THIS IS A SAMPLE PROPOSAL THAT ALSO DESCRIBES THE PRINCIPLES AND PRACTICES BEHIND EVERY NO CIPPLE WALL RETROFIT
Bolting Homes Without Cripple Walls
This is one of two types of homes that qualifies for the State Brace And Bolt Program.
The Blue Arrow Points at the top of the Foundation, the Red Arrow at the Floor you Walk on. There is not a wall Between the two. This means you do not have a Cripple Wall.
Damage to homes without cripple walls
What Happens in a No Cripple Wall Retrofit
This an image of what it looks like under your floor when you do not have cripple walls. When bolting a house, one must attach the floor joists, rim joists, end joists, and mudsill to the foundation so they don’t slide off of it. The red arrows represent earthquake forces trying to push the floor off the foundation.
Foundation Anchors: Securing Your House To The Foundation
Foundation anchors attach the bottom of the house called the mudsill to the concrete foundation. Foundation anchors attach the mudsill to the foundation from the side, while standard bolts do it from the top. Limited vertical clearance for tools prevents standard bolt installation.
This is one of the more common kinds of foundation anchors. Contractors and engineers use many kinds of foundation anchors. The precise type depends on its ability to fit the existing framing style. Framing styles used before building codes commonly had many variations. Each variation requires its own approach.
This is a manufacturer’s photo of a foundation anchor
This is the same hardware installed under a house. The earthquake force tries to push the mudsill off the foundation. The bolts in the foundation anchor prevent this from happening. We have bolted the house exactly as if we used standard foundation bolts but have done it from the side of the foundation.
This is another type of foundation anchor.
In the upper left corner, you can see how the manufacturer bent this foundation anchor so it can fold over and be nailed to the top of the mudsill.
Bolting Floor Joists to the Mudsill
Earthquake forces push the end joists and rim joists off the mudsill. Shear transfer ties, also known as framing anchors, as shown by the black arrow, counteract that force.
Shear transfer ties connect the side of the floor joist to the top of the mudsill with nails. When the floor joist tries to move, the shear transfer tie transfers that sliding force to the mudsill. The mudsill does not move because it is bolted to the foundation.
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Earthquake forces pushed on floor, house slid off foundation
Even though the mudsill of this house was bolted to the foundation, damage occurred because there wasn’t a strong connection between the mudsill and the floor. Shear transfer ties would have created a strong connection between the floor and the mudsill, and thereby prevented the house from sliding off the foundation.
When Standard Foundation Anchors Won’t Work on Your House
It often happens that foundation anchors and shear transfers ties will not work for various reasons. The primary cause is that a standard hardware won’t fit. In these cases, one must develop custom solutions. The most common approach is to bolt a new mudsill to the side of the foundation and attach the floor to it.
We bolted a new mudsill to the side of the foundation and connected it to floor with plywood.
Here is a complete system with a new mudsill bolted to the side of the foundation. This along with the shear transfer ties work together to keep the floor from moving.
A Problem with the California Building Code
See TABLE 2304.1 of the current California Building Code below. It requires only 3 nails, or 3 staples to attach the full length of a floor joist to the mudsill. An 8d common is a type of nail. The mudsill is the piece of wood bolted to the foundation – see the diagram below the table.
Three nails are not enough to keep a floor joist attached to mudsill. It can slide off. However, before nail guns came into common use in the mid-seventies, driving nails by hand was hard on the arm and extra nailing cost the contractor money. Three nails is clearly insufficient for a 12-24 foot floor joist – that’s why we need shear transfer ties to strengthen the connection between the floor joists and the mudsill.
FRAMING ANCHORS (SHEAR TRANSFER TIES) COMPENSATE FOR THIS DEFICIENCY.
