This web page has a history. I wanted to compile an album of every photograph of residential cripple wall damage that I could find on the internet as well as some original research. In my research I soon noticed that almost all of the homes where the cripple walls collapsed had wood siding rather than stucco.
In the photo album below you will see numerous homes with wood siding that have suffered catastrophic cripple wall damage and only two cases, image numbers 12 and 51, where I could with absolutely certainty confirm that it was a stucco cripple wall collapse. This observation could have been expected based on the Rockwell Tests discussed in this video.
I suggest you watch the whole video which looks at the parts of the house that are already very earthquake resistant and can be left along, and the parts that need to be strengthened with a home seismic retrofit. If you just want to look at the science I make my point clear from minute 15:00 till the end 7 minutes later
THIS IS WHAT HAPPENS WHEN CRIPPLE WALLS COLLAPSE
All the extant seismic retrofit guidelines require more retrofit components for stucco homes than homes with wood siding. In the 50 photos of collapsed cripple walls you will see here, only one houses has a collapsed cripple wall that is covered with stucco. All the rest of the houses have cripple walls covered with wood. This is not to say that cripple walls covered with stucco have the potential to collapse, but based on empirical evidence it is far less frequent than these guideline authors might imagine. The photos here were primarily gathered from Google Images as well as some original research after the Napa Earthquake in 2014′
Cripple wall collapses exclusively occurred at the front and back of these homes. This is because the length of the front and back cripple walls is usually half the length of the cripple walls on the two sides. Most houses are 24 feet wide by 48 feet long. The 48 foot long cripple walls will have twice as much plywood on them as the 24 foot long walls.
Stucco has a considerable amount of strength as is, which means cripple walls that are 24 feet long are inherently half as strong as the 48 foot long walls.
Earthquakes cause the weakest parts of a house to fail first which means these sorter weaker shorter cripple walls will fail before the longer cripple walls. It is also true that wood siding tongue and groove siding. has half the strength of stucco according to the California Existing Building Code. It is therefore not surprising that all but one of collapsed cripple walls are covered with tongue and groove siding. This is confirmed by the Rockwell Tests that evaluated the earthquake resistance of old stucco and wood siding. The table below represents the conclusions of this test.
“Floors with straight tongue and groove sheathing” responds to earthquake forces exactly like wood walls made of made of tongue and groove siding. Tongue and groove siding are the horizontal boards you will see on the outside of a house. Almost all of the houses in the rest of this web page with collapsed cripple walls have horizontal siding.
Comparison of Wood Siding (tongue and groove sheathing) and Stucco
THIS IS AN EXAMPLE OF A CRIPPLE WALL
THIS IS AN EXAMPLE OF A CRIPPLE WALL THAT HAS BEEN BRACED WITH PLYWOOD TO PREVENT COLLAPSE.
THIS IS AN EXAMPLE OF A CRIPPLE WALL COLLAPSE BECAUSE THE EXTERIOR PLYWOOD BRACING WAS NOT NAILED PROPERLY.
THE NEXT 49 PHOTOS ARE EXAMPLES OF COLLAPSED CRIPPLE WALLS
ONLY IMAGES 46 AND 47 CAN BE IDENTIFIED HOMES WITH COLLAPSED CRIPPLE WALLS.
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IMAGE 50 IS ONE OF TWO STUCCO HOUSES I COULD FIND ON LINE THAT HAD A CRIPPLE WALL COLLAPSE. EVEN THEN, THIS DAMAGE MAY NOT HAVE BEEN A CRIPPLE WALL COLLAPSE AT ALL AND THE DAMAGE WAS CAUSE BY THE END JOIST SLIDING ON THE MUDSILL.
IMAGE 51 STUCCO CRIPPLE WALL COLLAPSE.
IMAGE 52 STUCCO CRIPPLE WALL COLLAPSE TO APARTMENT BUILDING. THE UPPER DECK AT THE BACK IDENTIFIES THIS AS A MULTI-STORIED APARTMENT BUILDING,
IMAGE 53 THIS HOUSE LOOKS LIKE STUCCO BUT THE MATERIAL THAT FELL OFF THE CRIPPLE WALL LOOKS LIKE BADLY NAILED PLYWOOD
Below Are Photos of Damage to Homes That Do Not Have Cripple Walls
IMAGE 54 END JOIST SLID ON MUDSILL
IMAGE 55 MINIMAL SLIDING OF END JOIST ON MUDSILL
IMAGE 56 THE ONLY INSTANCE I FOUND WHERE THE HOUSE HAD WOOD SIDING, DID NOT HAVE A CRIPPLE WALL AND THE END JOIST SLID ON THE FOUNDATION.
