This web page has a history. I wanted to compile an album of every photograph of residential cripple wall damage I could find on the internet. In my research I soon noticed that almost all of the homes where the cripple walls collapsed had wood siding rather than stucco. Here we will see why.
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 51 and 52, where I can say with certainty that the stucco clad cripple walls had collapsed.
Remarkably, most seismic retrofit guidelines require more retrofit components for houses with stucco siding and less retrofit components for houses with wood siding even though wood siding is more vulnerable. This is because from an engineering/mathematical point of view stucco homes are heavier and at greater risk. This is in spite of the fact empirical evidence reveals stucco clad cripple walls are in fact at much less risk. This is a case where mathematics confronts evidence and evidence should prevail.
This information in this video will help you decide which parts of your house are already earthquake resistant versus structural weaknesses that need to be strengthened.
HOW CAN WE PREDICT WHICH CRIPPLE WALLS WILL COLLAPSE?
The weakest part of a house will fail first. Invariably this means the cripple walls on the transverse walls. Most houses have transverse walls that are 25′ wide and longitudinal walls 50′ long. The longitudinal walls are inherently twice as strong as the transverse walls. This is because siding of any type, either wood or stucco, does have some earthquake resistance. A longitudinal wall 50′ long has twice the amount of earthquake resistant siding as a 25′ wall and is therefore twice as strong. This is why in all the photos listed below, except photos 51,52,and 53 , the transverse cripple walls have collapsed rather than the longitudinal cripple walls.
It should also be noted that wood siding described in TABLE A1-D of the CEBC (the California Existing Building Code) as “Floors with straight tongue and groove sheathing” has half the strength of stucco which is described as “plaster on wood or metal lath”. As you can see wood siding can resist “300 lbs. per foot for seismic shear” while stucco can resist double that at “600 lbs. per foot for seismic shear” This further explains why the earthquake resistance of wood sided houses is much less than houses with stucco 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 ONLINE THAT LOOKED LIKE IT HAD A CRIPPLE WALL COLLAPSE. ON CLOSER SCRUTINY IT APPEARS THIS DAMAGE MAY HAVE NOT BEEN A CRIPPLE WALL COLLAPSE AT ALL. THE DAMAGE WAS PROBABLY CAUSED BY THE END JOIST SLIDING ON THE MUDSILL.
IMAGE 51 STUCCO CRIPPLE WALL COLLAPSE. THIS IS ON A LONGITUDINAL WALL WHICH MEANS THE TRANSVERE CRIPPLE WALLS COLLAPSED.
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 IMPROPERLY 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.
