Does Solar Change Your Roof's Fire Rating? What the Code Actually Requires

A roof covering carries a fire classification — Class A, Class B or Class C — and that classification describes how it behaves when fire arrives from outside the building. An ember from a wildfire. A burning fragment off a neighbour's roof.

Put an array above that covering and you have changed the assembly. There is now a surface above the roof, an air gap between the two, and a set of materials that were not present when the roof was tested. The code's response is not to assume the change is harmless. It is to require the thing above the roof to carry a classification too.

What the classes mean

The classification comes from UL 790, also published as ASTM E108, the standard test methods for fire tests of roof coverings. It covers performance against simulated fire sources originating outside the building.

UL's own description of the three classes:

• Class A — effective against severe fire test exposures
• Class B — effective against moderate fire test exposures
• Class C — effective against light fire test exposures

Under those exposures, UL notes, the coverings afford a degree of fire protection to the roof deck, do not slip from position, and are not expected to produce flying brands. Two of the tests are worth picturing, because they explain what the rating is actually measuring:

• Burning brand. A burning wooden block is set on the assembly while a fan blows across it. Flame must not appear on the underside of the deck within the test period.
• Spread of flame. Flame is directed up the roof under the same fan. It must not travel beyond a set distance within the allotted time.

The classes are a ladder and it only runs downward. Because the Class A tests are more severe than Class B, which are more severe than Class C, a Class A assembly is suitable wherever Class A, B or C is required, and a Class B assembly wherever Class B or C is required. An unrated assembly is not suitable for any application requiring a class, except where a code specifically says so.

Where a class is required at all

Section R902.1 of the International Residential Code sets the trigger:

Class A, B or C roofing shall be installed in jurisdictions designated by law as requiring their use or where the edge of the roof is less than 3 feet from a lot line.

So the requirement is local. Wildland-urban interface areas and jurisdictions with a fire history commonly mandate Class A across the board. Elsewhere the trigger is proximity — a roof edge within three feet of a property line, which on a dense infill lot is the ordinary condition rather than the exception.

The same section carries exceptions that treat certain assemblies as Class A without further testing: brick, masonry and exposed concrete roof decks; ferrous or copper shingles or sheets, metal sheets and shingles, clay or concrete roof tile, or slate installed on noncombustible decks; minimum 16-ounce-per-square-foot copper sheets over combustible decks; and slate over underlayment over combustible decks.

Note the condition attached to the second exception. Tile and metal are Class A without testing on a noncombustible deck. On the ordinary plywood or OSB deck of a house, they are not carried by that exception, which is a detail that gets skipped when someone reasons that a tile roof must be fireproof because tile does not burn.

Because the trigger is jurisdictional, this belongs with the rest of the AHJ research at the start of a project — not in a conversation with a plan reviewer at the end of one.

The rating belongs to a system, not a module

This is the part that most often goes wrong on a submission.

Under the revised standards, fire classification applies to a photovoltaic system: the modules, the mounting hardware and the roof covering, evaluated together. Modules are assigned a fire Type based on their materials and construction. A mounting system is then tested with fire-Typed modules over a roof covering, and it is that combination which earns Class A, B or C.

UL's guidance to code officials states it directly: photovoltaic mounting systems are marked Class A, Class B or Class C to denote their resistance to external fire exposure when installed in combination with specific photovoltaic modules and according to the mounting system installation instructions.

Three consequences follow, and each one is a real rejection:

1. A module does not have a Class A rating by itself. A datasheet asserting one, with no system context, is not describing a rating the code recognises.
2. Substituting a module outside the listed Types breaks the claim. The Type system exists so that substitution within a Type is possible; substitution outside it is not.
3. Ignoring the mounting instructions breaks it too. Mount height, orientation and the deflector or skirt arrangement are part of what was tested. They are conditions, not preferences.

This is the same structure as the listing problem on rapid shutdown: equipment that is individually certified can still fail because the combination was never evaluated.

"UL 2703 listed" does not answer the question

UL is unusually blunt about this, in guidance written for the people doing plan review:

When conducting a PV plan review or PV installation inspection simply verifying that the component is UL Certified (Listed) to UL 2703 is insufficient.

The reason is that UL 2703 covers several different aspects of a mounting system. A product may be investigated for mechanical loading alone, for grounding and bonding alone, for a fire classification alone, or for some combination of those when used with specific modules. Only the certification record identifies which, and which components and installation criteria are required to achieve a given rating.

So on a plan set, "UL 2703 compliant" on a cut sheet answers a different question from the one being asked. The document that answers it is the listing, naming the module Types, the mounting components and the roof coverings the fire class was established with.

If your submissions are getting corrections on this, the listing reference belongs in the permit package alongside the datasheets, not behind them.

Which section applies depends on the edition

Plan reviewers cite the edition their jurisdiction has adopted, and this subject has moved.

The two rooftop formulations are not identical in emphasis. One anchors the system to whatever the roof assembly was required to be; the other requires the system to be tested and identified in its own right. In a jurisdiction requiring Class A they converge on the same answer. In a jurisdiction requiring nothing, the first arguably requires nothing of the array either — which is exactly the kind of divergence that makes citing the wrong edition expensive.

Confirm the section against the adopted edition. The same caution applies here as to the slope tables in Chapter 9: numbering moves, and jurisdictions amend.

Building-integrated is a different question

If the photovoltaic product is the weather surface — a solar shingle, a BIPV panel — it is not a system above a covering. It is the covering.

The code follows that logic. Building-integrated photovoltaic systems serving as roof coverings are directed to the covering requirements of Section R905, photovoltaic shingles to their own subsection within it, and the fire classification requirement to Section R902.3 rather than to the rooftop-mounted provision. Later editions have R902.3 require that building-integrated products installed as the covering be tested, listed and labeled for fire classification under a standard written for them.

The distinction is clean and worth holding onto: weather surface, judged as a covering; above the weather surface, judged as a system over a covering.

What a complete submission looks like

Four items, and a reviewer can check them in about a minute:

1. Is a class required here? Jurisdiction designation, or roof edge within three feet of a lot line. If neither, say so on the cover sheet rather than leaving it unaddressed.
2. What class does the roof covering hold? Either a tested classification or one of the R902.1 exceptions — and if via an exception, the deck condition it depends on.
3. Does the mounting system's listing carry a fire class, with the module in it? Not "is it listed" but "is it listed for this, with this module's Type."
4. Does the installation match the instructions the class was established under? Mount height, orientation, skirts or deflectors where the listing requires them.

Miss any one and the assembly may well perform fine. It just will not be demonstrated to, and a plan reviewer cannot approve a performance nobody documented. That is the same failure pattern behind most of the reasons permit applications get rejected: not bad engineering, but undocumented engineering.

The bottom line

A Class A roof does not stay Class A because it used to be. The moment an array sits above the covering, the thing the code is interested in is the combination — a fire-Typed module, a specific mounting system, and the roof covering underneath — and that combination has to have been evaluated together.

The requirement is local, so the first question is whether a class applies at all. The second is what the covering holds. The third is whether the listing on the mounting system names this module and this covering. None of those is difficult. All three are routinely left to the reviewer to discover.

Coverage is confirmed per service area rather than promised as blanket availability. If you want the fire classification settled inside the plan set instead of inside a correction notice, get in touch.