Protecting your property from earthquakes
Earthquake protection can involve a variety of changes to your house andproperty -- changes that can vary in complexity and cost. One example of earthquake protection isanchoring large pieces of furniture, such as bookcases and file cabinets, sothat they will remain upright during an earthquake. This is something that manyhomeowners can probably do on their own.
If you aren'tsure whether your house is at risk from earthquakes, check with your localbuilding official, city engineer, or planning and zoning administrator. They cantell you whether you are in an earthquake hazard area. Also, they usually cantell you how to protect yourself and your house and property from earthquakes.
You may be able tomake some types of changes yourself. But complicated or large-scale changes andthose that affect the structure of your house or its electrical wiring andplumbing should be carried out only by a professional contractor licensed towork in your state, county, or city.
During an earthquake, large pieces of furniture such as tall bookcases andfile cabinets can fall on you or members of your family. Toppled furniture canalso block exits and prevent you from escaping. Anchoring furniture so that itremains upright not only helps prevent injuries but also helps protect both thefurniture and its contents.
You can anchor large pieces of furniture in several ways. The figure showshow to anchor a bookcase to a wall, but the same methods can be used for otherpieces of furniture. As shown in the figure, a bookcase can be anchored withmetal L brackets and screws along its top or sides (either inside or outside) orwith screws through its back.
Tips -- Keep these points in mind when you anchor large pieces of furniture:
- Make sure that all anchoring screws penetrate not just the wall but the studsbehind it as well. Screws embedded only in drywall or plaster will pull out.Regardless of the anchoring method you use, the screws should be long enough toextend at least 2 inches into the wall and studs.
- Before anchoring a bookcase with screws through its back, make sure the backis sturdy enough and that it is securely attached to the sides, top, and bottom.Some bookcases have backs made of very thin materials that are held in placewith only small screws or staples that can easily pull out. Those bookcasesshould be anchored with brackets.
- If you have two or more bookcases or file cabinets that sit next to eachother, consider connecting them to one another as well as to the wall. They willbe even more stable if you do.
- If possible, move all bookcases, file cabinets, and other large pieces offurniture away from exits so that if they do fall, they won't prevent you fromescaping.
- To prevent the contents of your bookcases from falling out, you can install athin metal or plastic rod, a wood dowel, or even an elastic band across thefront of each shelf.
Estimated cost: The cost of anchoring a bookcase or filecabinet will depend on its width. In general, if you do the work yourself, youcan expect the cost to be approximately $5 per foot. So, for example, anchoringa 3-foot-wide bookcase will cost you about $15. This amount covers only thehardware you will have to buy and excludes the cost of any tools you use and thevalue of your time. If you hire a contractor or handyman to do the work, youwill have to pay for time as well as materials.
Duringan earthquake, framed pictures and mirrors that are not securely attached towalls can easily fall. Large pictures and mirrors can cause injuries when theyfall, and the broken glass that often results increases the potential forinjury.
As shown in the figure, one way to mount framed pictures and mirrors securelyis to use long-shanked, open eye-hooks instead of traditional picture hangers.The eye-hooks must be long enough to penetrate the wall stud as well as thedrywall or plaster. Eye-hooks used in this way are much less likely to pull outof the wall than picture hooks installed with nails that penetrate only thedrywall or plaster. Also, an alternative to running wire across the back of thepicture or mirror is to use closed eye-hooks securely screwed into the back ofthe frame.
Tips: Keep these points in mind when you hang framed pictures ormirrors:
- The number of eye hooks you need for a picture or mirror will depend on its size and weight. Large pictures and mirrors will be more stable when mounted on two hooks rather than one.
- Make sure that eye-hooks penetrate not just the wall but the studs behind it as well. Eye-hooks embedded only in drywall or plaster are likely to pull out. To be embedded deeply enough, eye-hooks should be at least 12 inches long.
- Regardless of whether you use picture wire or closed eye-hooks on the back of the picture or mirror, make sure the hooks, screws, or other types of mounting hardware are securely attached to the frame.
- If possible, don't hang large pictures or mirrors in places where they are more likely to fall on someone, such as over beds, chairs, or couches.
Estimated cost: The cost of mounting a picture or mirror witheye-hooks will depend on its size and weight. In general, for a large picture ormirror that requires two eye-hooks, you can expect the cost to be approximately$3 to $5. This amount covers only the hardware you will have to buy, not anytools you use or the value of your time. If you hire a contractor or handyman todo the work, you will have to pay for time as well as materials.
Duringan earthquake, drawers and cabinet doors can open and the stored materials canspill out and damage floors and floor coverings. Objects that fall from overheadcabinets can injure you or members of your family.
