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Top Plates and Cripple Wall Retrofits

 Top Plates and Cripple Wall Retrofits

In typical East Bay homes that need a cripple wall retrofit, the entire weight of the house sits on top of the cripple wall.  The horizontal board on top of the cripple wall is known as the upper top plate.

Cripple wall retrofits consist of converting the cripple walls into shear walls. Shear walls need continuous connection to the floor that sits on them.  This restrains the entire floor from moving.  The critical point to remember is that all the weight of the house sits on the upper cripple top plate.  If there are breaks in the upper top plates, you will not have the continuous connection that you want.  For example, if a shear wall holds the house to the foundation at one end of the house,  but not the other end, the house will sustain damage.  Building codes  forbid breaks in continuity in cripple wall top plates to prevent this.

Cripple Wall Retrofits and Top Plate Continuity

Cripple Wall Retrofits and Top Plate Continuity

Cripple wall top plates are actually segments of wall that can move independently of each other, boards that are 8 to 24 feet long butted together.  Any point where they butt together is called a top plate break.   These breaks create a break in continuity, meaning the pull and push of the earthquake force is not continuous along the cripple wall top plate.

  • In the diagram above, the cripple wall to the left of the break in the top plate is disconnected from the shear wall to the right of the break in the top plate.  If there were no break and the top plate were one piece, then the two would be joined together, and any movement of the cripple wall would be restrained by the shear wall.  Hence the top of the cripple wall and the top of the shear wall must be connected together so they cannot move independently.
  • The break in the top plate must be connected so the floor responds to earthquake forces as one unit.

 

Restoring Cripple Wall Top Plate Continuity

Steel straps and nails are the two methods by which continuity is restored.

In this image, a steel strap connects the two sections of the top plate.

Top Plate Strap

 

Another way to do this is with nails

 

Cripple Wall Retrofits improved with Nails

Cripple Wall Retrofits improved with Nails

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San Jose,Sunnyvale, Fremont,Oakland,Berkeley
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