Home & Garden Columns

About the House: Retrofitting a Lousy Foundation

By Matt Cantor
Friday August 10, 2007

We had a little shaker a few weeks ago and I was faced with the same series of encounters in the ensuing days that I’ve faced so often over the last 20 years. They tend to go something like “Hey, that was a pretty big quake we had the other day, eh? But you know, there weren’t any cracks in my walls or anything. Not as bad a Loma Prieta.” And I get started… “Well, the fact is that what we had the other day was tiny.” Then comes the math. “Did you know that a 7.2 on the Richter is roughly 30,000 times bigger than a 4.2 (the one we just had)”…faces go blank, people wander away wondering why they bothered talking to me in the first place. Maybe I’m just not a people person. Oh well, my kids love me. 

Those are the facts and I’ll beleager you just a bit more before I move on to practical matters. First, all those earthquakes your house has been through…They’re nothin’. Just plain nothin’. The last earthquake that hit our town that was worth any serious attention at all was well over a hundred years ago, in 1868. Andrew Johnson was being impeached and UC was being founded (in Oakland of all places). The 14th Amendment was being passed to give African Americans full rights (and corporations the right to rule our lives) and Thomas Edison was applying for a patent for the first electric voting machine (no, I am not kidding). The point is that this was so long ago that nobody living can remember it and there are effectively no structures standing today that can give evidence of what that earthquake was like.  

It’s likely that when we do get our earthquake (Loma Prieta was somebody else’s earthquake) that over 150,000 homes will have to be abandoned and the occupants consigned to refugee status. If you don’t want to be one of those folks—and I assume you don’t—then it’s time to bolt and brace your house. If you’ve had it done years ago or by someone of less than definitive credentials then it makes sense to have it looked at. There might be some need for improvement. 

Now, I have this bad habit of taking a long time to get around to what I wanted to talk about and so I duly apologize if I’ve wasted some of your time. I guess I needed a prelude. So, that being done, here’s what I wanted to get to: 

A lot of homes have bad foundations. Now, that’s a rather broad remark, so I’ll try to clean it up a bit. Many foundations, especially those from before 1935 suffer from a range of ills, including concrete deterioration (soft concrete), rotation (tilting of the footings) and cracking (or settlement). These can, in combination, be serious enough to require replacement of part, or even all, of your foundation. In my book, serious deterioration is the most serious failing when it comes to earthquake readiness because it keeps bolts from staying in one place when the earth starts shaking. When foundations are really crumbly (you can drive a screwdriver an inch through) there may not be any point in adding bolts. But I firmly believe, having sat down with a number of engineers and other experts over the years, that all but the worst foundations can be retrofitted to some effectiveness.  

Even foundations that have settled badly, those with cracks and fairly serious rotation, can have bolts and bracing panels installed with reasonable assuredness that they will add greatly to the earthquake resistance of a house. The reason I point this out is that many people are putting off doing seismic work until they get to the foundation and this can mean, due to the high cost, a delay that may end badly. 

The earthquake isn’t going to wait for all of us to upgrade our foundations, so we need to decide which ones we’re going to do and retrofit the rest of them to our best ability. Most retrofits are not going to fail as a result of a bad foundation and there are many faulty foundations that will work more than well enough if bolts and bracing panels are properly installed. So, if you don’t have cash to fix the foundation this year, it’s time to do the retrofit. 

Here are some pointers for those who know that they have poor quality concrete and are ready to get this vital task completed. First, use more bolts. When concrete quality is poor it’s beneficial to distribute the lateral load of the house (the weight of the house moving left and right) over a larger area. By putting more bolts into the older, softer concrete, we put less stress on each portion and decrease the likelihood that the bolts will break through the concrete. Here’s a freebie we get from doing this: since weaker concrete tends to vary in strength as we move around the perimeter of the foundation, we increase the chance that some bolts will be in better concrete and will stay in place. In the end, all we need to do is to be sure that enough of the house is grasped and held in place to prevent it from sliding off of the foundation. 

Another thing that I recommend for weaker concrete is the use of epoxy for bolt installations. Yes, we’re talking about gluing the bolts in place. This may sound silly or weak but it’s just the opposite. When concrete is crumbly, the typical expansion bolt doesn’t work very well. This is a bolt that, when tightened, enlarges in diameter near the base, thus lodging it in place. If concrete is soft, this enlargement can just push some rocks and sand around and actually weaken this area all the more. Not only does this weaken the area immediately around the bolt but also leaves the bolt loose and more able to slam through soft concrete. Epoxy, on the other hand, strengthens the area immediately around the bolt, fills any voids and bonds the bolt to the foundation. It’s a much better connection for weak concrete. 

Once again, many retrofits have been poorly done and it’s a good idea to have someone look at them. Nevertheless, poor concrete is only occasionally so bad that that a retrofit isn’t worth the money. This local fault has been pretty faithful to its schedule and has us now about a decade overdue. Even if you end up reinstalling bolting and bracing in five years when you get that new foundation, I still think it’s wise to go ahead and spend the money to bolt and brace to that old broken concrete today. The alternative may be hundreds of thousands of dollars in damage that could have been avoided with just a few thousand spent now. 

Insurance may recoup some of your losses when that day arrives or it may not. If this quake is centered in a densely developed area (It’ll probably be at my house), the cost may be more than the underwriters have set aside and you may not be made whole (financially speaking).  

John Lennon said “Life is what happens to you when you’re busy making other plans.” I don’t think there are many earthquakes in Liverpool so I have no idea how he understood this problem so well. 



Got a question about home repairs and inspections? Send them to Matt Cantor, in care of East Bay Real Estate, at realestate@berkeleydailyplanet.com.