One way to prevent the accidental opening of drawers and cabinet doors is toinstall latches such as barrel bolts, safety hasps, and child-proof locks. Mosthardware and home supply stores stock a variety of latches. The figure shows twotypes child-proof locks, one for drawers and one for cabinet doors. Most typesof permanent latches can be installed easily and will not interfere with openingand closing of drawers and doors. The slide lock shown at right can be used oncabinets that do not need to be opened frequently; it is easily installed andremoved.
Tips -- Keep these points in mind when you install latches on drawersand cabinet doors:
- When possible, do not store heavy, breakable, or dangerous items (such as insecticides, solvents, and bleach) in overhead cabinets.
- Do not rely on magnetic or pinch-grip catches to hold cabinet doors closed, especially on overhead cabinets and any cabinets that contain heavy, breakable, or dangerous items.
- Install latches according to the manufacturer's directions. For example, use all of the hardware provided with the latch and do not substitute undersized screws or bolts for those provided.
Estimated cost: The cost of adding latches will depend on the type youdecide to buy and the number of drawers and cabinet doors you want to secure.Most latches will cost between $2 and $5. So, for example, If you do the workyourself, the cost of adding latches to all the cabinets and drawers in amedium-sized kitchen could range from about $60 to about $100. If you hire acontractor or handyman to install latches, you will have to pay for time as wellas materials.
The tremors caused by even minor earthquakes can easily move personalcomputer systems, stereo systems, television sets, and other small appliancesthat typically sit on desks, tables, and countertops. If they fall, they can bedamaged beyond repair.
As shown in the figure, you can protect desktop computers and other smallappliances by restraining them in a variety of ways. Some methods, such as usinghook-and-loop material (Velcro for example), require no tools. Others, whichinclude using chain, cables, or elastic cord ("bungee" cords forexample), will usually require simple hand tools.
Tips -- Keep these points in mind when you restrain desktop computers and appliances:
- Make sure that the desk or table the appliance sits on is not so light thatit can be easily over-turned. If it is, and you can't move the appliance toanother location, consider anchoring the desk or table to the floor or wall.
- You can anchor the ends of chains, cables, or elastic cords to either thewall or the surface of the desk, table, or counter using eye-hooks, rings,screws and washers, or other types of mounts.
- If you want to use a wall-anchored chain, cable, or cord, attach it to aclosed eye-hook screwed into the wall or to a wall mount (such as a ring orplate) attached with screws.
- Make sure the eye-hook or screws are long enough topenetrate not just the wall but the studs behind it as well.
Estimated cost:Restraining a single desktop computer or appliance with one of the methodsdescribed will cost you about $2 to $10, depending on the amount of hardwarerequired. Using hook-and-loop material will be the cheapest method. Using chainor cable will be the most expensive method but may be necessary for heavy items.
Duringearthquakes, propane tanks can break free of their supporting legs. When a tankfalls, there is always a danger of a fire or an explosion. Even when a tankremains on its legs, its supply line can be ruptured. Escaping gas can thencause a fire. Similar problems can occur with smaller, compressed gas cylinders,which are often stored inside a house or garage.
One way to prevent damage to propane tanks and compressed gas cylinders is toanchor and brace them securely. The figure shows how the legs of a propane tankcan be braced and anchored. Using a flexible connection on the supply line willhelp reduce the likelihood of a leak. Compressed gas cylinders, because theyhave to be periodically replaced, cannot be permanently anchored. But you canuse chains to attach them to a wall so that they will remain upright.
Tips -- Keep these points in mind when you anchor and brace propanetanks or compressed gas cylinders:
- Before you alter your propane tank in any way, make sure that the tank is your property and not rented from the propane supplier.
- Before welding new bracing to the tank legs, you must remove the gas from the tank. You should also check with your propane supplier to find out whether additional precautions are necessary.
- Clear the area around the propane tank to ensure that there are no tall or heavy objects that could fall on the tank or rupture the supply line.
- Keep a wrench near the shutoff valve and make sure the members of your family know how to turn off the supply line if they smell a gas leak. On larger tanks, such as farm tanks, consider installing a seismic shutoff valve that will automatically turn off the gas during an earthquake.
- Provide a flexible connection between the propane tank and the supply line and where the supply line enters the house. But keep in mind that adding a flexible connection to a propane tank line should be done by a licensed contractor, who will ensure that the work is done correctly and according to all applicable codes. This is important for your safety.
- To attach a compressed gas cylinder to a wall, use two lengths of chain around the cylinder -- one just below the top of the cylinder and one just above the bottom. The chains should be attached to eye hooks that are screwed into the wall. In wood-frame walls, the eye hooks must be long enough to penetrate not just the wall but the studs behind it as well. In concrete or masonry block walls, the eye hooks should be installed with expansion anchors or molly bolts.
Estimated cost: Bracing and anchoring a propane tank will cost about$250. Having flexible connections installed on the tank and at the house willcost about $75. Attaching one gas cylinder to the wall will cost about $50.
