The A2L Shaft Alternative Is in ASHRAE 15. Not in Printed CMC 1109.3

The industry is calling it the end of the A2L pipe shaft. Run refrigerant piping up through the floors of a multistory building and, for years, you had two choices: wrap it in a gastight, fire-resistive shaft, or route it on the exterior wall. On a low-GWP heat-pump retrofit — R-454B line sets threaded through an occupied building — that shaft is a real cost, sometimes the one that kills the job.

ASHRAE 15-2024, Addendum a, opens a third door. Here's the catch: the section that requires the shaft was never reprinted.

What the shaft rule actually says

Open the 2025 California Mechanical Code to Section 1109.3, Penetration of Piping. The baseline is blunt — refrigerant piping shall not penetrate floors, ceilings, or roofs. The exception that bites on a larger charge is Exception 5: in non-industrial occupancies, where the refrigerant concentration exceeds the Table 1102.3 value for the smallest occupied space the piping passes through, the penetration must be one of two things.

Verified against the 2025 CMC, §1109.3 Exception 5: penetrations must be "Enclosed by an approved gastight, fire-resistive duct or shaft with openings to those floors served by the refrigerating system," or "Located on the exterior wall of a building where vented to the outdoors." The code tags this provision [ASHRAE 15:8.10.3].

That bracket is the tell: CMC 1109.3 is California's reprint of the ASHRAE 15 shaft rule — the older edition's text, carried verbatim into the printed code.

What Addendum a changes

ASHRAE 15-2024, Addendum a adds a new provision: Section 9.12.1.5.1, "Shaft Alternative." It says a shaft enclosure is not required for the refrigerant piping of several listed system types. One is the case the industry wanted: continuous refrigerant pipe or tube — joints and connections included — tested in accordance with Section 9.13.

Test the line set, document it, and the shaft comes off the table. (The 9.13 test lives in the standard, which you will need to read.)

The industry coalition backing California's update said it plainly in the record: the current shaft-enclosure requirements "create major cost and retrofit barriers," and the alternative "removes the shaft requirement when piping is tested."

Where California actually stands

Here's the thing: California adopts ASHRAE 15 by reference. The edition is set in Chapter 18, Table 1801.1 — and today that row still reads 2022.

Verified against the 2025 CMC, Chapter 18 Table 1801.1: "ASHRAE 15-2022 | Safety Standard for Refrigeration Systems," referenced at 1102.1, 1104.6.1, and others.

The State Fire Marshal's 2025 Intervening Cycle package (SFM 02/25) proposes to change that one row — to "the 2024 edition of ASHRAE 15 … including Addendum A." The push is statutory: at the May 6, 2026 Commission meeting, industry noted that AB 209 (2022) directs the state to adopt the latest ASHRAE 15.

Two cautions on status. First, this is a proposed edition change in the express terms — not adopted. It went to the Commission for the cycle; confirm the recorded action before you rely on it. Second, at that May 6 meeting — which took no vote on the proposals — a commissioner questioned whether the flammable-refrigerant change fit AB 130's narrow exceptions. The record is what controls.

The edition update rides the State Fire Marshal's package, so it reaches the occupancies the SFM regulates. Whether the column that governs your project — BSC, HCD, DSA, or OSHPD — carries the same 2024-plus-Addendum-a edition is a separate question. Check the Chapter 18 matrix adoption table for your agency.

The reference moved. The printed section didn't.

Update the reference table and you have changed which edition of ASHRAE 15 the code points to. You have not changed the printed text of CMC 1109.3 Exception 5. It still requires the shaft.

So you have a chapter that demands both. CMC 1102.1 says refrigeration systems using a refrigerant other than ammonia "shall comply with this chapter and ASHRAE 15." That means the chapter (printed 1109.3, shaft required) and the standard (2024 with Addendum a, shaft optional if tested). When the two collide, the code has a tiebreaker.

Verified against the 2025 CMC, §102.1: "In instances where this code, applicable standards, or the manufacturer's installation instructions conflict, the more stringent provisions shall prevail."

Read that line before you design the shaft out. The printed 1109.3 is the more stringent provision. How your AHJ resolves it is their call — the call to get early.

What to do on a job now

• Document the Section 9.13 test. If you are leaning on the Shaft Alternative, the tested-piping condition is the whole basis. Build the test record into the submittal.
• Cite both sections. Put ASHRAE 15-2024 §9.12.1.5.1 and the printed CMC 1109.3 in front of the reviewer together, and name the 102.1 conflict yourself.
• Get an AHJ determination early. Do not assume a reference-table edition bump overrides the reprinted 1109.3 text. Ask before you detail it out.
• Confirm the edition for your agency in the Chapter 18 matrix, and verify local amendments with your jurisdiction. Not legal advice — just check before the shaft gets value-engineered off the drawings.

This is the same shape as the A2L concentration trap in the Table 1102.3 plan-check post, and the edition question behind it is the one in which edition of the referenced standards applies.

What CrossBeam does with it

CrossBeam reads refrigerant-piping submittals against both the referenced ASHRAE 15 edition and the printed CMC section that still requires the shaft, so a tested-piping design does not quietly assume the reference update rewrote 1109.3. It surfaces the conflict — and the 102.1 tiebreaker — before it turns into a corrections letter.