Existing building or New Building

[Tim Mailloux]

My office is starting work on a renovation of an existing 4 story office building. The scope of the project is to rip off the entire exterior skin, gut the interior, provide a new façade, all new MEP systems, new toilet cores and interior offices. Basically the only thing being saved is the steel structure, floor slabs and stairs if they are up to current code.


My gut tells me that we should use the IBC for the project and treat this as a new building. But using the IEBC might give us some leeway with the existing structural system. Seeing how we are reusing so little of the existing building at what point does the IEBC no longer apply to this “existing building”?

 

[RLGA]

Since this is an existing building, then you would start with the IEBC regardless. Assuming the building is currently an office building (i.e., Group B), thus no change of occupancy, then the work is purely an alteration, unless you're planning to add square-footage, then the addition requirements come into play. All new work needs to comply with the IBC, so the only thing really subject to the IEBC requirements will be the structural frame.

Using the Prescriptive Compliance Methods, Sections 403.3, 403.4, and 403.9 address existing structural elements. The IEBC allows allows increasing the design gravity loads by 5% without modification and for lateral loads a 10% increase is permitted without alteration.

Using the Work Area Compliance Method, Chapter 9 for Level 3 Alterations (which includes Chapters 7 and 8 for Levels 1 and 2, respectively) would be applicable. Sections 907.3 and 907.4 are specifically for structural elements and partially reference Chapter 8. Section 807 generally replicates the requirements for the Prescriptive Compliance Method.

(Edit: BTW, I'm assuming the 2015 IEBC, section references may be different for another edition)

 

[RJJ]

I would agree with the outline RLGA gives.

 

[JBI]

The only addition to Ron's post would be to point out that the Performance method would probably not provide any more relief in this case due to the extent of the work being proposed.

 

[steveray]

Level 3...Ron is correct as usual...Even a 99% "remodel" is level 3 and not "remodel to new".....The structural stuff "upgrades" falls into changing of loading or forces increased by more than 20% if I remember correctly.

 

[steveray]

807.5 Existing structural elements resisting lateral
loads. Alterations affecting the demands or capacities of
existing elements of the lateral load-resisting system shall be
evaluated using the wind provisions of the International
Building Code and the reduced IBC-level seismic forces. Any
existing lateral load-resisting structural elements whose
demand-capacity ratio with the alteration considered is more
than 10 percent greater than its demand-capacity ratio with
the alteration ignored shall be brought into compliance with
those wind and seismic provisions. In addition, the alteration
shall not create a structural irregularity prohibited by ASCE 7
unless the entire structure complies with Section
301.1.4.2. For the purposes of this section, comparisons of
demand-capacity ratios and calculation of design lateral
loads, forces and capacity shall account for the cumulative
effects of additions and alterations since the original construction.

 

[steveray]

807.4 Existing structural elements carrying gravity
loads. Alterations shall not reduce the capacity of existing
gravity load-carrying structural elements unless it is demonstrated
that the elements have the capacity to carry the applicable
design gravity loads required by the International
Building Code. Existing structural elements supporting any
additional gravity loads as a result of the alterations, including
the effects of snow drift, shall comply with the International
Building Code.
Exceptions:
1. Structural elements whose stress is not increased by
more than 5 percent.
2. Buildings of Group R occupancy with not more than
five dwelling or sleeping units used solely for residential
purposes where the existing building and its
alteration comply with the conventional light-frame
construction methods of the International Building
Code or the provisions of the International Residential
Code.


MY bad...the 20% is plumbing fixtures....

 

[ADAguy]

How old is the original structure, riveted, welded or bolted steel; metal pan deck?