shoring up basement foundation with plywood

Old 12-02-02, 11:56 AM
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shoring up basement foundation with plywood

I live in a 1891 victorian duplex in San Francisco. about 60% of the home adjoins the properties on either side.

I'm looking at doing some simple repairs to shore up the foundation.

My foundation is about 30% uncapped brick, the other 70% is capped brick. Parts of the uncapped brick mortar are crumbling a bit , and need some repointing. I assume this is a pretty easy thing to do, just clean it out, and slap some new mortar in there, right? I also have heard that its really good for the structural integrety to attach plywood (what width?) between the studs in the basement- just like putting sheetrock on studs in living space.

Does anyone have any tips on either of these projects? or about shoring up the foundation in general. The house hasnt settled much, seems very solid, is built on a rocky area, and has withstood 2 major quakes, so I feel good about it. I just want to make sure the foundation is ready for the next few decades.

Old 12-02-02, 09:11 PM
bungalow jeff
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Make sure you use the correct mortar mix with the old brick. New cement mortars are too hard and will cause damage to the brick. Old brick requires a higher lime to cement ratio mortar.
Old 12-08-02, 05:30 AM
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The load of the house sits on the foundation. If you have framed walls in the basement, then the only walls carrying any load would be interior walls where there is no foundation. Therefore, any other walls are non-loadbearing. Non loadbearing walls, including the exterior walls framed next to the foundation, don't need plywood for structural integrity. Is there another reason you might want to do the plywood?
Old 12-08-02, 09:12 AM
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Seismic upgrades must meet codes


Mercury News Real Estate Writer

The 70-year old Los Altos Hills home easily passed muster for an Allstate quake insurance policy after the agent inspected the home's code-complying seismic upgrades. That reassured new owner Carol Crites, who had purchased the home partly because the $4,000 worth of upgrades protect the house against major damage from all but the worst earthquakes. But there was also a nice bonus for Crites: That protection could also save them as much as $250,000 - based on the 25 percent deductible on the quake-insurance policy she purchased for the million-dollar home.

"If the work wasn't done, we would have negotiated for the seller to pay for it as part of the sales contract. It would be terrible to lose such an asset," Crites said.

You can pay for seismic retrofitting now or you can pay for it later, but, chances are, you will pay. Its primary purpose is to protect life and property. But residential seismic retrofitting on certain homes has become even more of a necessity for owners who want to obtain a new quake policy or renew an old one. Massive claim payouts from the 1989 Loma Prieta quake and more recently from last year's Northridge quake have forced most insurers to severely curtail their homeowners insurance business.

That's because, in California, insurers who offer homeowners insurance policies must also offer quake insurance. To reduce the risk of earthquake related payouts, virtually all insurers consider a home's seismic safety before writing policies. But even with coverage, deductible payments as high as 25 percent can be catastrophic.

"Rather than focus on ways to pay enormous repair bills, a cheaper and more efficient approach is to lessen the risk of catastrophic damage in the first place," says Sydney Adams, a spokeswoman with the non-profit Building Education Center in Berkeley.

Selling point
Seismic upgrades also become part of negotiations during a home sale. While the seller isn't required to perform seismic upgrades, the law requires him or her to disclose known facts about the home's seismic safety. If a seller honestly isn't aware of seismic safety construction, most buyers today hire an inspector to check out the home's susceptibility to quake damage.

"I've closed some escrows that were pretty horrendous. You don't need a kick in the head like just when you are going to close escrow." says Dolores Shaw, a Coldwell Banker-Fox, Los Altos listing agent on the Crites home.

Homes most likely in need of upgrades are those built before the late 1940's. After World War II, new building codes required that homes be bolted to their foundations. Approximately 66,000 houses in Santa Clara County were built before 1940, according to U.S. Census figures.

Stronger Foundation
What kind of retrofitting work can you expect? The idea is to strengthen foundation connections to create one unified structure to better withstand the various forces of an earthquake. The work can cost less than $5,000. The primary seismic safety measure requires bolting the mudsill to the foundation. That helps inhibit a quake's lifting forces, energy that can throw the structure off its foundation. Where you can't access areas to bolt the foundation, such as on slab foundation homes, foundation brackets can be nailed to the mudsill and then bolted to the side of the foundation.

For some slab foundation homes, heavy steel brackets, called hold-downs, can also be used to secure the ends of the walls by bolting wall end studs to the foundation. Bolting may not be enough however, if your home is weak in other areas, says Forrest Linebarger, president of the non-profit Contractors Organization for Professional Standards in Mountain View. Also, the disclosure statement requires information additional to that about foundation bolting. What's found in the disclosure statement could lead some buyers to negotiate for more work.

Some older homes have "pony" walls between the first floor and the foundation. The unsupported wall generally surrounds a large crawl space, basement or garage and needs to be reinforced with shear walls - plywood installed on the inside of the existing pony wall. The construction protects the home against an earthquake's lateral forces, which can cause the wall to buckle and fold over off its foundation.

You may also need to either attach the first floor to the foundation or to the pony wall. To attach it to the foundation, a foundation joist anchor is used to connect the floor joists to the foundation. Otherwise, fasten metal reinforcing angles to the shear-wall top plate and the first-floor rim joist. Still more lateral protection comes from triangular gussets or metal T-straps that connect the floor girders to the posts.

"Properly designed and constructed, a one or two-story, wood-frame, single-family home is one of the safest structures during an earthquake," says Andrew A. Adelman, San Jose's chief building official.

Reprinted from the San Jose Mercury News
Retrieved 08 December 2002

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