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Inadequate Floor Joist Connections Specified in Building Code

The current 2016 California Building Code contains a specification that make homes “built to code,”  vulnerable to earthquakes.The code specifies that only 3 nails be used to connect the floor to the foundation on two sides of the house to meet the requirements of the building code. This is inadequate.

TABLE SHOWING HOW ONLY 3 NAILS ARE POSSIBLE IN A HOME'S FLOOR JOIST TO MUDSILL CONNECTIONS

TABLE SHOWING HOW ONLY 3 NAILS CONNECTING THE JOISTS TO THE MUDSILL ARE CODE COMPLIANT

This means  wherever the joists or girders sit on top of the mudsill, only 3 nails need to be installed in order to meet the legal requirements of the building code.

Before the use of nail guns became pervasive, driving nails with a hammer was arduous and caused an injury known as “carpenter’s elbow” This caused contractors to only meet minimum building code standards through the installation of only 3 nails as a way to increase speed, avoid injury, and minimize fatigue.

Below is an illustration of what it looks like under your house. Floor joists (or girders) support the floor you walk on. These in turn are supported by a piece of redwood called the mudsill. If the floor joists or girders slide on top of the mudsill, the house can be damaged.

EARTHQUAKE FORCES TRYING TO PUSH FLOOR OFF FOUNDATION AND DEFICIENCY IN BUILDING CODE

Diagram: Earthquakes exert force that may push the floor off the foundation. The current building code specifies 3 nails in the end joists to resist this type of force which is clearly inadequate.  

After nail guns were invented, contractors may have chosen to exceed the code, but there is no way to know for sure without taking off the stucco or wood siding. In any event, houses built before 1978, before nail gun use became pervasive, are almost guaranteed to have this problem.EARTHQUAKE MOVEMENT RESTRAINED BY SHEAR TRANSFER TIES

Diagram: To remedy the deficiency in the building code special hardware called shear transfer ties or framing anchors should be used.

Why Aren’t Building Codes Followed?

Implementation of the Building Code is the job of the contractor. The job of building inspectors is to make sure contractors follow the code. When contractors rush their work in order to save money, seismic provisions in the code may not be implemented properly. Contractors and building inspectors also may not adequately understand the importance of seismic provisions in the code. Both of these issues may lead to poor workmanship and homes that are not adequately strengthened for earthquakes. Unfortunately, during construction, most time-pressed inspectors only have a few minutes to look at a house while it is being built, and deviations from the building code are often missed. The almost universal installation of bolts in over-sized holes, which the code forbids, is a case in point.

A Real Life Example: Over-sized Bolt Holes

 

FOUNDATION BOLT IN OVER-SIZED HOLE IN MUDSILL. THIS VIOLATION OF THE BUILDING CODE IS THE RULE RATHER THAN THE EXCEPTION

FOUNDATION BOLT IN OVER-SIZED HOLE IN MUDSILL. THIS VIOLATION OF THE BUILDING CODE IS THE RULE RATHER THAN THE EXCEPTION

Bolts are a vital component in new construction as well as in a seismic retrofit. Unfortunately, bolts will not be effective in resisting earthquakes because almost universally they are installed in over-sized holes where the diameter of the hole in the wood exceeds the diameter of the bolt.  The 2016 California Building Code prohibits installation of bolts into holes exceeding 1/16 of an inch larger than the bolt diameter:

Bolt Holes

Bolt over-sizing occurs because at the time of inspection the bolts are installed with nuts and washers such that the size of the hole is not visible, and because contractors are unaware of how important this is, and because it is easier for contractors to have over-sized holes so they can adjust the mudsill.

Mudsill Viewed from Above

House Bolt Failure caused by Over-Sized holes

When Bolts are Over-sized they do not work together until the mudsill splits at each bolt location.

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