What Is a URM Building? Understanding Unreinforced Masonry

Written by Saunders Seismic on 21st July 2025

Unreinforced masonry (URM) buildings are among the most vulnerable structures in an earthquake. Many were built before modern seismic codes existed, and their brittle construction makes them prone to severe damage or collapse during ground shaking.

In the 1994 Northridge earthquake, dozens of URM buildings in Southern California suffered partial or total collapse. Many had been identified as high-risk but hadn’t yet been retrofitted. The damage was so severe that several cities enacted mandatory retrofit ordinances in the years that followed.

If your building was constructed before modern seismic codes, it may contain unreinforced masonry—and that could put both lives and investments at risk. In this article, we’ll explain what URM is, how to identify it, and what reinforcement options are available.

What Is Unreinforced Masonry?

Unreinforced masonry refers to brick, block, or stone construction that, most of the time, lacks internal steel reinforcement. These buildings rely solely on the compressive strength of the masonry—but lack the structural flexibility needed to withstand side-to-side forces like those caused by an earthquake.

If your building was constructed before the 1940s or 1950s (depending on your location), there’s a good chance it contains unreinforced masonry. In some areas, buildings from the 1960s, 1970s or later may also include URM elements due to delayed code updates or construction practices at the time.

Reinforced vs. Unreinforced Masonry: What’s the Difference?

The biggest difference is what’s hidden inside the walls.

Reinforced masonry includes steel bars (rebar) embedded in the walls and tied into the floors and roof. It’s designed to resist both vertical and lateral forces.
Unreinforced masonry has no internal steel—making it strong in compression but extremely weak under lateral stress, such as seismic shaking.

In an earthquake, unreinforced masonry walls are at risk of cracking, separating from the roof, or collapsing altogether.

How Do You Know if Masonry Is Reinforced or Not?

It’s not always easy to tell by looking, but here are a few indicators that your building might be unreinforced:

It was built before the 1940s (or before local seismic codes were adopted).
The walls are made of exposed brick or block with no visible reinforcement or anchoring plates.
There’s no evidence of anchorage between the walls and the roof or floor system.
The building appears on a city or county URM inventory (many jurisdictions keep lists of known URM structures).

Ultimately, the only way to be sure is to have the building professionally evaluated. Saunders Seismic works closely with experienced structural engineers who specialize in retrofit assessments for commercial and industrial URM buildings.

How to Reinforce a URM Building

Strengthening a URM building for seismic safety typically involves a combination of the following strategies:

Wall anchorage: Secure masonry walls to the floor(s) and roof to keep them from separating during seismic shaking.
Out-of-plane wall bracing: Add horizontal bracing to prevent the walls from bowing or falling outward, reducing the risk of “pancaking” during lateral movement.
Diaphragm strengthening and continuity ties: Reinforce floors and roofs—typically with plywood or structural sheathing—and install continuity ties to help the entire structure move as a unity and distribute seismic forces more effectively.
Shear walls or steel frames: Add structural elements that resist horizontal movement and increase overall building stability.

The right retrofit solution depends on your building’s age, use, condition, and location. However, the goal is always the same: to improve life safety, minimize disruption, and support business continuity while meeting performance objectives like SEL/SUL.

Real-World Challenges with URM Retrofits

URM buildings rarely follow a standard design—and that’s exactly what makes them so challenging to retrofit.

At Saunders Seismic, we’ve seen it all: open storefronts needing custom moment frames, deteriorated trusses, unanchored walls, and aging materials. Even the direction of the roof sheathing (like 1×6 boards) can determine whether existing roofing can be preserved or must be removed entirely.

In many cases, a true retrofit goes far beyond basic wall anchorage and may require:

Constructing new interior walls to bear seismic loads
Repairing or replacing deteriorated roof framing
Installing new roof sheathing to improve diaphragm performance

The reality is that bringing a URM building up to current seismic standards is often a significant investment. Depending on the condition and complexity, costs can range from $6 to over $30 per square foot. And without a detailed structural design, accurate budgeting is nearly impossible.

That’s why we strongly recommend starting with a professional assessment. Understanding what you’re working with is the first and most important step toward making informed, cost-effective retrofit decisions.

URM buildings are often less expensive to purchase—and for good reason. Without retrofit, they carry significant seismic risk and bringing them up to standard can require a substantial investment.

Before you buy, get a full assessment to avoid surprises. In many cases, it may be more cost-effective to consider a building type that already meets current codes.

Thinking of buying a URM building?

Here’s what we tell our clients:

Unless you’re ready for a retrofit, it might not be the right building for you.

Why It’s Not Just About Collapse: Other URM Risks

Even if your building never experiences a major earthquake, owning an unreinforced masonry structure can affect:

Insurance coverage: Many insurers refuse to cover URM buildings or require proof of seismic retrofitting.
Financing and resale: Lenders may flag URM buildings as high-risk, complicating refinancing or sale.
Local compliance: Cities like Los Angeles, San Francisco, and Pasadena already require retrofitting for URM structures—and more jurisdictions are following suit.

If you wait until you’re required to retrofit, you may end up facing higher costs, tighter timelines, and more disruption.

A Tragic Early Example: Mission San Juan Capistrano, 1812

Unreinforced masonry has been vulnerable to earthquakes long before modern building codes existed. One of California’s earliest and most tragic examples occurred in 1812, when an estimated 7.5 magnitude earthquake along the San Andreas Fault shook Southern California

One of the most devastating impacts was the collapse of the Great Stone Church at Mission San Juan Capistrano—a structure completed just six years earlier.

Forty parishioners were killed during early morning Mass. The church had thick stone walls, but like other structures of its time, it was built without any internal reinforcement or knowledge of seismic design.

The church was never rebuilt. Its ruins remain today as a powerful reminder of California’s seismic history—and the risks of unreinforced construction.

How Earthquakes Changed California URM Policies

While the 1812 San Juan Capistrano collapse was an early warning, it took modern, high-profile earthquakes to drive real policy change and retrofitting efforts across California.

Earthquake	Year	URM Impact
San Fernando (Sylmar)	1971	Prompted California’s first URM ordinances by exposing widespread parapet and wall failures.
Loma Prieta (Bay Area)	1989	Accelerated local retrofit mandates in San Francisco and Santa Cruz after widespread URM collapses.
Northridge (Los Angeles)	1994	Strengthened enforcement of existing URM laws and led to new retrofit requirements.
San Simeon (Paso Robles)	2003	Increased local inspections and tracking efforts after URM debris caused two fatalities.

Don’t Wait for the Next Earthquake to Expose a Weakness

Unreinforced masonry buildings are a known risk—and in many regions, building departments have begun mandating retrofits. But even if it’s not required in your area, addressing the issue now can prevent far greater costs later.

At Saunders Seismic, we’ve helped commercial and industrial clients across the western U.S. strengthen their URM buildings with cost-conscious, effective retrofits.

We provide honest answers, realistic budgets, and clear guidance throughout the process—so you can move forward with confidence.