Roof Dormers Guide | Types, Design & Installation

Dormers add headroom, light and ventilation while enhancing architectural character. Success depends on proportion, structural integration and meticulous waterproofing.

Types of Dormers

Gable (dog-house)
Shed
Hip
Eyebrow
Wall and Link dormers
Recessed dormers

Design Considerations

Proportion to main roof and façade
Window sizing and placement
Integration with roofline and style

Structure and Compliance

Framing modifications require engineering for load paths. Comply with NCC, energy requirements and, where relevant, heritage controls. Plan approvals may be required.

Waterproofing and Flashing

Critical flashings include valleys, sidewalls and head flashings. Use compatible metals, adequate upstands and membrane reinforcement at junctions.

Detail Diagram (described)

1) Step flashing at sidewalls; 2) Valley flashing with underlap; 3) Head flashing under cladding; 4) Sarking continuity and counter-flashing.

Costs

Small gable dormer: $9,000–$18,000
Large shed dormer: $25,000–$65,000 depending on finishes
Design/engineering: $2,000–$7,000
Permits and approvals: council dependent

Adding Dormers to Existing Roofs

Assess structure, services and egress requirements. Expect construction disruption and temporary weather protection strategies.

Maintenance and Issues

Leaks at flashing interfaces
Condensation in unvented cavities
Paint and cladding maintenance

Case Studies

Federation home, Mosman: Paired gable dormers added usable floor area and cross-ventilation, with concealed box gutter overflows for protection.

Conclusion

Well-proportioned dormers with engineered framing and robust flashing deliver lasting value. Coordinate architecture, structure and waterproofing from concept through build.