Slide 6 of 13
- HOLD-DOWN ANCHORS ARE NEEDED
- The purpose of hold-down anchors and their proper installation are discussed in the part of the manual titled Connections to Resisting Uplift Forces and in the section on Shear Walls.
- In the partial perimeter system
- Hold-downs are used at each end of the new cripple walls.
- The reason hold-downs are not required by the other prescriptive standards when retrofitting a house with a continuous foundation, is that the entire wall length can be engaged as part of the resistance to uplift.
- Using a partial perimeter system results in shorter wall lengths and less resistance.
- The hold-downs shown in Elevations D (above) and E in the Appendix must provide at least 2,500 pounds resistance to earthquake loading.
- A variety of products can provide this capacity.
- The drawings depict one type of hold-down that uses bolts through the cripple wall end posts and a bolt embedded in the new foundation.
- Similar hold-downs using special screws instead of bolts may be used if the local building official approves them and they provide an equivalent minimum capacity.
- Other types of hold-downs that use nails to connect to the post may also be used, but typically they require a post height of at least 24 inches.
- In addition, all nailed type hold-downs have limitations on how close they can be placed to the corner of a concrete foundation and some may not be able to provide the minimum required capacity.
- In addition to the hold-down anchor which connects the new posts at each end of the cripple wall to the foundation, a strap shown in Elevation D must be added at each end on the transverse wall sides to tie the new posts to the existing floor framing above.
- This is needed because the transverse walls are parallel to the floor joists and, therefore, do not carry enough dead load to adequately resist the uplift forces.
- The strap completes the load path between the hold-down post and the floor framing so that the floor will not lift off the new cripple wall.