Definitions of Retrofit Terms

Anchor Bolt

Anchor bolts are used to secure the mudsill to the foundation. An anchor bolt is a metal rod, usually with a threaded end, that is set in concrete and is embedded in the foundation or is installed in existing concrete.


Metal Connectors

Connectors are steel components that connect the frame of the house together. Connectors are used where two pieces of framing material meet. They are designed to strengthen a home increase its ability to withstand earthquakes.


Crawl Space

Crawl space refers to the space beneath a home, typically 18 to 48 inches high that is supported by short wood-framed walls known as cripple walls.


Cripple Walls

Cripple walls are short wood-framed walls between the first floor and foundation. They run underneath and around the perimeter of a house. These walls are constructed on top of a home’s foundation and are generally 12 to 30 inches high, but as high as 12 feet when located on a hillside. Cripple walls are vulnerable to earthquake damage and should be properly braced and bolted to the foundation.



A foundation is the block wall, concrete wall or concrete slab on which a house sits.


Hold Down (HD)

A high-strength fabricated stell screw anchor that is used to attach the mudsill to the foundation for resistance to uplift forces.


Joist (Rim Joists, Floor Joists, Pressure Blocking)

Joist refers to the wood members that make up part of the structural floor system of a house. Rim joists run along the perimeter of the floor system. Pressure blocks refer to blocking that is installed between floor joists to prevent collapse or lateral movement.


Lateral Forces

Lateral forces are horizontal forces acting to move a home from side to side.



Load is an engineering term that refers to the weight of the material that is to be supported.


Mudsill (Wood Sill or Sill Plate)

A mudsill is the wood frame that attaches to the top of the foundation and to the floor system above. The mudsill should be properly bolted, with plate washers, to the foundation.


Post (Column)

A post is a load-bearing vertical wood member.



A shearwall is a reinforced wall in a home that has been engineered to help resist the lateral forces that are caused by an earthquake, hurricane or tornado.



A stud is a vertical wood member in the framework of a wall for supporting framing and finishing materials.


Universal Foundation Plate (UFP)

The Universal Foundation Plate (UFP) is a metal connector that connects the mudsill to the foundation. It is used when cripple walls are less than 3 feet tall or the mudsill is slightly offset from the foundation.


Uplift Forces

Uplift forces are vertical forces acting to lift a home.


Ventilation Holes

Ventilation holes are circular holes that are cut into sheathing to help prevent the wood from decay and rot. Proper ventilation is important when installing new sheathing onto the inside of cripple walls.