Market Insight: Guest Articles
Seismic Retrofit Requirements and Their Triggers
by J. Edgar Fennie Jr. AIA
Co founder FENNIE+MEHL Architects
January 2005
When a tenant or building owner contemplates making changes or renovations to an existing building invariably the topic of code-required seismic upgrades comes up (or more specifically, alterations to strengthen the lateral resistance capacity of the building.) Most people want to know in advance of doing any design work, what the seismic requirements will be and what parts of the renovation project will trigger any seismic work. Be aware that the type of project you may be considering and scope of the anticipated alterations can trigger upgrades to the structural system, and your building permit application will need to include the seismic work as part of the scope of work covered by the permit.
The cost of this type of work can be significant, depending on a number of factors such as the age of the building and how inherently strong it is resisting earthquake forces, and the costs can be a “dealbreaker” in many leasing situations.
So how can a tenant get a clear answer on whether his or her Tenant Improvement project will trigger an upgrade? Unfortunately the simple answer is, “It depends.” The real answer needs more thorough analysis and you are advised to seek the help of a registered architect and/or structural engineer to ascertain the code requirements for your project. However, a discussion of the general concepts for the triggers and the requirements can be useful in reviewing potential lease spaces and their renovation requirements prior to selecting a potential building.
Building Code Requirements
The building code (which covers all new building construction, additions and renovations) is where the applicable seismic provisions are typically enforced. In addition to structural design requirements, the building code also covers fire resistance, disabled access and other life safety requirements [See the sidebar at the left].
Identify the jurisdiction
So to begin to answer the million-dollar seismic upgrade question, first we start with the project location and whether the building is under the jurisdiction of the local municipality. Certain building types are exempt from local building department review (and subsequently local amendments.) For instance, federally owned buildings are exempt from local review and the California Building Code (CBC). Hospitals and other types of medical facilities are generally not under the jurisdiction of the city or county where they are located, but rather they are reviewed by Office of Statewide Health Planning and Development (OSHPD.) Schools and other types of K-12 facilities are generally not under the jurisdiction of the local municipality but rather they are reviewed by State Fire Marshall’s Office (SFM.) State Office buildings are reviewed by the Office of the State Architect (OSA.) Prisons and other correctional facilities area reviewed by the California Board of Corrections, and so on.
So you must first identify accurately who actually owns the building and if the local building department has jurisdiction. If the building is located in San Francisco and is subject to the jurisdiction of San Francisco Department of Building Inspection, local building code amendments do enforce a more stringent set of seismic upgrade requirements and specific triggers depending on the scope of work and occupancy of the building [See San Francisco Requirements below]
Occupancy and Buildings covered by the CBC
The occupancy group classification of the building (or more simply, how it is used) determines which provisions of the building code apply, and is therefore important that the existing and intended uses are clearly ascertained. The CBC divides the regulations into two broad categories; by occupancy or use of the building, and construction type or what the building is made of. [This makes good sense; the life-safety qualities of any building are a function of how intensely the building is used (e.g., a warehouse with few people and no combustible items have fewer limitations than say a movie theater with lots of people and some highly combustible materials) along with how strong and fire resistant the main building materials are. For example highly combustible wood framed building has more restrictions than the virtually non-combustible concrete framed building.]
The seismic upgrade triggers included in the CBC are all tied to changes in occupancy or use [Title 24, Section 3401]. Therefore, if your building is covered by the CBC without local amendments you will need to determine the approved use of the building (e.g., how it was classified when it was permitted) and confirm that the intended use after the renovation are in the same group. [See sidebar at left]
The CBC states that an existing building will have to be “brought up to the current code” when a change of use is contemplated that intensifies the use (e.g., increase the number of occupants and/or the amount of combustible materials stored in the building.) This means that the building, as renovated, will have to meet all current strength requirements, and depending on the age of the existing building, this can be costly. This is due in part to the code-required strength levels that have been systematically increased over several decades as engineers have concluded through research data for recent earthquakes, that the expected force levels in potential earthquakes for our area are greater than previously anticipated.
Therefore, assuming your building was classified as Group B (or what was called Group B2 in prior versions) and the intended use falls clearly into one of the listed Group B uses, and the building is subject to the CBC without local amendments, no seismic strengthening will likely be triggered by the renovation work.
San Francisco Seismic Triggers
In San Francisco the building code has been amended to require building owners to upgrade their building(s) as they are renovated. The type and scope of the renovation will determine the amount of structural work required. However, when seismic work is triggered it typically does not have to meet the full strength levels as defined by the CBC which can significantly reduce the cost of the seismic work. [See San Francisco Structural Design Requirements vs. CBC Requirements below.]
