wood roof deck on Type I building

We have all seen wood decking used for exterior decks on non-combustible building roofs, but the code (2009 IBC in this case) does not explicitly allow this. Section 603 does not mention exterior decks (unless these could be considered as "floors") nor does Chapter 15.

On what code basis are exterior wood decks allowable?
Duane Jonlin, AIA
Original Post
Does 2009 IBC 1406.3 help in any way (refer to exception 1)?

1406.3: Balconies and similar projections of combustible construction other than fire-retardant-treated wood shall be fire-resistance rated in accordance with Table 601 for floor construction or shall be of Type IV construction in accordance with Section 602.4. The aggregate length shall not exceed 50 percent of the buildings perimeter on each floor.

Exceptions:

1. On buildings of Type I and II construction, three stories or less above grade plane, fire-retardant-treated wood shall be permitted for balconies, porches, decks and exterior stairways not used as required exits.
2. Untreated wood is permitted for pickets and rails or similar guardrail devices that are limited to 42 inches (1067 mm) in height.
3. Balconies and similar projections on buildings of Type III, IV and V construction shall be permitted to be of Type V construction, and shall not be required to have a fire-resistance rating where sprinkler protection is extended to these areas.
4. Where sprinkler protection is extended to the balcony areas, the aggregate length of the balcony on each floor shall not be limited.
Should clarify here that a "roof deck" by IBC definition is not the type of roof deck in which this thread is about. I suggest "roof patio deck" to make the distinction clear.

I would consider any type of roof patio decking on a roof be treated as a roof covering by IBC definition per Section 1502.1 (applied to roof for "appearance"). Therefore, it should comply with the required classifications per Table 1505.1 or be determined noncombustible by Chapter 7.

Why would the code restrict the type of roofing material but then permit a combustible roof patio deck? I don't think it does now and that it never had.
Duane,
Different fire exposure dynamics and fire attack considerations for interior floor to exterior roof covering, is the difference.

There are many "raw" wood decks on highrise roofs. Whether they are code compliant or not is another question. I know in SF that many roof decks were done without permit approvals, so the comparison for them existing is not a code approval basis.

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