FireApproved
On this page
  1. Why it matters
  2. How the split works
  3. The paths
  4. What people mix up
  5. How to check
  6. Limits
  7. Related records
  8. Sources

Home / Guides / Oregon R327 practice / When R327 hits an ADU, garage, or shop

When R327 hits an ADU, garage, or shop

Last verified 2026-08-27.

This page is Oregon law. See R327 remodels when the answer is no.

Where R327 is adopted, a new detached ADU is a new dwelling. A shop or garage follows the accessory-structure size and distance rules in Oregon BCD’s local-adoption FAQ. Do not invent the 400-square-foot or 50-foot numbers. They are in that FAQ and in R327.1.3. Confirm with the building official.

You are drawing a detached ADU or a shop. The ADU is a dwelling. The shop is an accessory structure with size and distance tests. Confirm both with the official.

Why it matters

People treat every outbuilding as “the house.” BCD splits accessory dwelling units from accessory structures. Getting the split wrong either over-builds a 12-by-12 shed or under-builds a 600-square-foot shop next to the house.

How the split works

BCD’s local-adoption FAQ is the public document for this. It is not a glazing FAQ. It is scope.

ADU. For the ORSC, an accessory dwelling unit is regulated the same as the primary dwelling. It is not an “accessory structure” in that FAQ.

Accessory structure. Incidental supportive uses. BCD names detached garages, carports, storage sheds, tool sheds, shops, and garden structures. Sleeping or permanent cooking makes the building habitable.

The paths

1. New detached ADU. Newly constructed. Subject to R327 as a newly constructed dwelling. Same roof, wall, vent, and eave rules as the house.

2. ADU attached as an addition to an existing dwelling. BCD says that addition is not subject to R327. If the existing dwelling was originally built to R327, later additions are subject. See remodels when the answer is no.

3. Habitable accessory structure. Any size, any location on the lot. In.

4. Nonhabitable accessory structure greater than 400 square feet. In.

5. Nonhabitable accessory structure of any size within 50 feet of other structures on the lot that contain habitable space. In. A small shop next to the house is in.

6. Outside, if all of these are true. Nonhabitable, 400 square feet or less, and 50 feet or more from habitable structures on the lot. Also out: structures existing at local adoption, structures exempted under ORS 455.315, and detached membrane-covered frame structures as defined.

R327.1.3 Exception 1 matches the 400-square-foot and 50-foot idea (amendment PDF).

Deschutes County also names a 15-foot maximum roof height for a small non-habitable detached accessory. That height sentence is on the county page. BCD’s FAQ does not print that height. Do not paste it statewide. Ask the county.

In Grants Pass, Municipal Code §§9.04.010 and 9.04.200 supply the local adoption and new-construction bridge. They do not turn every new outbuilding at a Grants Pass mailing address into an R327 project. Apply the dwelling and accessory-structure tests above, then ask Building Division whether the site and project meet the local wildfire-zone trigger.

What people mix up

  • Calling the ADU a shed so it skips R327.
  • Measuring 400 square feet and ignoring the 50-foot rule.
  • Treating a manufactured home as the habitable structure that pulls the shop in, or as R327 itself. Manufactured dwellings are outside R327.
  • Applying California CWUIC accessory rules on an Oregon lot. Read R327 versus CWUIC.
  • City doorway pages. National URL. Oregon facts stay in Where-this-differs.

How to check

  1. Is R327 adopted for the lot? See the adoption dataset.
  2. Is the building an ADU or an accessory structure? Use BCD’s definitions, not the marketing flyer.
  3. Habitable or not? Sleeping or permanent cooking counts.
  4. Floor area and distance to habitable space on the same lot.
  5. Put the result on the drawings. See show the product on the drawings.

Limits

This page does not stamp the permit. It does not decide a lot line or a covenant. It does not scrape community exhibits. BCD’s FAQ is the citation for the ADU and 400 / 50 numbers. The county height sentence is county practice until BCD prints it.

R327 versus CWUIC, remodels, manufactured homes, adoption dataset.

Sources

  1. BCD local-adoption FAQ (Oregon Building Codes Division)
  2. 2023 ORSC Section R327 amendment (Oregon BCD)
  3. Deschutes County Fire Hardening Requirements (R327)
  4. BCD wildfire hazard mitigation

Questions

Is an ADU an accessory structure?

No. Oregon BCD’s FAQ says that for the ORSC, accessory dwelling units are regulated the same as the primary dwelling. Accessory structures are incidental uses such as detached garages, shops, and sheds.

Does a new detached ADU have to meet R327?

Where R327 is adopted, a newly constructed detached ADU is a newly constructed dwelling. BCD says it is subject to R327. An ADU attached to an existing dwelling as an addition is not subject to R327, unless that dwelling was originally built to R327.

When does a shop or garage have to meet R327?

BCD says R327 applies to habitable accessory structures of any size, to nonhabitable accessory structures greater than 400 square feet, and to nonhabitable accessory structures of any size within 50 feet of other structures on the lot that contain habitable space. Smaller, farther, nonhabitable buildings can be outside. Confirm the numbers in the FAQ and with the official.

Does a manufactured home on the same lot pull the shop into R327?

Manufactured dwellings are outside ORSC and R327. The shop is still an accessory structure judged against other habitable structures on the lot. Ask the building official how they count that lot.

Sources