There are many different triggers in San Francisco. Mainly they break down into three categories:
- Increase in building size or occupant load
- Structural modifications or repairs
- Extent of renovation
Increase in building size or occupant load: Assuming there is no change of use or occupant load, and if the building size is increased through a vertical addition, the new addition will likely have to meet the CBC requirements and the vertical load path from the addition to the foundation will have to be adequate to carry the new loads (Note that projects of Type V construction, and Group R occupancy which increase the Base Shear by less than 5% are exempted from the vertical load path requirements.)
Assuming there is no change of use or occupant load, and if the building size is increased through a horizontal addition, and the area of the horizontal addition is less than 30% or the original building area (as defined by SFBC 3403.2.1.1) only the new addition will likely have to meet the SFBC upgrade requirements with no upgrades required for the remainder of the building. Larger horizontal additions which are not isolated structurally from the original building structure will likely have to be built to CBC standards and the original building will likely have to meet SFBC upgrade requirements. If the structure of the new horizontal addition can be isolated, then only the new structure will likely have to meet CBC standards with no upgrade required for the original building.
If the anticipated project changes the use which in turn increases the occupant load by 10% and the occupant load for the building is more than 100, the entire building will likely have to meet the SFBC upgrade requirements.
Structural Modifications:Structural modifications are those which typically change columns, beams and shear walls or braces. If the structural work you would like to do is a repair of more than 20% these elements in the building (those members that have been damaged by earthquakes, fire, etc.) or 30% of the vertical load capacity is being repaired the entire building will likely have to meet the SFBC upgrade requirements.
If 30% or more of the existing structural framing is being modified for other reasons, the entire building will likely have to meet the SFBC upgrade requirements. Less than 30% will not likely trigger any upgrades.
It should be noted that seismic upgrades to the structural system, which are not triggered by a renovation or addition can be done on a voluntary basis and typically will not trigger other seismic requirements. The upgrades may trigger accessibility upgrades (or other life-safety requirements) and you should consult with a registered structural engineer and/or architect prior to proceeding on the design work.
Extent of Renovation: Depending on how much of the building is to be remodeled by the Tenant Improvement may trigger seismic upgrades. What is somewhat unique in this requirement is that the renovation work over the last two years is taken into account along with the renovation project in question. Be aware that it is possible that a small Tenant Improvement project on one floor of a multistory building could, where other projects have been completed over the last two years, trigger a full upgrade to the building. The trigger is defined as where 2/3 or more of the floors (excluding basements) in the building are “Substantially Altered” (e.g., partitions or ceilings are renovated or have been changed in the last two years). In this event the entire building will likely have to meet the SFBC upgrade requirements.
Assuming no change of use or occupancy, projects limited to one floor or less in a multistory building that has not seen any renovation activity for at least two years will likely not trigger any seismic upgrading.
San Francisco Structural Design Requirements vs. CBC Requirements
In the event your project must meet SFBC seismic requirements when triggered by a renovation or addition the force levels and other detailed standards contained in the current CBC have been relaxed somewhat. The main item is seismic force level is only 75% of the requirement in the CBC. Also, what is referred to as the Near field effect factor as required in the CBC to account for the proximity of active faults and the subsequent increase in force levels is held a 1.0 ( or no increase for nearby faults.) There are a number of other exceptions to the CBC that your engineer can take advantage of when designing seismic upgrade projects in San Francisco.
There are also a number of other minor exceptions and you may find that even your structural engineer may not have a clear picture on how the specific regulations apply to a particular project. In this event building permit applicants are encouraged to request their architects or engineers apply for a Pre-Plan Review meeting to discuss the project in detail with the building department officials. That way, the seismic triggering issues and the subsequent design requirements can be clarified and documented in writing, before proceeding with the construction documents and permit application. This will speed up the department plan review and avoid costly surprises and delays in the permit application process.
Also, it should be pointed out that, as written, the building code is a minimum standard, and therefore not only can you exceed the requirements contained therein, but you are encouraged to do so whenever feasible.
Hopefully, with the help of your architect or structural engineer the seismic upgrade issue can be identified and quantified early on in the design process so that all the parties to a lease will know their respective responsibilities and minimize their exposure to surprises in the Tenant Improvement process. And the earlier the question of whether a seismic upgrade will be triggered can be determined, the more time will be available to design cost-effective solutions to meet the requirements.
