Unreinforced Masonry (URM) Buildings

Technical FAQs (Frequently Asked Questions)

The following technical questions are a compilation of inquiries made by you, our valued design professionals. They are presented here in our attempt to assist you with an explanation of the Building Code requirements and for better understanding of the requirements of City’s Unreinforced Masonry (URM) program.

Please be advised that the questions and answers presented herein are solely intended for use by civil - structural engineers / architects licensed by the State of California, who are responsible for the structural design of the seismic retrofit work for URM buildings per City’s URM Ordinance.

Note: Below is a list of references mentioned in the FAQs:

• URM Ordinance - San Diego Municipal Code (SDMC)
• California Building Code (CBC)
• Uniform Building Code (UBC)
• Uniform Code for Building Conservation (UCBC)

1. What is required to be done by the URM Ordinance?
2. In addition to the mandatory provisions, are there any other requirements?
3. Is it required to verify the capacity of the entire roof or floor diaphragm in order to comply with the mandatory provisions of Sec. 145.0410 of the URM Ordinance?
4. Is it required to verify the capacity of the entire roof or floor diaphragm shear transfer in order to comply with the mandatory provision of Sec. 145.0410 of the URM Ordinance?
5. When checking for the out-of-plane wall anchorage to flexible diaphragms, per the requirements of 97 UBC, Sec. 1633.2.8.1, what values for Rp and a? should be used?
6. Is it required for the roof or floor diaphragm supporting URM walls to have continuous ties or struts between diaphragm chords to distribute the anchorage force specified in 97 UBC, Sec. 1633.2.8, in order to comply with the mandatory provision of Sec. 145.0410 of the URM Ordinance?
7. When submitting plans for compliance with the mandatory provisions of the URM Ordinance, how much information is necessary to be shown for roof / floor framing plans?
8. The URM building under consideration has been previously retrofitted sometime in (1940’s, 1950’s, 1960’s, 1970’s, 1980’s and 1990’s) and as existing has parapet bracing and roof- / floor-to wall anchors. What needs to be submitted to prove compliance with the URM Ordinance?
9. Is Structural Observations required to be provided for URM seismic retrofit work?
10. Is PREQUALIFICATION load testing for anchors required?
11. Is CONFIRMATORY load testing for anchors (In-Place Field Verification of Anchor Installation) required?
12. What is the procedure that shall be used to establish wall anchor design capacities when published allowable capacities are not provided for in the 1997 UCBC or in a nationally recognized research or approval report?
13. What are the applicable regulations for the seismic retrofit of a qualified historical building?
14. Are plans for seismic retrofit of URM buildings registered on local, State or Federal registry as a historical building, subject to review by City’s Historical Resources Board?
15. Are through-bolt anchoring systems acceptable for the seismic retrofit of URM historical buildings?
16. Are components and building materials proposed as a part of a seismic upgrade to a URM building subject to review by The Environmental Review section in the Land Development Review Division of Development Services even if they are not registered as a historical building on local, State or Federal registry?
17. The URM building which I am investigating has no parapets / or has shallow parapets, and therefore does not require parapet bracing. Is it still required to provide roof-to-wall ties?
18. The URM bearing wall supports roof / floor superimposed loads of less than 100 plf. Is this wall considered to be a URM bearing wall?
19. What tributary wall area shall be considered in determination of the roof-to-wall anchorage force to satisfy the Mandatory Provisions of the URM Ordinance?

1. What is required to be done by the URM Ordinance?

The mandatory provisions of the ordinance have three elements which are required to be performed by January 1, 2006. These requirements are 1) Bracing of parapets around building perimeter, AND 2) Roof-to-Wall Ties/anchors around the building perimeter, AND 3) Removal or stabilization of any and all exterior building features which are falling hazards such as exterior stairways, balconies, marquees, cornices, statutes, etc. [SDMC, Sec. 145.0410].

2. In addition to the mandatory provisions, are there any other requirements?

The Ordinance has three triggering provisions, which apply to any URM building, even if the building has been retrofitted per the mandatory provisions. These provisions apply when; 1) the cumulative value of remodel or renovation exceed 100 percent of the value of the building within any 5-year period after January 1, 2001, [SDMC, sec. 145.0407], or 2) the use or occupancy classification of part or all of a building is changed to a use or occupancy classification at a higher relative hazard category, [SDMC, Sec. 145.0408] or 3) the cumulative value of remodel or renovation exceed 50 percent of the value of the building within any 5-year period after January 1, 2001, [SDMC, Sec. 145.0411]. In the case of either provisions 1) or 2) above, the URM building must meet the requirements of Technical Policy B-34-1 “URM Building Plan Review Policy” or the State Historical Building Code for buildings registered on the local, State or Federal registry. In the case of provision 3) above, only floor-to-wall ties/anchors must be provided around the perimeter of the entire building.

