Roof Style
What Is a Bonnet Roof? Structure, Design, and Performance
Also called: Kicked eaves roof, bonneted roof, reverse mansard roof, canopy roof
Bonnet roof is a dual-pitched roof design featuring two slopes on each side, with the lower slope set at a gentler angle and extending outward beyond the walls to form overhanging eaves.
In plain English
A bonnet roof is a roof type characterized by two slopes on each side, with the lower slope set at a gentler angle than the upper slope, creating an overhanging eave that typically extends beyond the building’s exterior walls.
How bonnet roof works
Bonnet roof refers to a distinctive roof structure characterized by two slopes on each of its four sides, where the lower slope is steeper and extends beyond the exterior walls to form wide eaves or overhangs. The upper portion of the roof resembles a standard hip roof with a moderate pitch, while the lower, more pronounced slopes create a flared appearance at the eaves. This geometry results in a roof with a continuous ridge at the top and a break in pitch partway down each slope, enhancing both the visual profile and functional performance.
The design of a bonnet roof offers several technical advantages. The extended lower slopes and generous eaves provide effective water drainage away from the building’s foundation, reducing the risk of water infiltration and soil erosion. The dual-pitch configuration also promotes efficient snow shedding and can improve wind resistance by reducing uplift forces at the roof edges. Structurally, the bonnet roof allows for increased usable space beneath the eaves, often accommodating covered porches or verandas, and can enhance attic ventilation due to the variation in roof pitch.
Bonnet roofs are commonly used in regions with heavy rainfall or intense sun exposure, where the extended eaves protect walls and windows from the elements. They are frequently found in residential architecture, particularly in traditional and colonial styles, where both functional and aesthetic considerations are important.
Why it matters for your roof
The bonnet roof is often used in hot and humid climates to provide additional protection from the sun and rain. It also affects how homeowners, contractors, and specifiers evaluate roof durability, cost, risk, and long-term value.
Benefits
ENHANCED EAVE PROTECTION
The extended lower slopes of a bonnet roof provide additional coverage for walls and porches, improving water runoff management.
IMPROVED ATTIC VENTILATION
Distinct roof planes and overhanging eaves create opportunities for effective attic ventilation, reducing heat buildup and moisture accumulation.
INCREASED USABLE SPACE
The unique geometry of a bonnet roof allows for expanded upper-level living or storage space beneath the steeper upper slope.
SUPERIOR RAIN DRAINAGE
Dual-pitched slopes efficiently channel rainwater away from the structure, minimizing the risk of water infiltration at the eaves.
Limitations
COMPLEX FRAMING REQUIREMENTS
Bonnet roofs demand intricate framing due to their dual-pitch geometry, increasing structural complexity and construction precision needs.
EAVES WATER MANAGEMENT
The extended lower slope creates large eaves that complicate gutter placement and increase risk of water pooling or overflow.
WIND UPLIFT VULNERABILITY
The pronounced overhangs of bonnet roofs are more susceptible to wind uplift forces, especially in hurricane-prone regions.
ATTIC VENTILATION CHALLENGES
The unique roof shape can restrict airflow in attic spaces, complicating effective ventilation and moisture control strategies.
Common problems
POOR DRAINAGE AT LOWER SLOPES
Bonnet roof geometry often causes water to pool at the lower slopes, increasing leak and moisture intrusion risks.
WIND UPLIFT AT EAVES
The extended eaves of a bonnet roof are highly susceptible to wind uplift, leading to potential structural damage or roof detachment.
SNOW ACCUMULATION ON FLARED SECTIONS
Flared lower sections of bonnet roofs can trap snow, resulting in excessive snow load and possible structural stress or collapse.
COMPLEX LOAD DISTRIBUTION
The dual-pitch design of bonnet roofs creates uneven load distribution, increasing the risk of localized structural failure under heavy weather conditions.
Where you'll see it
TROPICAL CLIMATE PROTECTION
Bonnet roofs are ideal for tropical regions where extended eaves provide shade and direct rainwater away from building walls.
COLONIAL ARCHITECTURE MATCH
Bonnet roofs are commonly used to replicate French Colonial or Creole architectural styles that require distinctive flared eaves.
VERANDAH INTEGRATION
Bonnet roofs are selected when a continuous covered porch or verandah is needed around the perimeter of a home.
LOFT SPACE CREATION
Bonnet roofs are chosen to maximize usable attic or loft space due to their dual-pitched design and steep upper slope.
Don't confuse it with
Not to be confused with roof pitch, attic framing, or other roof style names that describe different geometry.
- bonnet roof vs mansard roof
- bonnet roof vs hip roof
- bonnet roof vs gambrel roof
- bonnet roof vs pyramid roof
Regional & climate notes
Most relevant in: Rain-heavy climates, Snow-heavy climates, High-wind climates.
Frequently Asked Questions
What is a bonnet roof and how is it defined in roofing terminology?
A bonnet roof is a type of roof with two slopes on each side, where the lower slope is steeper and extends beyond the walls, creating overhanging eaves for added protection and shade.
How does a bonnet roof help with water drainage and protection of exterior walls?
A bonnet roof features double slopes on each side, with the lower slope extending outward. This design efficiently channels water away from the structure and provides extra protection for exterior walls and foundations.
Why is a bonnet roof considered important for protecting exterior walls and providing additional shade?
A bonnet roof is important because its extended lower slopes protect exterior walls from rain and sun, reducing weathering and providing additional shade, which helps improve energy efficiency and comfort for the building.
How does a bonnet roof affect a building’s energy efficiency and weather resistance?
A bonnet roof improves weather resistance by directing water away from walls and provides shade, reducing solar heat gain. Its overhanging eaves can enhance energy efficiency, but proper insulation and ventilation are essential for optimal performance.
How do you measure the slope and overhang of a bonnet roof for accurate evaluation?
Measure the slope of a bonnet roof using a digital level or inclinometer on the main and lower slopes. Measure the overhang from the exterior wall to the edge of the lower eave horizontally.
What factors should be considered when deciding if a bonnet roof is suitable for your climate and building design?
Consider local rainfall, snow loads, wind exposure, attic ventilation needs, and desired overhang for shade or porch coverage when evaluating if a bonnet roof suits your climate and building design.
Related terms
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