Is the foundation bolted? Yes. But………….(you knew there had to be a “but”)

     In my many years as a builder----and in my more recent incarnation as a Seattle Home Inspector-----something that I have noticed about houses is that they can be very forgiving structurally.  Complete structural failure of a component is sometimes difficult to arrange.  Other times, with the requisite conditions, we will see the weekend warrior’s deck go all kittywampus in the back yard----with the beer keg rolling down the street as the ambulance pulls into the driveway.

     How does the house know which rules to break and which ones not to break?

     Take foundation bolting for example.  It is a question I get asked often----is the house bolted to the foundation?  Over the course my building career I have seen foundation bolting go from ½” bolts, 6-8 feet apart, with no washers under the nuts, to 5/8” bolts, every four feet, with 2” square-plate washers under the nuts.  In addition to this bolting are all manner of seismic strapping and hold-down bracketss with bolts as big as 1-1/8” in diameter.  And this is in residential construction----commercial is even more extensive.

     All of this is fine and dandy and will likely help your house do very well in seismic activity up to a 7 or a little higher on the Richter scale.  After that, all bets are off supposedly----but still the amount of damage would have to be somewhat less.

     Again I ask, “How does the house know which rules to break and which ones not to break?

     You see, the other day, I inspected a house that was over 30 years old.  Its age tells me that it has been through at least two fairly major earthquakes in this region-----including the 2001 Nisqually Quake.  The house had no visible damage and yet the foundation bolting---while present----looked like the following picture.

     This bolting is almost worse than no bolting at all----as the sill plates are nearly completely severed every 6 feet.

     So the insurance company wants to know if the house is bolted.  Any inspector would be “nuts” to say that this foundation is “bolted” wouldn’t they?  And yet the house is doing fine after 30 years and is “standing the test of time.”

     The house has broken the “rules” and is doing fine.  Keeping houses on their foundations is not restricted to or dependent on code requirements for bolting.  There are many older homes in Seattle that are not bolted to their foundations at all and have little or no seismic damage going back to earthquakes even stronger than any this house wiggled through.

     For example there was a method of pouring foundations in this area, that used to be very common, where the bottom plate of the wall was put right in the forms so that when the concrete was poured it actually came up higher on the plate all the way around the inside of the foundation.  This created an installation where the wood walls were naturally locked in place laterally by the concrete wall itself.

     The reason this 30 year old house has done so well is because of the many “steps” in the foundation.  Stepping the foundation aids in interlocking the foundation and wood walls, thus restricting movement laterally.  If we take the same house with a uniform foundation---with no steps-----and did the same type of bolting as in the second picture, the house would likely not fare as well.

     As you can see, answering the seemingly simple question of whether the foundation is bolted or not does not really provide much in the way real information to anyone. 

     How the house is performing in relation to its age and methods of bolting is much more useful information to provide.

Charles Buell, Seattle Home Inspector