3. Is it required to verify the capacity of the entire roof or floor diaphragm in order to comply with the mandatory provisions of Sec. 145.0410 of the URM Ordinance?

No. Verification of the capacity of the entire roof or floor diaphragm, and thus determining the need for retrofitting the roof or floor diaphragm is beyond the scope of Section 145.0410 of the URM Ordinance. Roof- / floor-to-wall anchors must be designed and detailed to resist a minimum force, as set forth by 97 UCBC, Sec. A113.1.3. The roof / floor diaphragm must be checked to show that it is capable of resisting this force at each roof-/floor-to-wall anchor.

4. Is it required to verify the capacity of the entire roof or floor diaphragm shear transfer in order to comply with the mandatory provision of Sec. 145.0410 of the URM Ordinance?

No. verification of the shear transfer capacity of the roof or floor diaphragm at existing URM walls is beyond the scope of Section 145.0410 of the URM Ordinance, thus is not required.

5. When checking for the out-of-plane wall anchorage to flexible diaphragms, per the requirements of 97 UBC, Sec. 1633.2.8.1, what values for Rp and ap should be used?

Rp for anchorages shall equal:

• 1.5 - for shallow expansion anchor bolts, shallow chemical anchors or shallow cast-in-place anchors. Shallow anchors are those with an embedment length-to-diameter ratio of less than 8.
• 1.0 - for anchorages constructed of nonductile materials, or by use of adhesive. [97 UBC, Sec. 1632.2].
• 3.0 - for anchorages with ductile material.

• ap for anchorages shall equal:
  • 1.5 for anchorages with ductile or non-ductile material.
    • Anchors with Ductile material: Expansion anchors, Through bolts.
    • Anchors with Non-Ductile material: Embedded chemical/adhesive/epoxy anchors.

6. Is it required for the roof or floor diaphragm supporting URM walls to have continuous ties or struts between diaphragm chords to distribute the anchorage force specified in 97 UBC, Sec. 1633.2.8, in order to comply with the mandatory provision of Sec. 145.0410 of the URM Ordinance?

No. This requirement is beyond the scope of Section 145.0410 of the URM Ordinance, thus is not required.

7. When submitting plans for compliance with the mandatory provisions of the URM Ordinance, how much information is necessary to be shown for roof / floor framing plans?

Framing information needs to be shown to the extent that is necessary to reference specific roof-/floor-to-wall anchorage connection details.

8. The URM building under consideration has been previously retrofitted sometime in (1940’s, 1950’s, 1960’s, 1970’s, 1980’s and 1990’s) and as existing has parapet bracing and roof- / floor-to wall anchors. What needs to be submitted to prove compliance with the URM Ordinance?

Plans, structural calculations and other evidence must be submitted to demonstrate that for the seismic retrofit work completed, 1) minimum requirements of the current URM Ordinance are satisfied and, 2) a construction permit was issued by the City of San Diego and, 3) final inspection passed by City of San Diego building inspector.

9. Is Structural Observations required to be provided for URM seismic retrofit work?

Yes. Section A105.4 of the 1997 UCBC requires that Structural observations be performed. The observations shall be in accordance with the requirements of 2001 CBC, Sec. 1702.

10. Is PREQUALIFICATION load testing for anchors required?

Yes, when it is desired to use tension or shear capacities for anchors that are larger than those permitted by Table A-1-E of Uniform Code for Building Conservation (UCBC), or where either the wall or anchor types proposed are not provided in the table. Tension anchors whose capacity is published under item 4.2 of the table require testing as referenced in footnote 7. The prequalification load testing procedure and allowable load determination shall be in accordance with the provisions of UBC Standard 21-7, Section 21.704. A minimum factor of safety of 5 shall be used for direct tension tests.

This prequalification load testing report, although preferred to be submitted with the construction seismic retrofit plans and calculations, it may be submitted for review and approval after a building permit has been issued for the proposed seismic retrofit work but, prior to the commencement of construction.

The testing must be performed by construction materials testing laboratories approved by the City of San Diego. For a list of City’s approved testing laboratories, list of Building Newsletters, see special inspection and structural observation requirements.

