What Does ADU Roofing Cover, and Which Materials Are Allowed?

Key takeaways

• Roofing is the layer that sheds water. It sits on the roof frame.
• Common ADU roofs are asphalt shingle, metal, tile and low-slope membrane.
• Roof coverings are rated Class A, B or C for fire. Class A resists the most.
• In California fire hazard zones, roof assemblies must be Class A.
• Slope limits which materials work. Low-slope roofs need different products.
• Plan for solar early if the roof will carry panels.

What it means, in plain English

The roof frame is the bones. Roofing is the skin. It keeps rain, sun and embers out.

Roofing has layers. Sheathing is the board laid over the rafters. Underlayment is a water barrier on top of it. The covering is what you see: shingles, metal or tile. Flashing is metal at edges, walls and vents that stops leaks at joints.

Slope is how steep the roof is. Most shingles need a steeper roof. Near-flat roofs need a membrane made for low slopes.

Why it matters to you

A leak ruins insulation, drywall and floors fast. The roof protects everything below it.

In wildfire areas, the roof is a main path for embers to ignite a building. California sets a fire class for that reason.

The roof also affects looks, height limits and solar. A steep roof adds height. A flat roof keeps the unit low but needs careful drainage.

Common ADU roof coverings

Roof fire classes explained

Sources: [1]

How the roof goes on

1. The roof frame is finished and inspected with the rest of the framing.
2. Sheathing is nailed to the frame.
3. Underlayment is laid, with any ice or water barrier the design calls for.
4. Drip edge and flashing go in at edges, walls, vents and skylights.
5. The covering is installed to the maker's instructions and its listing.
6. Vents, gutters and any solar mounts are added.
7. The building inspector checks the roof as the permit requires.

The diagram shows the finished roof from the outside in. Each layer protects the one below it, so a gap in any one of them can let water reach the frame.

Example: picking a roof on a hillside lot

A hypothetical detached ADU in a mapped California Fire Hazard Severity Zone. This shows the decision path, not a price.

The order matters: fire rule first, slope second, solar and looks after. For wildfire context see ADU fire code requirements.

Where you will see it

• Roof plan. Slope, material, drains and vents, in the plan set.
• Wildfire notes. In hazard zones, the plans list the Class A assembly and ember-resistant vents.
• Product data. The maker's listing shows the fire class and install rules.
• A bid. Roofing may be one line or split into underlayment, covering and flashing.
• Solar plans. Panel layout and mounts, where solar is included.

Rules: California first, then other states

California wildfire rule. The State Fire Marshal's rulemaking for California Residential Code Section R337.5 states that all roof assemblies in any Fire Hazard Severity Zone shall be Class A when tested to ASTM E108 or UL 790.

California Building Code Chapter 7A carries the same wildfire rules for buildings under that code. Check the current 2025 edition with your building department.

Is my lot in a zone? Fire Hazard Severity Zones are mapped by the State Fire Marshal and adopted locally. Ask your building department or check the state map.

California energy code. The 2025 Building Energy Efficiency Standards apply to permit applications made on or after 1 January 2026. Roof insulation and any solar rule for an ADU come from there; see ADU solar requirements.

The model code. The 2024 IRC covers roofs in Chapter 9: R902 Fire classification, R903 Weather protection, R905 Requirements for roof coverings, R907 Rooftop-mounted photovoltaic panel systems and R908 Reroofing.

Other states. Fire and wind rules vary widely. See ADU laws by state.

The guide below puts the California rules in the order you check them. The fire rule comes first because it can rule out a material before looks or price come up.

Sources: [1] [2] [3] [4]

What drives the cost

This page gives cost drivers, not prices.

The drivers are roof area, slope, material, the number of edges and openings, fire-rated parts in hazard zones, gutters and access. Tile adds weight, so the frame may cost more too. Solar mounts add flashing work.

Roofing is a hard cost. The cost calculator helps you budget it with the rest.

A low-slope roof: benefits and limits

Roofing compared with related terms

Common misreadings

Myth "Any shingle meets the wildfire rule."

Reality The rule is about a Class A rated assembly. Check the product listing and install method ¹.

Myth "The fire class is about the material alone."

Reality It is the tested roof assembly, installed to its listing ¹.

Myth "Shingles work on any roof."

Reality Shingles need enough slope. Near-flat roofs need low-slope products ².

Myth "Solar can be added anywhere later."

Reality Panels need structure, space and flashing. Planning early is simpler.

What to ask your roofer or designer

• Is my lot in a Fire Hazard Severity Zone?
• What fire class is this roof assembly, and where is the listing?
• Is the slope right for this material?
• How will flashing handle walls, vents and skylights?
• Will this roof carry solar? Where will the panels go?
• What warranty comes with the material and the labor?
• Is the roofer licensed? (In California, C-39 or B; check CSLB.)

Checklist for your project

1. Check your fire hazard zone status.
2. Pick a roof shape that fits the height limit.
3. Choose a covering rated for the zone and the slope.
4. Plan solar mounts and roof space early.
5. Ask for the product listing and keep it.
6. Confirm the roofer's license and insurance.
7. Keep the warranty papers and inspection record.

Upkeep and warning signs

A roof lasts longer with simple care. These checks are for looking, from the ground or a window. Leave climbing and repairs to a licensed roofer.

• Keep gutters and valleys clear of leaves, especially in wildfire areas where dry debris can catch embers.
• Look for missing, curled or cracked shingles or tiles after storms.
• Watch ceilings for stains, which can point to a leak.
• Check that vents keep their screens. In fire zones, vents are designed to resist embers.
• Trim branches that hang over the roof.
• After solar is installed, check around mounts for stains inside.

Roofing, wildfire and insurance

Insurers look at roofs closely in wildfire areas. A rated roof and clean gutters are part of what many of them ask about. Rules and discounts differ by insurer, so ask yours.

Keep the product listing and the final inspection record. They show what was installed if an insurer, buyer or lender asks. See insuring an ADU for more.

Related guides, tools and research

• ADUs and wildfire rebuilding
• ADU cost statistics
• ADU construction hub
• ADU design hub
• Size envelope calculatorCheck height and footprint

Related terms

ADU Framing

ADU framing is the structural skeleton of an accessory dwelling unit: the walls, floor and roof members, usually wood studs, joists and rafters or trusses, that hold the building up and resist wind and earthquakes.

ADU Insulation

Thermal insulation in an ADU's walls, roof and floor. In California, new ADUs must meet the Title 24 energy code, which sets insulation levels by climate zone.

Height Limit

A height limit is the maximum vertical height a zoning code allows for a building, measured from a reference point on the ground to a reference point on the roof that the local code defines.

ADU Hard Costs

ADU hard costs are the money spent physically building an accessory dwelling unit: site preparation, foundation, framing, roofing, windows, mechanical, electrical and plumbing systems, finishes, and the trenching that brings utilities to the unit, together with the contractor’s labor, overhead and profit.

California Residential Code

The California Residential Code (CRC) is Part 2.5 of Title 24 of the California Code of Regulations: the state building code for detached one- and two-family dwellings and townhouses, which is the code most ADUs in California are designed under.

ADU HVAC

ADU HVAC is the heating, ventilation and air-conditioning system of an accessory dwelling unit.

ADU Contractor

An ADU contractor is a licensed construction business that contracts to build an accessory dwelling unit, either doing the work itself or running the subcontractors who do the trades.

Also referenced from: ADU Framing, ADU HVAC