Covering versus assembly

A roof covering is the visible layer. An assembly is covering plus underlayment plus deck, as tested. Class A, B, and C describe that assembly under ASTM E108 or UL 790. They do not live in a bag of shingles. Oregon R327, where adopted, uses a Class B-rated assembly floor. California CWUIC 504.2 requires Class A. IBHS Essential asks for a Class A covering. Spec the assembly, not the covering as if it carried the class.

You are writing a roof note. If you only name the shingle, you have not named the assembly the test used. Class lives on that assembly.

Why it matters

Embers land on the roof, in valleys, and in debris at the edge. CAL FIRE calls the roof the most vulnerable part of the home. The class on a drawing is how that roof is supposed to behave under burning brands, flame, and spread of flame. If you write only the covering, the building official cannot tell what was tested. The crew cannot tell what to install. The insurer’s photo set cannot tell a Class A covering from a Class A hope. See roofing.

Covering is not the assembly

Do not swap these words for variety.

ASTM E108 / UL 790 is the test method. The letters describe how that assembly behaves.

• Class A is the most severe test exposure.
• Class B is the middle.
• Class C is the least.

If the covering sits off the deck (tile profile, standing seam), the gap is part of the assembly. Oregon R327.3, where adopted, tells you to close that space against flames and embers, fireblock it, or install one layer of minimum 72-pound mineral-surfaced nonperforated ASTM D3909 cap sheet over the combustible deck (amendment PDF). The covering alone does not close the gap.

OSFM handbook category 8180 is non-wood roof covering and assemblies for the WUI. Rows often say “Class A roof covering.” Read the DESIGN line. The listing is a model plus the deck, underlayment, slope, and fastening the handbook names. Confirm the live GOVmotus record. See how to read a listing.

Same covering family, different assemblies:

• Metal Sales Image II 8180-2299:0500 names 15/32 inch plywood, felt, and two layers of VersaShield.
• Metal Sales Image II 8180-2299:0501 names 7/16 inch OSB and DensDeck.

An underlayment row is not a finished roof. Owens Corning Titanium FR (8180-2372:0001) and Polyglass Polystick XFR (8180-2305:0503) sit in named Class A systems. They are not a covering specification by themselves.

Which document you are answering

These documents are not synonyms.

1. Oregon R327.3, where adopted. Use asphalt shingles, slate, metal, or tile, clay, or concrete shingles per Chapter 9, or other roofing the building official deems equivalent to a minimum Class B-rated roof assembly. Wood shingle and shake roofs are not permitted. Close profile gaps as the section names. Valley flashing has a named metal and cap-sheet detail. Full text is in the amendment PDF. Oregon versus California is the R327 versus CWUIC guide.

2. California construction in mapped fire hazard areas. CWUIC 504.2 requires a Class A roof assembly tested to ASTM E108 or UL 790. Named exceptions treat some masonry, metal, tile, and slate assemblies as Class A without that test. Read the live section. Do not import Oregon’s Class B floor onto a California drawing.

3. California listing path. Models that OSFM has listed sit in category 8180. Listing remains voluntary for most WUI products. Absence from the handbook is not an automatic ban. Presence is not an automatic permit. See OSFM BML.

4. Insurer and HOA extras. IBHS Wildfire Prepared Essential wants a Class A covering and a clean roof. California Safer from Wildfires credits a Class A covering. That is covering language on an insurance list. The lab still tests an assembly. An HOA can require Class A where the code floor is Class B. Spec the stricter roof if you need both. IBHS does not replace adopted code. Safer from Wildfires is not Oregon law.

5. Clark County’s local 2024 IWUIC. Ordinance 5320 adopts the model in full except for its listed amendments; those amendments do not alter Chapter 5. The reviewed crosswalk therefore keeps Class A for IR1/IR2 and Class B or better for IR3. That is a local County path after the official WUI map and IR class are resolved, not a Nevada statewide Class A rule. See Clark County IWUIC over Nevada.

Ashland adds a local reroof sentence that should not be over-normalized. The City FAQ says replacement of 50 percent or more requires non-wood Class A or B fire-rated roofing material. That identifies a trigger and a class floor in homeowner language; it does not identify the deck, underlayment, covering, or listing for the tested assembly. Put those parts on the drawing and confirm the permit path with the City.

If you are building in unincorporated Deschutes County, you must meet R327. You may also be trying to satisfy IBHS or an HOA. Spec Class A if you need both. Do not tell the owner that R327 “requires Class A.” It does not. Deschutes County names Class B or better asphalt shingles as a common material. “Or better” is Class A. It is not a mandate to exceed the floor. Handbook products count only if you show them on the drawings.

What people mix up

• Writing “Class A shingles” as if the class lived in the granule.

• Treating a handbook line that says “Class A roof covering” as a bag-only spec. The DESIGN line still names deck and underlayment.

• Treating metal as automatically Class A.

• Telling an Oregon plans examiner that R327 requires Class A, or telling a California client that Class B meets CWUIC 504.2.

• Treating a wood-look composite shake as a wood shake. Westlake DaVinci 8180-2272:0500 is a composite shake and slate listed as a Class A assembly with a named plywood deck and Solarhide underlayment. R327 bans wood shingles and shakes. It does not ban every product that looks like a shake. Confirm the model.

• Treating an underlayment listing as a finished roof.

• Calling an ASTM E84 flame-spread class on siding a Class A roof. Roof class is a different test on a different assembly. See siding and ASTM E84.

• Treating a dirty Class A roof as a passed IBHS item. Cleaning debris is maintenance. Replacement is a permit conversation. See gutters.

• Saying a Class A roof finishes the edge. Debris still burns in the gutter. Open eaves are a different rule. See eaves.

• Reading “OSFM listed” as an Oregon permit. The building official still stamps the job.

How to check

Note the covering. Shake, composition, metal, tile, built-up. Look for debris in valleys and gutters. Look at the edge and the wall intersection. Look for gaps where the covering lifts, and for profile gaps between tile or metal and the deck.

Then read the adopted code for the lot.

1. If R327 applies, you need a Class B-rated assembly equivalent, no wood shake or wood shingle, and the gap and valley details in R327.3.
2. If CWUIC applies, you need a Class A assembly under 504.2 unless a named exception fits.
3. If the owner also wants an IBHS designation, Essential is Class A plus a clean roof. Spec the assembly that earns that class.
4. If you spec a listed model, open the product page, then the listing URL. Match the listing ID, the model, the deck, the underlayment, and the slope. Do not spec from a screenshot.
5. Put the same manufacturer, model, and listing program on the drawing. A brand name is not an assembly.

This site lists example 8180 records as records. It does not tell you they are legal on your lot.

Limits

This page does not pick a shingle. It does not rate hail, snow, or solar. It does not make the house fireproof. Absence from the handbook is not an automatic ban. Presence is not an automatic permit. It does not decide what your building official will stamp. R327, where adopted, is a new-construction code. CAL FIRE’s homeowner page is guidance, not Oregon law. FireApproved is not the listing body and not the official.

Related records

• Wildfire roofing
• ASTM E108 / UL 790
• OSFM Building Materials Listing
• Oregon R327 versus California CWUIC
• How to read a listing
• Show the product on the drawings
• IBHS does not replace adopted code