11. Is CONFIRMATORY load testing for anchors (In-Place Field Verification of Anchor Installation) required?

New Embedded Bolts: Yes. Direct-tension test and calibrated torque wrench test are required to verify the quality of the installation. [97 UCBC, Sec. A107.4, and UBC Std. 21-7, Secs. 21.702 & 21.703]. A minimum factor of safety of 2.5 shall be used for direct tension tests.

New Through Bolts: need not be tested. [97 UCBC, Sec. A107.4]

12. What is the procedure that shall be used to establish wall anchor design capacities when published allowable capacities are not provided for in the 1997 UCBC or in a nationally recognized research or approval report?

A comprehensive testing program must be developed by the structural engineer of record and submitted to the URM Program coordinator at the Division of Building and Safety- Inspection Services section for review and approval. Building Newsletter (BNL) 17-10 may be used as a guideline to draft the testing program. The test program shall be developed based on the “Acceptance Criteria for Anchors in Unreinforced Masonry Elements AC -60” published by ICC Evaluation Services and shall at a minimum include procedures for prequalification load testing and confirmatory load testing as well as in place mortar shear testing. Special inspection shall be provided. Structural Observation performed by the engineer of record shall also be provided.

13. What are the applicable regulations for the seismic retrofit of a qualified historical building?

The seismic retrofit of a qualified historical building shall be designed per SDMC Section 145.0410 (e). The State Historical Building Code shall be used for the force and scoping requirements, and Appendix Chapter 1 of the 1997 UCBC shall be used as a basis of the design.

14. Are plans for seismic retrofit of URM buildings registered on local, State or Federal registry as a historical building, subject to review by City’s Historical Resources Board?

Yes.

15. Are through-bolt anchoring systems acceptable for the seismic retrofit of URM historical buildings?

Use of through-bolt anchoring system with metal plates and nuts has been viewed by the Environmental Review section in the Land Development Review Division of Development Services as a form of alteration, revision or modification of exterior elevations. Although may be an acceptable solution from the engineering and building code considerations, the Historical Resources Board will make the final decision as to whether such anchoring system is considered to be significant alteration/revision/modification of exterior elevations, and whether allowed as an acceptable anchorage method.

16. Are components and building materials proposed as a part of a seismic upgrade to a URM building subject to review by The Environmental Review section in the Land Development Review Division of Development Services even if they are not registered as a historical building on local, State or Federal registry?

Whether or not plans for seismic retrofit of a URM building will be required to be reviewed by the City’s Environmental Review section, will depend on whether or not the exterior façade and/or exterior elevations of the building, is visible to the general public, is proposed to be altered, revised and/or modified in any shape or form.

Use of thru-bolt anchoring system with metal plate and nut has been viewed as a form of alteration, revision or modification of exterior elevations. The Environmental Review section will make the final determination as to whether such anchoring system is considered to be significant alteration/revision/modification of exterior elevations, and whether allowed as an acceptable anchorage method.

17. The URM building which I am investigating has no parapets / or has shallow parapets, and therefore does not require parapet bracing. Is it still required to provide roof-to-wall ties?

Yes. The requirements for parapet bracing and for roof-to-wall ties are two separate and independent requirements. If the parapets of a URM building need not be braced, or if a URM building does not have any parapets, roof diaphragm and URM walls must be tied together around the perimeter of the entire building. [SDMC, Sec. 145.0410(d)].

18. The URM bearing wall supports roof / floor superimposed loads of less than 100 plf. Is this wall considered to be a URM bearing wall?

No. Section 145.0404 defines an unreinforced masonry bearing wall as one that satisfied the adopted definition in the 1991 Edition of the Uniform Code for Building Conservation (UCBC) Appendix Chapter 1. Section A103 of the 1991 UCBC defines an unreinforced masonry bearing wall as a “URM wall which provides the vertical support for a floor or roof for which the total superimposed load exceeds 100 pounds per lineal foot of wall.”

19. What tributary wall area shall be considered in determination of the roof-to-wall anchorage force to satisfy the Mandatory Provisions of the URM Ordinance?

1) For multi-story buildings: The tributary wall area for anchorage at the roof level may be calculated as if the floors were anchored. Cantilever action of the roof parapet shall always be considered.

2) For single-story buildings: The tributary wall area for anchorage at the roof level may be calculated as if the wall was anchored at its base. Cantilever action of the roof parapet shall always be considered.