Why A23, A34, L30 and Similar Clips Are Not Proper Post Connections in Bay Area Seismic Retrofits
In Bay Area crawl spaces, we keep seeing the same pattern:
- Concrete piers with little 2×6 “pier blocks” on top
- A wood post sitting on that block
- A couple of A23, A34, L30, or generic L‑angles nailed between the post and that 2×6 and/ or the post and the beam
To homeowners and inspectors, it looks like “nice hardware – better than nothing.”
In reality, it often does almost nothing for seismic performance, and it can create a false sense of security that is more dangerous than knowing you still have a problem.
This article explains why these improvised connections are not a substitute for real post bases, post caps, and anchored connections, and why you should insist on the right hardware and detailing in a high seismic zone like the Bay Area.
If you want a professional opinion on what’s already under your house, start here:
Seismic, Foundation & Drainage Services
1. Improvised Angles Are Not Engineered Post Connections
We routinely see the following used between posts and beams or posts and pier‑blocks:
- Simpson A23 angles
- Simpson A34 framing angles
- Simpson L30 angles
- Miscellaneous generic angles or clips
These are good products when used for the purposes they were designed and tested for:
- Small framing forces in walls or roofs
- Light brackets and trim conditions
- Miscellaneous blocking and bracing
They were not designed as primary post‑to‑beam or post‑to‑foundation connectors in high‑seismic applications.
Simpson Strong‑Tie publishes for each connector:
- Approved applications
- Allowable loads
- Required fasteners
- Installation diagrams
If you use a connector outside those published applications, the published load values no longer apply. An A23 nailed into a 2×6 pier block or beam is not magically equivalent to a proper post cap/base that has been specifically engineered and tested for that job.
For proper post connections, Simpson and others already make hardware such as:
- AC / ACHZ type post caps (post‑to‑beam)
- ABA / ABU type post bases (post‑to‑concrete)
These have known capacities for gravity, uplift, and lateral forces when installed as specified. A couple of light angles chosen because they “fit” is not the same thing.
2. Connecting to a 2×6 Pier Block Is Not Connecting to the Pier
In many older Bay Area homes, the stacked assembly at a crawl‑space pier looks like this:
soil → concrete pier → little wood block (often a 2×6) → wood post → beam
Some contractors install angles that connect:
- Post → 2×6 block
but not:
- Post → actual concrete pier or foundation
That means:
- You have a connection between two pieces of wood
- You do not have a positive connection into the concrete support
During an earthquake, the load path is supposed to be:
floor framing → beam → post → concrete pier/footing → soil
If the metal only grabs the post and the loose 2×6 sitting on top, you still have a disconnected pier. The weakest link is unchanged: the post can still walk, slide, or jump off the pier.
3. What the Code Actually Expects at Posts
The residential codes are very clear that posts can’t just be “sitting there.”
Columns must be restrained at the bottom
IRC/CRC R407.3 (for structural columns) requires that columns be restrained to prevent lateral displacement at the bottom. That means:
- There needs to be a positive mechanical connection between the bottom of the post and the foundation that actually prevents sideways movement. Simply resting the post on, or screwing it to, a small wood block sitting on top of the pier does not provide that lateral restraint, even if the block itself is partially embedded or tight‑fitting.
Angles nailed into a pier block that is just resting on the pier generally do not provide that restraint. The entire wood‑on‑concrete interface can still slide.
Deck post analogy
For decks, the code requires:
- Posts sitting on footings with mechanical connectors that restrain lateral movement
The same physics apply in a crawl space:
- A post that is not positively anchored to the pier is still vulnerable to sliding and overturning in an earthquake.
4. “Better Than Nothing” Can Be Worse Than Nothing
The biggest danger with these “upgrade” angles is not just that they’re weak. It’s that they look strong:
- Shiny steel hardware
- Many nails
To a homeowner, it reads as “professionally reinforced.” To many inspectors, on a quick voluntary retrofit inspection, it reads as “looks OK; at least they did something.”
But if the connector:
- Was never engineered for that application
- Is attached only to a loose wood block instead of the pier
- Has unknown uplift or lateral capacity
…then you still have the same failure mode: a post that is not properly tied into the foundation.
Believing a problem is solved when it isn’t is worse than knowing you still need work. People make decisions about insurance, occupancy, and risk based on that belief.
5. Why Contractors Use the Wrong Hardware
From what we see in the field, common reasons include:
- No formal retrofit training. California does not require a seismic‑specific license or certification to advertise seismic retrofit services.
- “Use what’s on the truck.” If all they carry are generic angles, that’s what gets installed.
- Homeowners can’t tell the difference. A clip is a clip to the untrained eye.
- Limited inspection bandwidth. Inspectors are checking for general code compliance on short visits. On voluntary retrofits, especially, there’s rarely time to check every connection.
None of these excuses change the engineering:
- The connection should be selected because it is designed, tested, and approved for that exact job, not because it happened to be in the toolbox.
6. What Proper Post Connections Look Like in a Bay Area Retrofit
For a raised‑foundation home in a high seismic zone, we want:
- Embedded, properly sized concrete piers or continuous foundations where needed
- Anchored post bases that tie the wood post into the concrete (drilled/epoxied or cast‑in anchors)
- Properly sized wood posts (4x, 6x, etc., as designed)
- Post caps or other listed connectors that tie posts into beams or girder framing
- A continuous load path from floor framing all the way into the footing and soil
We detail and build these connections every week as part of:
- Crawl Space & Cripple Wall Retrofits
- Foundation Repair & Replacement
- Basement Retrofits & Conversions
If you’d like a deeper structural explanation of how that load path should work, this guide helps:
Beyond Foundation Bolts: The California Seismic Load Path Guide for Bay Area Homes
7. How to Tell if Your Posts Are Properly Connected
If you can safely see your crawl space or basement supports, look for:
- Does the post connect directly to concrete with a real post base?
- Is there a loose wood block between the post and the pier?
- Are the only connectors small L‑angles into that wood block?
- Is there any visible anchor or bolt into the pier itself?
If the answer is:
- “Angles just between post and 2×6, nothing into the pier,”
then you probably do not have a fully developed connection into the foundation.
If your home is advertised as “retrofitted” and you’re seeing improvised hardware like this, it may be worth a closer look. Our Seismic Truth Audit™ exists exactly to document these kinds of issues in existing work.
8. What To Do If You Suspect Improper Post Hardware
If you’re in the Greater San Francisco Bay Area and think your posts or piers were “upgraded” with questionable clips:
- Document what you see (photos of posts, piers, and hardware).
- Get an independent evaluation – not from the contractor who installed it.
- If needed, involve a structural engineer to confirm the required hardware and detailing.
- Plan corrections around proper embedded piers and listed post bases/caps, not more improvised angles.
You can learn more about what lives under most Bay Area houses here:
Under Your Home: The Bay Area Crawl‑Space & Foundation Guide
9. The Bottom Line
- A23s, A34s, L30s and similar angles are good connectors when used as designed.
- They are not a proper substitute for engineered post caps and post bases in Bay Area seismic retrofits.
- Connecting a post only to a loose 2×6 pier block on top of a pier does not create a real connection to the foundation.
- “Better than nothing” can be worse than nothing if it convinces you a critical weakness has been solved when it hasn’t.
When manufacturers already provide post caps, post bases, anchors, and tested details specifically for supporting posts in high‑seismic conditions, there is very little justification for making up a connection out of miscellaneous angles.
If you want a second opinion on the hardware under your home – or on a retrofit proposal you’re being sold – we can crawl it, photograph it, and tell you honestly what you have and what you need.
Seismic, Foundation & Drainage Services
