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How an intumescent vent closes
An intumescent vent is a listed assembly that includes a strip or coated matrix that swells when heated. That core is not Oregon’s 1/16 to 1/8 inch mesh path, even when the same unit also contains 1/16 inch wire. ICC-ES ESL-1689 describes 26-gauge G90 galvanized steel, an intumescent strip, and 1/16 inch wire mesh as construction inside BrandGuard’s ASTM E2886 listing. Vulcan’s OSFM row 8165-2192:0500 names a hexagonal aluminum matrix with an intumescent coating under the louver cap.
You are holding a vent that looks like a louver. Inside is a strip or a honeycomb. The listing is the model, not the chemistry brand.
The swell-sequence drawing (MECH-007) is not published yet. How to walk ESL-1689 lives on how to read an ICC-ES report. Do not use a house-level hub graphic as this mechanism.
Why it matters
Embers and flame at a vent are a hole problem. Mesh is a size. A baffle turns the path. An intumescent core is supposed to swell and choke that path when it gets hot. Those are different objects. Painting a coating on wood siding is a different object again, and it is not an R327.3.3 wall path. See the coatings finding.
How it works
In normal weather the unit is a ventilation opening. The listing tests ember intrusion and flame intrusion on that specimen, in the orientations Table 1 or the handbook row names. This page does not invent a swell temperature, a close time, or an airflow curve. Those numbers, if they exist, live in the listing or the manufacturer’s instructions.
ESL-1689 still contains 1/16 inch wire. That mesh is part of the listed construction. It is not a reason to skip the listing and call the unit Oregon’s prescriptive mesh path.
The paths
| Path | What you spec | What it is not |
|---|---|---|
| Prescriptive mesh | 1/16–1/8 inch noncombustible corrosion-resistant metal mesh, tight to the frame | An intumescent strip |
| Listed assembly with intumescent core | The model on ESL-1689 Table 1 or on the 8165 row | “Intumescent vents” as a brand |
| Listed assembly with a baffle, no swell strip | The model the listing actually describes | This page’s chemistry |
| Coatings on siding or a field-applied vent paint | Not an R327 wall path. Not an 8165 vent | This product |
See mesh versus listed vents. Put the model on the drawings. See show the product on the drawings.
What people mix up
- Treating the 1/16 inch mesh inside ESL-1689 as Oregon’s mesh-only path.
- Painting intumescent coating on an ordinary louver.
- Specifying “BrandGuard” from the ESL header instead of a Table 1 model.
- Assuming every 8165 row is intumescent.
- Inventing a close time this page did not open.
How to check
- Open the listing PDF or handbook row. Find the word intumescent, or a baffle, or mesh only.
- Match the model string and the orientation (gable, soffit, eave, foundation).
- Do not use a ridge or off-ridge hole as an E2886 specimen. See ridge vents versus ASTM E2886.
- If someone proposes a field-applied coating, that is a different conversation. See spray-FRT special inspection.
Limits
This page does not reprint ESL-1689 Table 1. It does not rate airflow. MECH-007 is not published. FireApproved is not the AHJ. A listing is not a permit.
Related records
Questions
Is the intumescent strip the same as 1/8 inch mesh?
No. Mesh size is a prescriptive path. An intumescent core is part of a listed assembly tested, for these products, to ASTM E2886. ESL-1689 describes 26-gauge G90 galvanized steel, an intumescent strip, and 1/16 inch wire mesh as construction inside that listed vent. The mesh in the box is not Oregon’s standalone mesh path.
Does it stay open for attic airflow until a fire?
The product is a ventilation opening in normal use. The listing is about ember intrusion and flame intrusion in the lab. This page does not invent a swell temperature or a close time. Read the listing and the manufacturer’s instructions.
Can I paint intumescent coating on an ordinary louver and call it listed?
No. Coatings are not an R327.3.3 wall path, and they are not an 8165 vent. A listed vent is a model. See the coatings finding and spray-FRT special inspection.
Is every 8165 vent intumescent?
No. Some listed vents use baffles, mesh, or a coated matrix. Vulcan’s 8165-2192:0500 handbook row names a hexagonal aluminum matrix with an intumescent coating. BrandGuard’s ESL-1689 names an intumescent strip. Read the row you spec.