Roof style describes the building geometry: gable, hip, shed, flat-looking low slope and combinations of those forms. Roof system describes the weather-resistant assembly installed over that geometry. The two decisions are connected but not interchangeable.
Gable roofs
A gable roof has two sloped planes meeting at a ridge, with triangular end walls.
Advantages
- Straightforward drainage on simple designs
- Fewer valleys than many complex roof forms
- Useful attic volume and familiar framing
- Broad compatibility with shingles, tile and qualifying metal systems
Tradeoffs
- End walls and roof edges need correct wind detailing
- Large unbroken planes can create significant runoff at eaves
- Additions can introduce awkward valleys and transitions
- Overhangs, fascia and edge attachment must match the exposure
A simple gable is often easier to inspect and reroof than a cut-up roof with the same area.
Hip roofs
A hip roof slopes down on every side and usually has hips running from corners to a ridge or peak.
Advantages
- No full-height gable end
- Balanced appearance on many single-story Arizona homes
- Multiple eaves can distribute runoff when discharge is planned correctly
Tradeoffs
- More hip caps, cuts and accessory material
- More labor and waste than a simple gable
- Intersections between connected hip forms can create valleys
- Attic volume can be less convenient near sloped sides
The shape does not make a roof automatically windproof. Deck attachment, roof-to-wall connections, edge details and the roof covering still control performance.
Shed and mono-slope roofs
A shed roof uses one primary plane.
Advantages
- Clean modern form
- Straightforward drainage toward one edge
- Can create high interior volume on one side
- One plane can simplify solar orientation
Tradeoffs
- All runoff concentrates at one edge
- The high wall and roof-to-wall transitions need careful flashing
- A shallow design may limit roof-covering choices
- Large spans can require more structural design
The receiving gutter, scupper or grade must handle concentrated water without dumping it onto entries, walkways or neighboring walls.
Low-slope roofs
A “flat” roof must still drain. Low-slope forms typically use membrane, modified-bitumen or spray-foam/coating assemblies rather than products that depend on rapid water shedding.
Advantages
- Low profile and compatibility with many Southwestern designs
- Potentially convenient placement for some rooftop equipment
- Suitable surface for continuous membrane or foam assemblies
Tradeoffs
- Drains, scuppers and overflow paths are critical
- Ponding and low spots can expose construction defects
- Penetrations and parapet flashings require routine attention
- Roof access does not make the surface a deck unless it was designed for that use
Complex combinations
Dormers, intersecting gables, turrets and multiple additions can add character and interior space. Every intersection also adds flashing, valley, drainage and maintenance work. Complexity should earn its keep.
When remodeling, avoid creating a short dead valley, drainage path against a wall or low-slope transition with a steep-slope material forced over it.
The roof covering must match the slope
IRC Chapter 9 separates requirements by roof-covering type. Asphalt shingles, tile, metal panels, modified bitumen and other systems have different slope, deck, underlayment and flashing rules.
Use the locally adopted code, current manufacturer instructions and project-specific approvals. A material that is durable on one geometry may be inappropriate on another.
Energy performance comes from the assembly
Shape affects attic volume, solar exposure and ventilation opportunities, but energy performance also depends on insulation, air sealing, roof color and the location of ducts and equipment. The DOE cool-roof guide explains that reflective options exist for low- and steep-slope systems and that results depend on climate and building characteristics.
A “cool” surface and a well-designed attic are complementary decisions, not competing slogans.
Questions to resolve before changing roof style
- Is the existing structure able to support the new geometry and covering?
- Where will ordinary and emergency drainage discharge?
- Which roof systems are approved at each slope?
- How will valleys, parapets, walls and penetrations be flashed?
- Does the design preserve ventilation or use a deliberate unvented assembly?
- How will solar, HVAC and future maintenance access work?
- What additional waste and labor come from the geometry?
The NRCA guidance library is organized by roofing detail and system because performance comes from the complete assembly. America Roofing can compare those conditions through an Arizona new-roofing consultation and price the actual geometry instead of recommending a shape in isolation.
Primary references
Sources used for this guide
- 2021 International Residential Code — Roof Assemblies International Code Council
- Roofing Guidelines National Roofing Contractors Association
- Consumer Guide to Cool Roofs U.S. Department of Energy