If you live in an area where earthquakes are likely to occur, it’s important to ensure that you’ve done everything you can to strengthen your home foundation against earthquake damage. Thankfully, a few simple upgrades may be all you need to keep your house from sliding off its foundation during an earthquake. Depending on the condition of your foundation, you can tackle the work yourself for as little as $500, or you can hire a contractor for about $2,000. Whatever you decide, you stand to avoid repairs that could cost you tens of thousands of dollars. Earthquake insurance often carries a substantial deductible, so it is important to take measures to secure your home regardless of whether your home insurance covers earthquake damage. If you live in California and are planning on selling your home, the state requires that you specify whether earthquake strengthening measures have been installed.
New homes built to current building codes should be strong enough to keep people safe during an earthquake, but older homes usually need strengthening. It’s important to consult with your local building department to see if you need simple upgrades or help from a structural engineer. It’s also important to take care of earthquake strengthening before closing off access to walls. The best way to implement earthquake strengthening can depend on what type of foundation your home has. So, we’ve outlined below a few basic measures you can take to earthquake-proof your home according to foundation type.
Poured Perimeters to Strengthen Your Home Foundation
If your house sits on a wall of poured concrete with a few posts in the center under beams, you have a poured perimeter foundation. With poured perimeter foundations, there is often little more than a few nails and gravity to hold the home in place. So, if you have a poured perimeter foundation, your first step is to establish whether your home requires earthquake strengthening.
You’ll want to go into the crawl space or basement to look for thick bolts along the top of the sill plate (the bottom horizontal member of a wall or building) and steel anchor plates that tie an edge of the sill plate to the side of the foundation. By contrast, if neither of these things is present, you’ll want to install them. Additionally, when the first floor of your home sits several feet higher than the perimeter foundation, you should also check the short “cripple” walls on top of the sill plate. If your cripple walls are satisfactorily braced, you will see diagonal boards or plywood on the outside of the studs. If you don’t see diagonal boards or plywood, add bracing by nailing plywood to the interior side of each wall. Unsure how to do this? Give us a call and get a free estimate!
Unreinforced Masonry Foundations
If the concrete blocks that make up the perimeter of your foundation are filled with rebar and concrete, then you can retrofit the foundation in the same way you would a poured perimeter foundation. If the blocks are hollow, you should consult with a structural engineer. Typically, you can expect to spend $500-$700 for a structural engineer’s evaluation and recommendation. Keep in mind that a taller foundation is more structurally sound than a short foundation. Short block walls are more vulnerable to collapse because they have fewer mortar joints, leading to a concentration of stress in each joint. If your foundation consists of only a couple courses of blocks or if the walls are in bad shape, you might need a new foundation. Typically, a new foundation can cost around $40,000 and will often cost more for a home without a basement.
If your home rests directly on a concrete slab, you should make sure that metal straps or bolts tie the sill plate to the concrete. You can check sill plates by removing a section of drywall or siding in an unobtrusive spot. If you are planning on removing any siding or drywall for a future project, it’s the perfect time to check for straps or bolts and add them if needed. However, if you do not have any plans to open up a wall, you can rest easy knowing that the likelihood of your home collapsing is minimal because it doesn’t have far to fall.
Post and Pier Foundations
If your home rests on upright posts on concrete blocks and piers, you should consider either bracing the posts or adding a new foundation. If you choose to brace the posts, you can expect to pay about $1,000, but adding a new foundation can cost around $25,000. Another option is pouring short L-shape concrete foundations around each corner, securely attaching them to the floor framing. To assess which option is best for your home, consult a structural engineer.
If you need to help to evaluate the best way to strengthen your home foundation, call us today at (818) 616-8106!