Is the House You Are Buying Quake Safe?

The Northridge earthquake showed how important it is for your house to be solidly built.

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Before you invest your life’s savings in a home, you should review its structural soundness, making sure that it is able to withstand both sudden and gradual stresses placed upon it.

By conducting a visual inspection or discussing the construction of the house with your builder, you can help safeguard your huge financial and emotional investment.

Depending on the level of thoroughness you desire, you may use some or all of the suggestions that follow.

If your new house is under construction, you can conduct periodic inspections as it is being built. If you are buying a finished home, many of the suggestions can be done easily, but you will need to break off small pieces of plaster to inspect any hidden items in the house.

In a nutshell, your house should be built like a crate box. A crate box endures being stuffed with goods, tossed around from site to site and carted thousands of miles, because it is designed to absorb the stress and pressure placed upon it. Your house should be designed likewise.

Begin your inspection in the attic, by examining the underside of the roof. If it is sagging, you can expect water to get trapped and the roof will eventually leak and sometimes fall. The roof’s underlay should be made of plywood or wood boards. Look around the attic to make sure that the roof’s supporting framework, called “trusses” by home builders, is not damaged and is built in the shape of closed triangles.

Take a good look at the fasteners that hold the boards together. Only nails, bolts and wood-lag screws should generally be used, sometimes along with metal straps or clips. The nails should be long and large enough in diameter to hold the wood together. The frame of the walls should be 2-by-4s if the house is one or two stories and 2-by-6s if it is three stories tall.

When buying a home in California, the most important item to check, or to discuss with the builder in the construction of a new home, is that some of the walls have been built to withstand an earthquake.

Called “shear walls” by builders, these walls are built to protect your house against the bidirectional stress of an earthquake. While seismic forces pull a house in one direction and then back in the other direction, these walls keep the house anchored to its foundation and distribute the stress of an earthquake evenly throughout the house.

Shear walls must be well-fastened to the foundation and the roof or floors, and must not have any windows and doors. On the exterior of the house, shear walls are usually built with plywood. They should be secured to the foundation with hold-down clips and bolts at the ends of the walls, especially if the walls are short, and to the floors or roofs with nails. Nails should appear along the four sides of the shear wall’s edges and across its center.

Plasterboard on interior and exterior shear walls should be nailed, not screwed. If the house is already finished, you will need to break some plaster to check for evidence of hold-down clips, bolts and proper nailing, because they are out of sight behind the wall’s interior gypsum covering or exterior stucco and plywood.

Bear in mind that breaking plaster may not be desirable for everyone, but is an option for some after opening escrow. You can hire a plaster contractor for a nominal fee to fix the damage. The repair charge is small when viewed in the context of the cost of the Southern California home.

If the house is under construction, conduct your own visual inspection.

For older homes, especially ones built before World War II, you should make sure that the house has been anchored to its foundation. To confirm this, go to the sides of the house and look for a crawl space opening. Enter this crawl space and check for anchor bolts that connect the house walls to the concrete foundation.

If you do not find any anchor bolting and still wish to buy the house, you should hire a local concrete-anchor-bolting company shortly after moving in to your new home. The company should install concrete-expansion anchors, if possible, because they will allow the bolting to handle the stress of an earthquake. Do not accept a sheet metal clip in lieu of an anchor bolt.

Look at the top of each story’s frame for two rows of 2-by-4s or 2-by-6s, called “top plates” by home builders, placed one on top of the other in a staggered manner. To prevent pipes from interrupting the stresses in the frame’s beams, a steel plate should be mounted on the side of the 2-by-4s or 2-by-6s where the pipes are located.

The last item to inspect inside the house is the floor. It should be made of plywood or decking, but not pressboard. The floor’s beams, or “joists” in building parlance, should be sufficient to support the length of the span.

Outside the house, check the foundation for excessive cracking. Look for uneven settlement of the foundation, especially if the house is built on clay soil. Another way to check for undesired settlement is to look above windows and doors for any bend in the beams and lintels and for any difficulty in opening and closing windows and doors.

Inspect soil conditions. It should be compact and firm. Also, look for a proper drainage system to divert rain away.

If the house is located on a hill, note the integrity of the retaining wall. Is it cracking or settling? If so, there could be a problem. Also, make certain there is a proper drainage system behind the retaining wall.

You also should inspect the condition of stucco and plasterboard. Only minimal cracking is acceptable. Keep in mind when checking for cracks that a slanted single crack indicates settlement or shrinkage of the plaster, while a crack in the shape of an “X” indicates that an earthquake damaged the plaster and wall. If a wall has an X-shaped crack, the house’s ability to withstand the next major seismic force is much less.

Last, scan or ask about the materials used in the house. The concrete should be high quality; again, cracks may indicate trouble. Douglas fir should be the wood of choice in California, when possible.

Most California homes are structurally acceptable. But be on the look out for the ones that are cracking at the seams.