Mobile home tie down requirements are decided by two things: the wind zone your home was built for, and the soil it is standing in. Not by a standard number of anchors, and not by what the last installer happened to have on the truck.
That surprises people, because every article on the subject quotes a tidy table of anchor counts. The federal standard does not contain one, and understanding why is what lets you check your own home properly.
The three wind zones
24 CFR 3280.305 establishes them:
| Zone | Design basis | Where |
|---|---|---|
| Zone I | ≥15 psf horizontal wind, ≥9 psf net uplift | Everywhere not listed as II or III |
| Zone II | 100 mph design wind speed, Exposure C | Listed counties in AL, FL, GA, LA, ME, MA, MS, NC, SC, TX, VA |
| Zone III | 110 mph design wind speed | Hawaii, coastal Alaska, US territories, specific FL and LA coastal parishes and counties |
One point of honesty about that table: the regulation gives Zone I as pressure figures, not a wind speed. You will see “under 100 mph” quoted for Zone I all over the internet. That number is not in the CFR text. We are not going to repeat it.
There is also a coastal clause worth knowing. A home not rated for coastal exposure “should not be located within 1500′ of the coastline in Wind Zones II and III, unless the home and its anchoring and foundation system have been designed for the increased requirements specified for Exposure D.”
Your wind zone is on the data plate
The HUD data plate inside the home lists the wind zone, the roof load and the thermal zone the home was designed for — and here is how to find it, the roof load and the thermal zone the home was designed for.
A home built to Zone I cannot simply be installed in a Zone II or III area. The anchoring system in front of you was engineered for the loads on that plate, and moving the home to a windier place does not upgrade it.
If you are buying, this is a five-minute check that can save a home. Find the plate, read the zone, compare it to where the home is standing.
What the standard actually says about mobile home tie down requirements
24 CFR 3285.401 covers anchoring. After the home is blocked and levelled it must be secured by anchor assemblies or an engineered alternative foundation, and the anchoring system must meet the loads shown on the data plate.
Then comes the part that explains the missing table. Installation instructions for anchor assemblies must be prepared by a registered professional engineer or architect, and those instructions are what specify the maximum spacing for diagonal and vertical ties, the minimum and maximum tie angles, how beam rotation is prevented at the attachment points, longitudinal and mating-wall tie-downs, swivel connections and corner protection.
In other words: the numbers exist, but they live in your home’s own installation manual, not in the Code of Federal Regulations. Anyone quoting you “8 feet in Zone I, 6 in Zone II, 4 in Zone III” is quoting a contractor’s rule of thumb, not a federal rule.
The soil test almost nobody knows about
24 CFR 3285.402 requires the soil to be classified by torque probe test at three sample locations:
| Class | Torque probe reading |
|---|---|
| Class 1 | Under 175 in-lb — engineer must be consulted |
| Class 4B | 175–275 in-lb |
| Class 4A | 276–350 in-lb |
| Class 3 | 351–550 in-lb |
| Class 2 | 551 in-lb and above |
And the anchors themselves must be listed or certified to resist an ultimate load of at least 4,725 lb and a working load of at least 3,150 lb — a 1.5 safety factor — installed to full depth, with zinc coating of at least 0.30 oz/ft².
The soil class is what decides which anchor is allowed. Weak soil takes a different anchor, not just more of the same one. If nobody ran a torque probe when your home was set, the anchoring was guessed.
Checking your own
You are looking under the skirting with a torch. Signs that something is wrong:
- Rust or corrosion on straps or anchor heads.
- Slack straps. They should be tight. A strap you can move by hand is doing nothing in a storm.
- Anchors not driven to full depth, or visibly pulled up out of the ground.
- Missing ties where others exist at regular intervals.
- Kinked or bent straps, or straps cutting over a sharp frame edge without corner protection.
- Cracked skirting or an out-of-level home, which often means the ground has moved.
A yearly look, plus a check after any major storm, is what inspectors suggest. That is their recommendation rather than a regulatory requirement.
Frame ties versus over-the-top straps: older single-section homes used straps passing over the roof to handle uplift, and diagonal frame ties replaced them where the manufacturer’s engineered instructions allow. We could not pin the changeover to a date in the CFR text, so treat it as manufacturer- and state-specific rather than a national cut-off.
Insurance, lending and resale
This is where an unanchored home stops being theoretical.
Insurers commonly require tie-down certification before writing a policy, may decline or add exclusions without it, and some give a premium credit for a documented system. FHA and VA financing require engineering certification that the installation meets the HUD standard. Some Florida counties require tie-down certification for permitting.
None of that is uniform. What is uniform is that somebody will ask, at the worst possible moment — when you are selling, insuring or refinancing.
What it costs
Reported figures, from contractor sources rather than any regulation: auger anchors around $45 to $60 each, strap and hardware sets $15 to $25, labour $60 to $85 an hour depending on region, permits $50 to $150, and a soil test or releveling in the $300 to $800 range.
Treat those as typical rather than fixed. There is no federal or state price schedule for this work.
Common questions
How many anchors does my home need?
The number in your home’s installation manual, for your wind zone and soil class. There is no federal figure, and any article that gives you one is guessing.
Can I add anchors myself?
Driving an anchor is not the hard part. Getting the tie angle, the strap tension and the frame attachment right is, and a certification you can hand an insurer needs someone qualified to sign it.
My home is from 1985. Do these rules apply?
The installation standard in 24 CFR 3285 applies to installations under it. An older home was anchored to the rules of its day, which is exactly why an inspection is worth more than an assumption.
What if I cannot find the data plate?
Then you do not know your wind zone, and that is the first problem to solve.