Use Straps and Diagonal Braces to Increase Strength of Posts
Notes:
- How Should Appendages Connect to Buildings?
- Building appendages are usually connected to the house using nails, lag screws, straps, or braces.
- Nails
- Used to connect the existing house to the building framing [appendage] for resisting gravity loads.
- However, nails may not be a sufficient method of attaching when horizontal forces cause withdrawal (pull out).
- Lag screws
- Used to connect a roof or porch to the house in order to resist lateral earthquake forces.
- Lag screws may attach the ledger to framing of the house.
- Lag screw must be anchored into a stud
- Pilot holes must be drilled to locate the studs
- Straps
- Used when a simple attachment detail is not adequate to hold the porch or roof to the house.
- If length of appendage is more than its width, straps at ends of appendage resist the horizontal swaying of appendage.
- Similar to requirement for hold–downs for shear wall.
- Straps or brackets
- Used to prevent roof overhangs or elevated porches from becoming unstable if they sway too far during earthquake.
- If the swaying is too great, the columns or posts supporting the outside ends will become unstable or detach.
- Posts have little or no attachment to roof or floor deck. Straps or brackets allow the post to move without separating from the roof or floor deck. Note that this does not increase the strength of the post to resist earthquake forces.
- Diagonal braces
- Diagonal braces are only way to increase strength of posts.
- The figure shows correctly installed braces