Difference Between Standard Mill and Semi-Mill?

What is the difference between Standard Mill and Semi-Mill Construction?

The annex of NFPA 13 lists Standard Mill as an example of unobstructed construction, while Semi-Mill is considered to be obstructed construction.

A.3.3.43.1 Obstructed Construction
(5) Semi-Mill Construction. The term semi-mill construction as used in this standard refers to a modified standard mill construction, where greater column spacing is used and beams rest on girders.

A.3.3.43.2 Unobstructed Construction.
(4) Standard Mill Construction. The term standard mill construction as used in this standard refers to heavy timber construction as defined in NFPA 220.

Semi-Mill in NFPA 13 is only defined as a modified standard mill construction where greater column spacing is used and beams rest on girders. The description of Standard Mill refers to heavy timber construction as defined in NFPA 220. NFPA 220 has nominal dimensions for structural members and other details, but that's it.

How should I know when something is Standard Mill or Semi-Mill under NFPA 13?

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