Home & Garden Columns

About the House: The Amazing Simpson Universal Foundation Plate

By Matt Cantor
Friday July 06, 2007

Now, this has happened to everybody at some point. You think of this cool thing that would make something work better and then one day, you’re walking (or in my case crawling) along and lo and behold, there it is! Well I have to admit that when I saw the one that Simpson company (of our own beloved San Leandro) had come up with, I realized that the one in my mind wasn’t as good. Nevertheless, It’s still amazing when something institutional, large-scale and corporate turns out to be clever and just the right size and price. 

Simpson is a pretty great company and for those of us in light construction (watching our weight, as it were) they’re a Buddha-send. Not only do they make a huge array of very nicely designed parts that make it easy to put houses together (or fix them), they also do tons of research into how earthquakes damage houses, how wood fails and how workers need to do their jobs. They also provide great documentation that makes it easy for someone like me to find the right thing or to see if you used the right hanger, bolt or strap by labeling things in innovative ways. I like these folks. 

So let me tell you a little about my favorite Simpson™ product because for we Estuarians with our 90 year old houses, it’s a terrific asset and can not only save your house, it can also save you money (that part comes later). 

A lot of seismic retrofitting (the bolting and bracing of houses for earthquake readiness) involves the bolting of houses in those very short spaces below your floor. These spaces are often so short that bolting down is not an option. There’s just no way to drill that way. 

Over the years, I’ve seen a lot of interesting attempts to fasten houses to their foundations in these confined settings. Some of it gets pretty comical from a geeky sort of perspective (these “in” jokes require you to know how the forces work but trust me, some of the attempts are genuinely funny). 

Engineers and contractors have tried all sorts of ways to attach the house to the foundation when there’s no room to bolt downward and the short answer is that most just don’t work or are so hard (or expensive) to do that they just don’t end up getting done right. 

That’s why the Universal Foundation Plate (UFP) is so cool. It makes it easy. This “plate” is very Star Trek in its shape and concept. Unlike most construction hardware it’s neither flat nor folded. Rather, it’s been cleverly articulated to optimize its strength in performing one special function; to keep mudsills (and houses thereby) bound in place. 

There’s another problem with this bolting thing. The stick of wood (or “mudsill”) that you’re trying to bolt to the concrete foundation is pushed back sometimes several inches from the inside edge, so if you’re trying to fasten the two together, you’ve got some work to do. 

They just don’t meet properly. It gets worse. Many older foundations also tilt inward on the inside face. So now you’ve got an inclined surface and a ledge of a couple of inches and then a piece of wood that you have to grasp and hold under enormous forces. 

Formerly, the best thing we had to do this job with were shop-cut lengths of L shaped metal that we could bolt from the footing to one of the floor joists. According to at least one local engineer, the bolting from this to the joist puts too much force in one place and can just split that joist apart. I also will often see straps used in this setting that will easily allow for sliding motion and may only tighten up after the house is inches off the foundation. 

As in many parts of retrofitting, the key is to distribute the force during all that shaking so that many parts share the load in order to keep any one part from busting apart. Good distribution of forces is key in good retrofitting. 

Now I realize that this is all a bit esoteric but please hang with me. It’ll be worth it. 

The UFP is just the right shape to do the trick I was describing above. It lies over the inclined footing, reaches out across the gap to that wooden board (incidentally called a “mudsill” because it rests on the formerly wet concrete or “mud”) and screws into the sill with a set of stainless steel screws. 

We don’t usually use screws in seismic work because they tend to snap but these are very specially made for just this function. The bottom of the UFP has a couple of bolt holes and one need only drill into the concrete from the side (easily accomplished using a special drill called a “roto-hammer”) to secure it in place. 

Another nice use of this cool product is in the addition of fasteners to walls that have already been braced and now have no access to the tops of the mudsills. Some buildings I see have had braced panels or “shear-wall” sheathing already added. Someone’s done a retrofit. But we can’t see how many bolts are present or know that there are just not enough. Shall we rip out the braced plywood panels and start again? With the UFP, we have an alternative course. If the panels appear well-installed or simply need some more nailing (and many lack enough nailing or need more due to nails driven too far into the plywood, thus weakening these connections) we can leave the panel in place and put a UFP at the base and screw it into the mudsill right through the plywood. 

This can save thousands on a retrofit. It can also solve a problem I often face, which is just-not-knowing how well the walls are bolted. 

When in doubt, it may be too much to ask to remove walls to see, but it’s not that hard to simply add a few of these novel widgets to compensate for what might be too little bolting. So they’re cheap confidence and real protection against what earthquakes are good at. Namely, tearing houses free from their foundations. 

UFPs are also easy to work with and pretty hard to screw up. I see a lot of bolting and bracing in my job—more than almost any other group of professionals. And I see a lot of mistakes. So it means something for me to say that I almost never see UFPs installed incorrectly. 

Yes, I have seen too few used and I think I’ve seen them poorly placed (they need to be near the ends of every piece of mudsill and spaced apart according to the size of the building) but I can’t recall seeing too many actually put in where they would not do any good.  

Surprisingly, bolts are often installed so that they provide far too little security, so it’s no small joy when something is designed that is, at least, somewhat foolproof. Of course you know what they say, don’t you?  

Nothing is truly foolproof when in the hands of a sufficiently talented fool! 


Matt Cantor owns Cantor Inspections and lives in Berkeley. His column runs weekly. 

Copyright 2007 Matt Cantor