I-beam sagging or rusted under your mobile home

If you are looking for repairs to the I-beam under your mobile home, start here: a sagging I-beam is usually a support problem, not a steel problem. The beam has dropped between piers that are too far apart, have sunk, or are missing, and the fix is to put correct support back under it. That is pier work, typically $75–$150 per pier to reset and $150–$400 per pier to rebuild, from our pricing page.

Rust is the other half of the question. Plenty of frame rust is only on the surface and can be treated. Steel that has rusted through or cracked is a different job, and we tell you straight when that is the case.

What the I-beams do

Every section of a mobile home sits on a steel frame. Federal construction rules describe the frame as the rigid substructure that supports the home both on the road and on its site. In practice that means two long steel beams running the length of each section, with smaller steel outriggers and crossmembers tying them together and reaching out toward the walls. The floor joists sit across the top.

On site, the beams sit on piers. The beam is strong along its length, but it was never meant to span long gaps on its own. That is why the spacing of the piers under it is set by rule:

• Florida’s installation standard, Rule 15C-1.0103, applies when the manufacturer’s instructions do not specify otherwise: piers centered under the I-beam, no more than 8 feet apart, and the first pier within 2 feet of each end of the home. Center-line piers on a multi-section home go at each end of the center line and 8 feet on center.
• The federal standard, 24 CFR 3285.310(c), puts frame piers no more than 24 inches from each end and no more than 120 inches (10 feet) center to center under the main rails. Florida’s 8-foot figure is the tighter of the two.

Your home’s own installation manual comes first if you have it. Either way, a beam with a gap of 12 or 15 feet between piers is carrying load it was not set up for.

Signs to look for

• A visible dip in the beam between two piers, seen from the skirting access with a flashlight.
• A gap between the top of a pier and the bottom of the beam, or a pier you can rock by hand. That pier is carrying nothing.
• Rust scale: flakes that come off in layers, pitting, or a ragged, thinning edge on the bottom flange.
• A beam that bows sideways or twists, rather than running straight.
• Inside the home: sticking doors, sloping floors, and on a doublewide, cracks in the drywall or ceiling running along the marriage line down the middle of the home.

Check this first

From outside, with a flashlight and the skirting access door open:

1. Count the piers along one beam and pace off the length of the home outside. If the math gives you more than about 8 feet between piers, or the end piers are well in from the ends, spacing is a likely cause.
2. Look along the bottom of the beam. A straight beam reads as one clean line. A sag shows as a dip between two piers.
3. Scrape a rusty spot with a screwdriver, but only one you can reach from the opening without crawling in. If it comes off as dust and leaves solid steel, it is surface rust. If it comes off in layers or leaves a pit, note where.
4. Check the clearance. Florida’s standard calls for at least 18 inches between the ground and the bottom of the I-beam. On a sloped lot up to a quarter of the frame may sit lower, but never under 12 inches. Steel sitting close to wet ground rusts faster.
5. Look for leftovers: a bottle jack left in place as a “pier,” stacks of loose wood, or an outrigger that has been cut for ductwork or plumbing.

Do not go under the home, and do not jack it yourself. A home on a single jack is not supported.

What causes it

Piers too far apart. A home can be set with fewer piers than its manual calls for, or lose one later when someone pulls it to get at plumbing or ductwork and never puts it back.

Piers that sank. Sandy ground compacts under a loaded pier pad, and wet weather speeds it up. When one pier drops, the beam spans the gap and its load moves to the neighbors. See pier and pad repair.

Water under the home. A torn underbelly, poor drainage, or a lot that holds water keeps the steel damp. Low clearance makes it worse.

Bad jacking in the past. Lifting on an outrigger or the floor instead of the main beam, or lifting one point too far, can bend steel and crack the home above it.

Cut or missing outriggers and crossmembers. Crossmembers tie the two beams together and outriggers reach out to carry the edges of the floor. Cutting one for a duct or a pipe lets the beam twist and the floor edge drop.

Over-shimmed piers. Tall, loose shim stacks let the beam settle again and again. See leveling done wrong.

The fixes

Welding and sistering: what is fair to expect

Adding steel to a frame, whether that is a welded plate, a section of new beam, or a sister beam alongside the old one, is engineering territory. Federal installation rules (24 CFR 3285.2(c)) say that before an installer supports a home differently from the manufacturer’s instructions, they must first try to get approved designs from the manufacturer, and failing that, an alternate design certified by a registered professional engineer or architect. A frame repair deserves the same treatment.

What is fair to expect from us: we find the damage, measure it, photograph it, and re-support the beam so it is properly carried by piers again. You get those measurements and photos to take to the manufacturer or an engineer. What is not fair to expect from anyone is a quick weld on a beam that is still missing a pier underneath it. Be wary of anyone who offers that.

Pier and leveling work is installation work in Florida, and the law requires a licensed mobile home installer for it. Ask for the licence number of whoever does it, us included. Our installer licence page shows how to check.

When to walk away

There are cases where the honest answer is that the frame is not worth fixing: rust that has gone through the beam in several places, a cracked beam on an older home, or steel so thin it flexes under a jack. A repair designed by an engineer may still be possible, but on an older home the cost can outrun what the home is worth. If we find that, we say so before you spend money on piers or leveling that cannot hold.

Call us

Tell us whether it is a singlewide or a doublewide, roughly how old, what you can see from the skirting access, and whether any doors, floors or ceiling cracks have changed. Photos of the beam and the piers near the sag help a lot. We cover Lakeland and nearby towns including Mulberry, Lake Wales, Bartow and Winter Haven, and the mobile home repair page lists the other work we do under and around the home. Call or use the quote form to set up a look underneath.