Most Los Angeles houses built before the 1980s were never tied down. The framing sits on a mudsill, the mudsill sits on the foundation, and nothing meaningful connects the two. In a shake, that is the joint that lets a house slide off its stem wall or a cripple wall fold over. Seismic retrofit hardware exists to close that gap — and the three families that do the work are holdowns, straps, and anchor bolts. Here is what each one resists, where it goes, and how to buy it.
What a retrofit is actually trying to stop
Two failure modes, two different fixes. Sliding is the house moving sideways off the foundation; you stop it with anchor bolts through the mudsill and with sheathing on the cripple walls. Overturning is the end of a shearwall trying to lift as the wall racks; you stop it with a holdown or a strap that ties the post down to the concrete or to the framing below.
Get the distinction right and the shopping list writes itself. Bolts and plate washers resist shear. Holdowns and straps resist tension. A retrofit that only adds bolts leaves the uplift path open, and a retrofit that only adds holdowns leaves the house free to slide. Nearly every LADBS-approved soft-story and foundation-bolting scheme includes both.
Holdowns: the tension anchor at the end of a shearwall
A holdown is a heavy steel bracket that bolts to a post and to an anchor embedded in the concrete. When the wall tries to rotate, the holdown carries that uplift straight into the foundation. Our Holdowns collection carries the Simpson Strong-Tie families you will see called out on LA plan sets.
The HDU series is the workhorse. The HDU2 holdown is 14-gauge, G90 galvanized, 8-11/16 in. tall, and installs with a 5/8 in. diameter anchor bolt plus 1/4 in. x 2-1/2 in. Strong-Drive SDS Heavy-Duty screws. The seat is predeflected at the factory, which matters more than it sounds: material stretch under load is what lets a wall move before the hardware engages, and predeflection removes most of it. Step up to the HDUE9 — 10-gauge, 17-5/16 in., 7/8 in. anchor bolt — where the engineer calls for more capacity.
The screws matter as much as the bracket. HDU holdowns use SDS Heavy-Duty Connector screws rather than through-bolts because screws reduce fastener slip and leave more net section in the post. Some SKUs ship with the screws included; the HDUE7, for example, calls for thirteen 1/4 in. x 3 in. screws that are not in the box. Check that line on the product page before the crew shows up.
Strap-tie holdowns for new concrete
When you are pouring rather than retrofitting, an embedded strap-tie holdown is simpler. The STHD10 strap-tie holdown is 12-gauge, 24-5/8 in. long, and sets into the wet pour; slots below the embedment line improve the concrete bond and reduce spalling, and the staggered nail pattern limits splitting in the post. It nails off with 0.148 in. x 3-1/4 in. nails. For the highest loads, the bolted HD19 is self-jigging so the code-required seven-bolt-diameter edge distance is met when it sits flush on the sill.
Straps: continuous tension ties through the framing
Straps carry tension where a bracket will not fit — floor-to-floor uplift, roof uplift, and horizontal ties across a diaphragm. Coiled strap is the practical form: you buy a roll and cut to length on site, which is cheaper than stocking a dozen pre-cut sizes.
The CS16-R coiled strap is 16-gauge, G90 galvanized, sized for nominal 2x lumber, and installs with 8d or 10d common nails. For heavier work the CMST12 strap is 12-gauge and designed for double 2x stud or post applications, specifically for shearwall overturning and roof uplift. Browse the full Coiled Straps collection for gauges from 22 up to 12.
Two field rules. Fill every hole the load path needs — a strap at half its nailing schedule carries roughly half its rating, and inspectors count nails. And keep the strap straight; a strap bent around a corner or over a rim joist is no longer working in pure tension. Our guide to why metal straps matter in LA construction covers the general strap and plate families beyond the coiled products.