Becausemost gas and water lines are rigid, they can be torn from their connectionpoints during an earthquake. The results could include not only serious damageto your house but also injury to you and members of your family. A broken gasline is especially serious because of the potential for a fire or even anexplosion.
One way to prevent broken gas and water lines is to have flexible connectionpipes installed between appliances and their supply lines. The figure shows aflexible connection installed on a gas furnace. The same method can be used forother appliances, such as a hot water heater, clothes dryer, or stove. Alicensed contractor can usually do this for you easily.
Tips -- Keep these points in mind when you have flexible connectionsinstalled:
- Changes to the gas lines and plumbing in your house must be done by a licensed contractor, who will ensure that the work is done correctly and according to all applicable codes. This is important for your safety.
- A flexible connection will help protect against a small amount of movement but is not designed to function when the appliance it is connected to moves extensively or falls. So you should also consider anchoring the appliance to the floor or wall.
Estimated Cost: Having a flexible connection installed on a furnace orother large appliance will cost you about $75.
As shown in the figure, the sill plate of a house rests directly on top ofthe foundation. (This figure shows the sill plate for a house built on a cripplewall and crawl space foundation, a type of construction that is especiallysusceptible to earthquake damage.)
If the sill plate is not securely anchored,an earthquake can cause it to shift on the foundation. When this occurs, thereis a greater potential for severe damage as well as injury to you and members ofyour family.
One way to increase the stability of your house and reduce earthquake damageis to have the sill plate bolted or otherwise anchored to the foundation.
In themethod shown in the figure, bolts long enough to pass through the sill plate andpenetrate several inches into the foundation are installed every few feet alongthe base of the exterior walls. This method is not limited to cripple wallconstruction; it can also be used for a house built on a basement orslab-on-grade foundation or on another type of crawl space foundation.
Tips -- Keep these points in mind when you have the sill plates bolted to thefoundation :
- Modifications to the foundation of your house must be done by a licensedcontractor, who will ensure that the work is done correctly and according to allapplicable codes. This is important for your safety.
- Bolts are usually installed no more than 6 feet apart. The work involved islikely to be extensive and may require that portions of the walls or floor becut away temporarily.
- Your contractor may be able to recommend an alternative anchoring methodbased on other approved fasteners or connectors that can be installed with fewerchanges to your house and less work.
- If your house is built on cripple walls, you should consider bracing themafter the sill plates are bolted.
Estimated Cost: Having a contractor bolt the sill plates to the foundation will cost youabout $50 to $75 per bolt, depending on the type of foundation you have. Forexample, a house measuring 60 feet by 30 feet, will have a perimeter of 180 feetand would therefore require a minimum of 30 bolts (if the bolts are placed nomore than 6 feet apart). So the cost for that house would be about $1,500 to$2,250.
Somehouses are built on cripple walls. As shown in the figure, a cripple wall is ashort wall that rests on the foundation and supports the floor and exteriorwalls.
If the cripple wall is not braced, it can shift during an earthquake. Whenthis occurs, there is a greater likelihood that your house will be severelydamaged and that you and members of your family will be injured.
If your house is built on cripple walls, one way to increase its stabilityand reduce earthquake damage is to brace the cripple walls. In this method,horizontal blocking that consists of 2" by 4'' boards is added between thevertical studs at the top and bottom of the cripple wall and, if necessary, atother locations between the studs. New vertical studs can also be added ifnecessary. Plywood or oriented strand board is then nailed to the interior faceof the cripple wall. Also, nails are added through the existing blocking betweenfloor joists to ensure that the floor is securely attached to the cripple wall.
Tips -- Keep these points in mind when you brace cripple walls:
- Check with your local building officials to see whether you need a permit to do this work.
- Before adding any bracing, check to see whether the sill plate below the cripple wall is bolted or otherwise anchored to the top of the foundation. If it is not, you should consider having bolts or anchors added.
- Any anchoring of the sill plate should be done before you add bracing.
Estimated cost: Bracing a 2-foot-high cripple wall will cost you about$1.50 per linear foot of wall. For example, a house measuring 60 feet by 30 feetwill have a perimeter of 180 feet. So the cost for that house would be about$270. This figure covers only the materials you will have to buy and excludesthe cost of any tools you use, building permit fees, and the value of your time.This figure also excludes the cost of having a contractor anchor your sillplates. Also, bracing higher cripple walls may require more lumber and thereforemay be more expensive.
Other Sources of Information:
- Seismic Retrofit Training for Building Contractors and Building Inspectors:Participant Handbook, FEMA, 1995
- Reducing the Risks of Nonstructural Earthquake Damage: A Practical Guide,FEMA-74, 1994
- Protecting Your Home and Business from Nonstructural Earthquake Damage, FEMA,1994
- To obtain copies of these and other FEMA documents, call FEMA Publications at1-800-480-2520.
- Information is also available on the World Wide Web at http//:www.fema.gov.
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