non-combustible framing over timber structure

We are planning on raising the a portion of the roof of on our penthouse bulkhead, but seem to have hit a snag with the code rule for framing the structure. The original building (a factory from 1900) has timber framing. It is our understanding that new structures need to framed in non-combustible materials (ie, steel). However, we are also being told that we can’t put non-combustible framing over combustible framing (the original timber framing). Obviously, we can’t take out the original wood support columns from the building . So, I have no idea how to solve this for DOB. We’ve hired a structural engineer to come by, but any advice would be greatly appreciated.

mzmisdacutljvesg

in General Discussion 9 years and 10 months ago

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mzmisdacutljvesg | 9 years and 9 months ago

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Thanks!! It looks like the columns (11″x11″) and beams (14″x14″) are all considered heavy timber with at least 1 hour fire rating.

We ran this by a consultant, and his response is:

The Existing Building is classified as ‘Old Code Class 3 Non-Fireproof’ per the existing CO (CO # 82862)
Required Fire Rating of Penthouse per C26-672 “Walls and Roof of incombustible (non-combustible) materials of at least 1-hour in Class 3-Non-Fireproof Structures”
In Mixed Construction, no Structural Element shall be supported by construction having a lower fire resistance rating than that required for the element to be supported.
Therefore supporting construction for the Penthouse shall be at least 1-hour (Existing Columns and Beams supporting the existing Penthouse are Heavy Timber).

It is our understanding that as Heavy Timber members, they have a 1-hour equivalent.
Therefore, in this Mixed Construction building, our opinion is that the 1-hr non-combustible Penthouse may be supported by existing Heavy Timber members, subject to review and approval by NYC-Department of Buildings.

JorgeF | 9 years and 9 months ago

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You referenced non combustible materials. It is not about combustible or non combustible so forget about that. It is about construction classification, wood construction is allowed with limitations in certain construction classifications. If your engineer does not know this hire another one. Heavy timber is allowed (with restrictions), wood roofs and floors are allowed (with restrictions). You need to determine the minimum required construction classification based on your building use, square footage, and number of stories.