Anchor bolts: the shear connection to the foundation
Foundation bolts are what stop the house sliding. On an existing home the retrofit version is usually an epoxy-set or expansion anchor drilled through the mudsill into the stem wall; on new work the bolts are cast into the wet pour. Our 1/2 in. x 12 in. galvanized foundation bolts come in 50-packs for bolting a full perimeter, and the 5/8 in. x 12 in. version with a square plate washer covers the heavier spec.
The plate washer is not optional and it is the detail most commonly missed on DIY retrofits. A round cut washer lets the sill plate split and pull over the bolt; the square plate washer spreads the load into the wood and is what the code-approved plans show. Buy the bolt and the washer together.
Drilling into a 1930s stem wall is its own problem — aggregate, rebar, and limited headroom under a floor. Our guide to drill bit types covers what belongs in a rotary hammer for that work, and the concrete anchors comparison explains when a wedge, sleeve, or screw anchor is the right retrofit fastener.
Hardware at a glance
| Hardware |
Resists |
Installs Into |
Typical Use |
| Holdown (HDU) |
Uplift, overturning |
Post plus anchor bolt |
Shearwall ends |
| Strap-tie (STHD) |
Uplift, overturning |
Wet concrete pour |
New foundations |
| Coiled strap |
Tension, uplift |
2x studs and posts |
Floor-to-floor ties |
| Foundation bolt |
Sliding shear |
Concrete stem wall |
Mudsill bolting |
Corrosion and the LA environment
Every connector above ships G90 galvanized, and that is the right minimum for a crawlspace. Two conditions call for more. Coastal homes from the South Bay to Malibu see salt air even under the floor, and treated lumber — common in sill plates and any wood in contact with concrete — carries copper-based preservatives that attack plain and lightly coated steel. Where plans allow, step up the coating rather than discovering rust at the next inspection.
Mixing metals is the other quiet failure. Match the fastener finish to the connector finish; a bright screw in a galvanized holdown corrodes first and takes the connection with it. Manufacturers publish which fasteners are approved for each connector, and the load rating is only valid with those fasteners.
Buying for a permitted retrofit in Los Angeles
Soft-story and foundation-bolting retrofits in LA run on approved plan sets, and those plans name the hardware by model number. That is the shopping list — not a lookalike with a similar capacity. Substituting a different bracket, a different bolt diameter, or a different fastener voids the tested load value, and LADBS inspectors check the callouts.
Order the connectors, the fasteners, and the anchors together so nothing stops the crew mid-wall. The Wood Connectors collection carries the brackets and angles that go with these assemblies, and our bolt types guide explains where a machine bolt is required and a lag is not acceptable. We deliver across Los Angeles County, and we can pull a full hardware list from your plan sheet if you send it over.
Frequently asked questions
Do I need a permit for a seismic retrofit?
Yes. Foundation bolting and cripple-wall bracing are permitted work in the City of Los Angeles, and mandatory soft-story retrofits follow an ordinance-driven process with engineered plans. The permit is also what makes the work count for insurance and disclosure purposes.
Can I install holdowns myself?
The physical work is within reach of an experienced builder, but the hardware selection is not a judgment call — it comes from an engineer's plan. Buying and installing a holdown that was not specified for your wall gives you hardware without a verified load path.
What is the difference between a holdown and a strap?
Both resist tension. A holdown is a bracket that transfers uplift from a post into an anchor bolt in concrete; a strap is a flat steel tie that carries tension between framing members, typically across floors. Many retrofits use both in the same load path.
Do coiled straps need a specific nail?
Yes. Each strap lists its fastener — commonly 8d or 10d common nails for CS products, and 0.148 in. x 3-1/4 in. nails for heavier straps and strap-tie holdowns. Sinkers, box nails, and screws are not interchangeable with common nails unless the manufacturer lists them.
Does a retrofit have to be done all at once?
Structurally, a partial load path is a weak load path, so plans are drawn as a complete system. That said, work is often phased by area of the crawlspace. Follow the sequence on your approved plans rather than picking the easiest sections first.
