TL;DR (generated, confidence: high)

BCG 23-11 provides an alternate method for seismic retrofits of unreinforced masonry buildings that simplifies design by allowing new vertical elements to resist 100% of seismic loads, thereby classifying URM walls as non-structural components. The method applies to Risk Categories I-III under ASCE 41 BPOE or BPON standards, but is excluded for Risk Category IV structures.

Key points:

Alternate method bypasses complex ASCE 41 compatibility analysis by requiring new vertical elements to be designed for 100% of seismic loads (Building Code Guide 23-11: URM Seismic Retrofits ↗)
When using the alternate method, URM walls are classified as 'nonstructural components', exempting them from adequacy demonstration and deformation compatibility analysis (Building Code Guide 23-11: URM Seismic Retrofits ↗)
Applicable only to Risk Categories I, II, and III buildings under ASCE 41 BPOE or BPON seismic improvement standards (Building Code Guide 23-11: URM Seismic Retrofits ↗)
NOT applicable to Risk Category IV structures, which must demonstrate deformation compatibility per ASCE 41-17 Section 7.2.3.3 (Building Code Guide 23-11: URM Seismic Retrofits ↗)
Exception: existing URM walls in good condition with flexible diaphragms per ASCE 41 may be used as primary structural elements and must meet full deformation compatibility requirements (Building Code Guide 23-11: URM Seismic Retrofits ↗)
The alternate method applies only to vertical element and URM wall compatibility; all other ASCE 41 requirements remain mandatory (Building Code Guide 23-11: URM Seismic Retrofits ↗)

Building Code Guide 23-11: URM Seismic Retrofits

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Source: Building Code Guide 23-11: URM Seismic Retrofits ↗ Last modified: Sun, 19 Apr 2026 20:06:32 GMT

Building Code Guides (BCGs) and Building Official Determinations (BODs) provide answers about the application of building codes and outline optional alternates. BODs are typically smaller in scope and address simpler questions. Code Guides provide a comprehensive alternative to a complicated set of code requirements.

BCG 23-11: URM Seismic Retrofits

QUESTION: ASCE 41 and structural design standard of practice requires complex analysis and demonstration of compatibility between new lateral elements and existing masonry components during the seismic upgrade of a URM building. As these requirements are disproportionately burdensome, is there an alternate method to demonstrate compatibility?

RESPONSE: Design professionals may follow the requirements of the Alternate Method outlined in this document; provided the structures are within the scope limitations of this document.

I. Introduction

Where new vertical elements are being added to resist lateral forces as part of seismic upgrade of a URM building, analysis requirements of ASCE 41 and structural design standard of practice requires distribution of lateral forces along a wall line of resistance, in proportion to the relative rigidities. The level of complexity required to demonstrate this compatibility between new lateral elements and existing masonry components is very burdensome and not proportionate to the level of analysis required on most projects. Moreover, uncertainties in accurately modelling the properties of these archaic URM components often lead to analysis with low level of confidence and questionable results.

Therefore, in lieu of demonstration of compatibility between the URM components and new vertical elements of the Seismic Force Resisting System, it is acceptable for a design professional to follow the requirements of the Alternate Method outlined in this document; provided the structures are within the scope limitations of this document. When all the requirements of this document are provided for, it is not required to demonstrate the adequacy of the masonry components along the line of seismic force resistance under consideration, and equivalency to the deformation compatibility requirements of ASCE 41 are deemed satisfied. By using the Alternate Method, the URM walls will be classified as “Non-structural” components as defined in ASCE41 (Nonstructural component: element of a building that are not intended as part of the lateral or the gravity system, and still may pose seismic hazard due to seismic accelerations or induced displacements).

II. Scope

The Alternate method presented in this document is applicable to buildings:
1. In Risk Category I, II and III when the seismic improvement standard is either ASCE 41 BPOE or BPON.
2. Where new vertical elements of the Seismic Force Resisting system are provided and these new elements are designed to take 100% of the required seismic loads.
  
  Exception: if the existing URM walls are in good condition, and the diaphragm meets ASCE41 criteria as flexible, then such walls may be used to resist lateral loads and shall be analyzed as Primary Elements and meet all requirements of ASCE 41 including deformation compatibility requirements.
The Alternate method is NOT applicable for structures in Risk Category IV structures. Deformation compatibility must be demonstrated per ASCE 41-17 §7.2.3.3.
This Alternate method applies only as an alternate to provisions of ASCE 41 that relate to compatibility of new vertical elements of the lateral system and existing URM walls. All other applicable requirements of ASCE 41 or other standards apply as required by those standards.