Toenail to top plate and face-nail to ridge board
- Check each rafter for plumb before securing
Pro Tip: Use a speed square with the roof pitch marked to make consistent cuts. Most speed squares have common pitch angles printed on them.
Add Blocking and Connectors
Blocking and metal connectors complete the structural frame:
- Install blocking between rafters at the wall line (provides nailing for soffits)
- Add blocking at ridge if needed for ventilation baffles
- Install hurricane ties connecting each rafter to the top plate
- Add rafter ties at ridge for gable dormers if specified
- Install any specified hold-down hardware at corners
- Check all connections before proceeding to sheathing
Inspection Ready: Before sheathing, the framing should be complete and ready for inspection. Take photos of all connections and blocking for your records.
Pro Tips
- ✓Pre-cut all rafters on the ground before going up - safer and more accurate
- ✓Crown all rafters before installing - install crown side up for consistency
- ✓Use temporary bracing to hold rafters plumb while nailing - remove after sheathing
- ✓Mark rafter locations on both ridge and wall plate before starting installation
- ✓Keep construction adhesive handy for extra bond at critical connections
Frequently Asked Questions
What is the difference between a shed dormer and a gable dormer frame?▼
A shed dormer has a single sloped roof that extends from the main roof, creating maximum interior space. Framing is simpler with rafters running one direction. A gable dormer has a peaked roof with its own ridge board, matching the house's gable ends. It's more complex to frame but adds architectural character. Shed dormers are practical for maximizing space; gable dormers better maintain traditional aesthetics.
What lumber size should I use for dormer rafters?▼
Dormer rafter size depends on span and local snow/wind loads. For spans under 10 feet, 2x6 rafters at 16 inches on center are common. Longer spans may require 2x8 or 2x10 rafters. Your structural engineer will specify the exact requirements. Always match or exceed the lumber grade and size called for in the plans. Using undersized rafters can lead to sagging and structural failure.
How do I ensure the dormer is square and level?▼
Start by ensuring the existing roof opening headers are level. Use a string line from corner to corner (diagonals should be equal for square). Check the front wall for plumb at multiple points. Use a long level on the top plate. For the ridge, use a level and also measure down from both ends to the floor - they should be equal. Make adjustments before nailing anything permanently.
Do dormer rafters need hurricane ties or other connectors?▼
Yes, modern building codes require metal connectors at key framing points. Hurricane ties connect rafters to the top plate. Joist hangers support header connections. Rafter ties may be required at the ridge. These connectors are inexpensive insurance against high winds and are typically required for inspection approval. Your engineer's plans should specify connector types and locations.