Dual-pane versus tempered windows

Dual-pane and tempered are not the same rule. Oregon R327, where adopted, allows tempered glass, multilayered glazed panels, glass block, or a 20-minute fire rating. California CWUIC wants multilayered panels with at least one tempered pane, or glass block, a 20-minute rating, or an SFM 12-7A-2 listed window. Energy-code dual-pane can meet Oregon’s multilayered option. It does not meet California’s tempered-pane rule by itself.

You are looking at a window schedule. Dual-pane is layers. Tempered is heat treatment. Oregon R327 lists them as separate options. California usually wants a tempered pane in the stack.

Read windows and Oregon R327 versus California CWUIC before you copy a California window spec onto an Oregon drawing, or the reverse.

Why it matters

Radiant heat breaks windows before flame reaches the wall. Broken glass is an ember path into the room. CAL FIRE calls single-pane and large windows particularly vulnerable. It tells homeowners to upgrade to dual-pane tempered glass. It says tempered glass is about four times more resistant to breaking during a wildfire. Keep vegetation off the glass. Combustible plants, mulch, or furniture under the sill make failure more likely. Zone 0 at the window is part of the same job as the glass. See landscaping and ember versus flame versus radiant heat.

That is home-hardening guidance. It is not Oregon R327, and it is not automatically a listing.

Skylights and glazed doors sit in the same code sections as windows. Do not treat the wall units as the whole job. Solid swinging entry doors are a different object. See doors.

Open windows are an ember path. Close them if you leave.

How it works

Dual-pane and tempered are two different facts. Do not swap them for variety.

Dual-pane means two or more lites in one unit. Codes also say multilayered glazed panels. California Safer from Wildfires says multipane. Same idea. Energy code is why most new residential glass is already dual-pane. The outer pane takes the heat first.

Tempered means a lite was heat-treated. It is a property of a pane, not a synonym for dual-pane. You can have dual-pane with two annealed lites. You can have one tempered lite in a dual-pane unit. You can have both panes tempered. Look for the etching in a corner.

SFM Standard 12-7A-2 is a test method for exterior windows. A 150 kW burner at the sill runs for eight minutes. A pass means that specimen did not let flame through the frame or pane, and the frame and pane did not fail structurally. The fixture limits specimen width to 3 feet. A pass is not a dual-pane energy sticker. It is not a 20-minute fire-protection rating. See SFM 12-7A-2.

OSFM listing category 8120 is the listing-body record for models that took that path. The listing is for a model, not a brand name. See how to read a listing and listing is voluntary.

The rules

1. Prescriptive path in Oregon. Adopted code R327.3.6, where a city or county has adopted R327, allows tempered glass, multilayered glazed panels, glass block, or a 20-minute fire rating. Those are or options. Dual-pane energy-code windows are the multilayered option. You do not need both dual-pane and tempered to meet that floor. Deschutes County’s R327 page names double-pane windows as a commonly used fire-hardening material. Confirm with the building official. Oregon-only.

2. Prescriptive path in California. CWUIC 504.8 wants multilayered glazed panels with at least one pane of tempered glass (complying with California Building Code Section 2406), or glass block, or glazing with a fire-protection rating of not less than 20 minutes, or glazing meeting SFM Standard 12-7A-2. People still search Chapter 7A. The live book is CWUIC.

3. Performance path. A window assembly that meets SFM 12-7A-2 and appears on an OSFM category 8120 listing. Listing is for a model. It is voluntary for most WUI products. Missing from the handbook is not an automatic ban. Presence is not an automatic permit.

4. Insurance and retrofit guidance. CAL FIRE home hardening recommends dual-pane tempered, metal frames where you can get them, and a check that vinyl units have a reinforcement bar in the separator member. Safer from Wildfires credits multipane windows as a California insurance measure. It is not Oregon insurance law. See insurance measures and Safer from Wildfires is not Oregon law. IBHS Wildfire Prepared Enhanced specifies dual-pane glass with tempered panes in both, or 20-minute glass, or glass block. Essential is the ember package (roof, vents, Zone 0). IBHS is not adopted code. See IBHS does not replace adopted code.

