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Design Professionals Vs. Conventional Light Frame Construction
In California, is it necessary to have a professional design an apartment building? Usually, yes, but there are exceptions. For example, let’s look at the design required for a conventional two story apartment building with four dwelling units (I’ll chat more on conventional framing in a moment).
The Professional Engineers Act, Business and Professions CodeSec. section 5537 and the Act Regulating the Practice of Architecture require plans be prepared by a professional. Specifically, a Civil Engineer, Structural Engineer or Architect licensed and registered to practice in the State of California is to prepare the plans, drawings, specifications or instruments of service for any building or component that affects the safety of any building or its occupants, including but not limited to structural or seismic components. Exemptions to this section 5537 include conventional woodframe structures such as residential one and two story buildings up to four dwelling units, garages up to two stories and agricultural buildings.
This permits our two story apartment building to be designed by any person, so long as the plans meet minimum requirements (such as conventional design, legibility, scale and completeness). At least that’s the word from the Business and Professions CodeSec.. Now read Uniform Building Code section 1923.10.3; it says our apartment building is to have a reinforced foundation because structural plain concrete members are not permitted in seismic zone 3 and 4. Section 1923.10.3 exempts slabs on grade and footings of dwellings, lodging houses, small congregate residences, carports, garages, sheds and agricultural buildings, but not an apartment building.
The foundation reinforcing required in seismic zone 3 and 4 usually requires a design that only a professional can provide. Check with your local building department to see if they will allow a two story apartment building with four dwelling units to have a foundation reinforced by two #4 re-bar without a design professional. This is proposed with the understanding that conventional light frame construction will impose no unusual forces on a foundation.
Which leads us to the chat on conventional framing I promised. Business and Professions Code Sec.Sec. 5537 requires architects to prepare and sign any building plans, drawings or specifications except specified structures, as long as the Building Official deems there is no undue risk to the public health, safety or welfare and that any portion of any structure which deviates from substantial compliance with conventional framing will be prepared by a design professional.
Conventional light-frame construction is restricted to Group R Occupancies three stories or less, to interior nonload-bearing partitions, ceilings and curtain walls in all occupancies, and to specific uses listed in UBC Sec. 2326.1. A garage braced wall panel may be a minimum 2’-8" wide with a maximum 10’-0" panel height, according to UBC Sec. 2326.11.4.
In single story buildings, minimum conventional light-frame construction specified in UBC Table 23-I-W requires lateral bracing panels positioned on each end and not more than 25 feet on center of a single-story building’s interior and exterior braced wall lines. UBC Sec. 2326.4.1 limits the distance between these walls to a maximum of 34 feet (in both longitudinal and transverse directions).
In multiple story buildings, minimum conventional light-frame construction specified in UBC Table 23-I-W requires lateral bracing panels positioned on each end and not more than 25 feet on center of a building’s interior and exterior braced wall lines. Further, the first story of two story buildings and the second story of three story buildings are to be braced not less than 25% of the building length; the first story of three story buildings is to be braced not less than 40%. UBC Sec. 2326.4.1 limits the distance between these walls to a maximum of 34 feet (in both longitudinal and transverse directions). UBC Sec. 2326.5.6 requires at least one continuous foundation under an interior braced wall line at intervals not exceeding 50 feet.
When of unusual shape, UBC Sec. 2326.4.4. requires buildings of conventional light-frame construction to have a lateral-force-resisting system designed by an engineer in accordance with UBC Chapter 16. One or more of the following may be considered to constitute an unusual shape: Exterior braced wall panels out of plane vertically from foundation to uppermost story; A section of a roof or floor that is not supported on all four sides by braced wall lines; When a building does not have braced wall lines in two perpendicular directions; When an opening such as a doorway or window extends more than one foot under a required braced wall panel located above; In buildings where a floor or roof has an opening that exceeds the lesser of 12 feet or 50% of the least floor dimension, Construction where portions of a floor level are vertically offset such that the framing members on either side of the offset cannot be lapped or tied together in an approved manner as required by UBC Section 2326.8.3. Be sure to also see the many exceptions to the above requirements which can be found in UBC Sec. 2326.5.4.
Conventional framing does allow building permits to be obtained on plans which have not been designed by professionals, but be aware; know the limitations of conventional framing. If a portion of the project must exceed the limits, then obtain the services of a design professional and have them note on the front of the plans that there is an architect or engineer of record covering that portion. This will serve as a warning to any non-professionals who would inadvertently alter the design.
Robert Buss
