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Brick foundation prone to fail in major quake

September 10th, 2008 8:32 PM by Ron Mastrodonato

Brick foundation prone to fail in major quake
Why replacing with reinforced concrete is worth the cost

September 10, 2008

By Bill and Kevin Burnett
Inman News

Q: My two-story, Berkeley, Calif., home, built in 1905, is very close to the Hayward Fault. It is lath and plaster with a stucco exterior. The house is U-shaped around a courtyard. There is only one area -- about 20 feet by 10 feet -- under the house that you could call a basement. The rest is crawlspace.

The foundation is mostly brick except for the 10-by-20-foot section of the house where the space between the earth and the floor joists is tall enough to stand in. In this area the foundation is concrete, which, I think, was poured over brick. In this area the mudsill is bolted to the foundation but nowhere else. A few years ago I had a plywood shear wall installed in this section. The footprint of the house is just under 2,000 square feet. There are cracks visible on the outside where the house meets the foundation.

What do you think I should do to be safer and to protect the value of my house? Could you also provide a ballpark estimate of costs for the answer?

A: We can only imagine the jewel you have -- classic details such as quarter-sawn oak floors, natural wood wainscoting, plate rails, coved ceilings and built-in hutches. The courtyard sounds charming, the perfect place for a cup of afternoon tea (or a beer) on a summer day. Preservation and protection of this asset should be the order of the day.

The brick foundation offers little, if any, protection in the event the Hayward Fault slips. It should be replaced with a modern reinforced concrete foundation. We'd also suggest you investigate going at least one step further and shear-panel the cripple walls.

The cost of replacing the brick foundation will be dear, but it will provide the protection you need. In our view, the money would be well spent.

During a major quake, two very bad things can happen to houses that rest on a brick foundation. First, the lateral forces of the quake can cause the house to slide off the foundation. The other is that those same lateral forces can cause the cripple walls to buckle, collapsing the house. The horizontal cracks you mention along the foundation line may be the result of the lateral movement of previous quakes. They may also be the result of the bricks settling.

Around the turn of the 20th century, brick foundations were common. Homes were constructed on what were essentially wide brick-and-mortar walls dug into the ground. Over time, moisture caused the mortar to fail. At best, mudsills were mortared in place. There were no mechanical fasteners to secure the mudsill to the foundation.

We suspect that on a close inspection of your foundation you'll find sand where solid mortar used to be.

Modern foundations are made of reinforced concrete. They take the form of an inverted "T" with the base of the "T" called the footing. The footing provides a wide base to accept the forces from the walls and roof above. The taller the building, the wider the footing.

The Uniform Building Code provides the minimum specifications for footing widths for buildings of various heights. Resting on the footing is the stem wall. The purpose of the stem wall is to raise the height of the foundation above the exterior grade to keep the wood members out of the dirt.

Mudsills are bolted to the foundation using J-bolts (named for their shape), which are placed no more than 6 feet apart and 1 foot from every corner. Steel reinforcing bar "rebar" is placed in the wet concrete to increase the tensile strength of the foundation. Rebar helps prevent the concrete from developing vertical cracks.

The portion of your foundation that appears to be concrete is probably a "cap and saddle." In this process, the brick foundation is encased with concrete. Rebar is added for rigidity and the mudsill is secured by J-bolts imbedded in the concrete cap. Although it provides a bit more structural support, the core of the foundation is still old brick and should be replaced.

The process for replacing a brick foundation with a reinforced concrete foundation is conceptually simple. The first step is to construct a temporary wall close to the perimeter of the house to support the structure. Next, remove the bricks. Finally form and pour the new foundation. It's a good time to replace the 100-plus-year-old mudsill with a new pressure-treated version the same width as the cripple studs. It will allow a flat surface to attach the shear panels to the cripple wall. The job can be done in stages or all at once. Although when we were younger we replaced a couple of foundations ourselves, these days we'd leave the job to the professionals.

The cost will probably be in the tens of thousands of dollars -- figure a minimum of $200 per foot. To find the perfect contractor, we can suggest a couple of avenues to pursue.

First, because you have a historic home, contact one of the preservation societies in the area for references. We suggest the Alameda Architectural Preservation Society (formerly the Alameda Victorian Preservation Society). The members of these organizations are involved in the renovation of their own homes and generally have a line on contractors who do good work at a fair price.

Our other suggestion is that you try to locate a contractor/engineer who specializes in earthquake retrofits. Local building departments can help with references. Try Berkeley and San Leandro. These contractors may charge for an estimate. If they do, expect a detailed report with the scope of the proposed work outlined as well as a cost estimate. Ask for a sample proposal before agreeing to pay for the estimate.


Posted in:General
Posted by Ron Mastrodonato on September 10th, 2008 8:32 PM


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