Do not tell a California client that energy-code dual-pane satisfies WUI glazing because it satisfies Oregon R327. Read Oregon R327 versus California CWUIC.

Glazed doors, sliding glass, and windows in doors sit in the same Oregon R327.3.6 and California CWUIC 504.8 lists as windows. Solid swinging entry doors are a different object. Exterior door leaves sit in OSFM category 8150. Read doors.

R327 is not a window-replacement code for every existing house. Oregon BCD’s local-adoption FAQ says R327 applies to new construction of new buildings, not typical roofing or siding swaps on older structures. Typical additions and element swaps on older dwellings are out, unless that dwelling was originally built to R327. Deschutes County says the same for typical additions. The authority having jurisdiction still decides the job in front of them. IBHS and CAL FIRE can still ask for the retrofit.

Deschutes County will accept OSFM handbook products when they are shown on the drawings. See show the product on the drawings.

What people mix up

• Calling dual-pane and tempered the same product.
• Importing California’s “at least one tempered pane” into an Oregon R327 drawing when the official did not ask for it.
• Importing Oregon’s energy-code dual-pane path into a California CWUIC job.
• Treating metal insect screens as a substitute for the glass rule. CAL FIRE says screens can help under radiant heat. They do not replace the glazing type.
• Treating every vinyl frame as an automatic fail. CAL FIRE flags vinyl without a reinforcement bar. R327 does not ban vinyl frames.
• Specifying “WUI windows” as a brand. Spec the path and, if you use the listing path, the model.
• Assuming every vinyl dual-pane unit is OSFM 8120 listed. Almost none are. The handbook currently has a short 8120 list.
• Using IBHS Essential as a window spec. Enhanced is the dual-tempered line.
• Calling dual-pane a “fire-rated window.” A 20-minute rating is a different path. A 12-7A-2 pass is not a 20-minute rating.
• Using an 8120 listing as a door-leaf spec. Category 8150 is the door leaf. Glazing in a door still follows the window list. See doors.
• Ignoring skylights. R327 and CWUIC include them. Plastic domes and operable units without mesh are a separate failure. CAL FIRE and CWUIC want 1/8 inch noncombustible mesh on operable skylights.
• Leaving combustibles under the glass and calling the unit hardened.

How to check

Walk the house. Note every exterior pane, sliding door, and skylight. Single-pane versus dual-pane is visible at the edge of the sash. Tempered glass usually has a corner etching. If you cannot see an etching, do not write “tempered” on the drawing. Note plastic dome skylights and operable units without mesh. Note large lites facing fuel. Note plants, mulch, and furniture under the sill.

Then read the adopted code for the lot. If none, you are in voluntary hardening or an insurer checklist.

If you take the listed path, open the product record, then the listing URL. This site has two OSFM 8120 records from the 2025 handbook: 8120-2120:0100 (metal-glazed unit with structural silicone glazing and 1/4 inch minimum laminated annealed glass, or an insulating unit with at least one tempered pane) and 8120-2120:0500 (thermal-break frame, 36 by 42 inch section, triple-layer laminated annealed glass). Confirm the live GOVmotus record and the exact model. Put that model on the drawing. Deschutes County accepts handbook products when they are shown on the drawings. Do not invent a listing ID for a big-box dual-pane unit that is not on the handbook. Do not scale a 3-foot specimen to every lite on the house without reading the listing.

Limits

This page does not stamp your permit. It does not rate U-factor, SHGC, or egress. It does not make the house fireproof. Two 8120 records are not a shopping catalog. Do not invent other listing IDs. Most energy-code windows never appear in OSFM category 8120, and they do not need to when the prescriptive path is the rule in force. SFM 12-7A-2 tests a window assembly in a fixture. It does not test every skylight geometry, every sliding-door size, or every aftermarket film. R327, where adopted, is new-construction scope unless the local department says otherwise. FireApproved is not the listing body and not the official.

Related records

• Windows
• Doors
• SFM 12-7A-2
• OSFM BML
• Safer from Wildfires
• IBHS Wildfire Prepared
• Oregon R327 versus California CWUIC
• How to read a listing
• Listing is voluntary