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Heavy timber and log walls under R327
Where Oregon R327 is adopted, heavy timber is a defined size, not a vibe. R327.2 says sawn lumber or glued-laminated wood with the smallest minimum nominal dimension of 4 inches. Walls or floors in that definition are planks splined, tongue-and-groove, or set close together and well spiked (amendment PDF). Log wall construction is a separate numbered wall path. Neither is ignition-resistant lumber, and neither is a coating.
You are looking at a 6x6 porch post and a 4x tail. One of those objects is named in the underfloor exception. The tail is an eave conversation. Do not mix them.
CMP-006’s wall-path menu lives on ignition-resistant versus noncombustible. This page is the timber and log rows. Do not use a house-level hub graphic as a log-wall detail.
Why it matters
A 4-inch smallest nominal dimension is a measured thing. If the smallest face is 2x, it is not this definition. Builders use “heavy timber” as praise. R327 uses it as a path and as an exception.
How the definition is used
| Where it appears | What it does | What it does not do |
|---|---|---|
| R327.2 definition | Sets 4-inch smallest nominal dimension; wall/floor plank rules | Make 2x “timber” |
| R327.3.3 item 3 | Heavy timber assembly as a wall path | Replace log walls |
| R327.3.3 item 4 | Log wall construction assembly | Replace heavy timber |
| R327.3.4.4 exception | Heavy timber structural columns and beams skip underfloor protection | Skip the walking surface or the wall |
| Eave tails | Not a numbered R327.3.4.1 item | Seminar 4x practice. See Craftsman eaves |
Noncombustible is ASTM E136. Ignition-resistant is the 30-minute tunnel. Timber is thickness.
The paths
1. Wall as heavy timber or log. Pick item 3 or item 4. Do not write “logs as heavy timber.” Covering extent still follows R327.3.3.1.
2. Underfloor columns and beams. If they meet the definition, R327.3.4.4 does not require the underside menu on those members. The rest of the underfloor still does. See the 12-foot rule and deck ledger.
3. Seminar porch posts. Presenters named heavy timber porch posts or posts wrapped with Hardie. Event testimony is not a BCD ruling.
4. Do not coat it into compliance. See the coatings finding.
What people mix up
- Calling 4x eave tails a numbered eave path.
- Treating log and heavy timber as synonyms.
- Using the column exception as a walking-surface pass.
- Staining 4x stock and calling it ignition-resistant.
How to check
- Measure the smallest nominal dimension. Four inches, or it is not this definition.
- Name which sentence you are using. Wall, floor, or underfloor exception.
- Put the size on the drawings. “Heavy timber” without a dimension is not a spec.
Limits
This page does not spec species, grade, or a log-profile listing. FireApproved is not the AHJ. CWUIC is a different book.
Related records
Questions
Is a 4x rafter tail the heavy-timber eave path?
R327.2’s heavy-timber definition is used for walls and floors, and heavy-timber columns and beams are excepted from underfloor protection. The numbered eave list is noncombustible, ignition-resistant, Type X, a one-hour assembly, or ASTM E2957. Seminar 4x tails are practice, not a fifth numbered eave item. See Craftsman eaves.
Is log construction the same as heavy timber?
No. R327.3.3 lists heavy timber assembly and log wall construction as separate numbered wall paths. Do not swap the words.
Does staining make timber ignition-resistant?
No. Ignition-resistant is an extended ASTM E84 or UL 723 run. Coatings are not an R327.3.3 path. See the coatings finding.