Mobile Home I-Beam Measurement — Sizes, Specs & Frame Guide
The steel I-beam frame is the structural backbone of every manufactured home. When you're planning a move, evaluating damage, replacing a section, or getting a home set on a new foundation, knowing the exact I-beam dimensions matters. This guide gives you the actual measurements, standard sizes by home type, how to measure your own frame, and what beam damage looks like before it becomes a crisis.
The steel I-beam frame of a manufactured home — the main beams run the full length of the home, with outriggers extending to each side.
What the Mobile Home I-Beam Frame Is
Every manufactured home sits on a welded steel chassis made up of I-shaped steel beams. The name comes from the cross-section profile — when you look at the end of the beam, it looks like a capital letter "I." The top and bottom flat sections are called flanges. The vertical section connecting them is called the web.
Unlike site-built homes that sit on a concrete foundation, manufactured homes are built on this steel frame. The frame travels with the home when it's moved, serves as the mounting point for the axles during transport, and connects to the blocking or piers when the home is set on its permanent site.
According to the U.S. Department of Housing and Urban Development (HUD), manufactured home chassis must meet federal construction and safety standards — including specific requirements for frame steel grade, weld quality, and structural load capacity. These standards have been in place since 1976 and define the minimum frame specifications for all new manufactured homes.
I-Beam anatomy — the measurement you need is web height × flange width
Standard I-Beam Sizes by Home Type
Mobile home I-beams are specified by their web height first, then flange width. A "6-inch I-beam" has a 6-inch tall web. The flange width and steel thickness vary by manufacturer and era of construction, but the table below reflects the standard dimensions found in the vast majority of manufactured homes.
| Home Type | Typical I-Beam Size | Web Height | Flange Width | Weight (lbs/ft) |
|---|---|---|---|---|
| Light single-wide (older) | 6-inch I-beam | 6" | 2" – 2.5" | ~8–10 lbs/ft |
| Standard single-wide | 8-inch I-beam | 8" | 2.5" – 3" | ~11–13 lbs/ft |
| Heavy single-wide / light double-wide | 10-inch I-beam | 10" | 3" – 3.5" | ~15–17 lbs/ft |
| Standard double-wide | 12-inch I-beam | 12" | 3.5" – 4" | ~19–22 lbs/ft |
| Triple-wide / heavy double-wide | 14-inch I-beam | 14" | 4" – 5" | ~22–26 lbs/ft |
These are industry standard ranges — your specific home may vary. Older homes from the 1960s and 1970s sometimes used lighter frames than current standards require. The only accurate way to know your beam size is to measure it directly. See the measuring section below.
How to Measure Your I-Beam
Measure web height from the top of the bottom flange to the bottom of the top flange.
You'll need a tape measure and access to the underside of the home — either by pulling back the skirting and reaching under, or from a crawl space if you have one. The belly board (insulated underbelly) may need to be partially opened to get accurate access in some areas.
Three Key Measurements
1. Web Height — Measure the vertical distance from the top of the bottom flange to the bottom of the top flange. This is the primary beam designation — a beam measuring 8 inches here is an "8-inch I-beam." Do not include the flange thickness in this measurement.
2. Flange Width — Measure the horizontal width of either the top or bottom flange. Both flanges should be the same width. This tells you the beam's lateral bearing surface.
3. Overall Depth — The total height of the beam including both flanges. This is the web height plus the thickness of both flanges. A typical 8-inch beam has an overall depth of approximately 8.5–9 inches when flange thickness is included.
Measure the I-beam in at least three locations along its length — at each end and in the middle. Beams on older homes can develop a bow or camber over time, and measuring in multiple spots helps you identify any deflection that may indicate a problem. A perfectly straight beam should read the same depth at every point.
Frame Dimensions — Chassis Length and Outriggers
Main Beams
Every manufactured home chassis has two main I-beams running the full length of the home, parallel to each other. On a single-wide, these beams are typically spaced 36–48 inches apart measured center-to-center. On a double-wide, each section has its own pair of main beams that bolt together at the marriage wall.
Outriggers
Perpendicular to the main beams are smaller cross-members called outriggers. These extend from the main beams outward to the edges of the home's floor platform. Outrigger spacing is typically 16 or 24 inches on center — matching the wall stud spacing above them. Standard outrigger sections are smaller C-channel or I-beam steel, typically 3–4 inches in depth.
Frame Length vs. Home Length
The frame length is slightly shorter than the overall home length because the home's body overhangs the chassis at both ends, typically by 12–24 inches. When you're sizing a new frame for a replacement or transport, use the frame length — not the overall home length — for beam length calculations. Measure from the front crossmember to the rear crossmember for the actual frame dimension.
| Home Width | Main Beam Spacing (approx.) | Typical Frame Width |
|---|---|---|
| Single-wide (14' wide) | 36" – 42" center-to-center | Frame width ≈ 10'–11' |
| Single-wide (16' wide) | 42" – 48" center-to-center | Frame width ≈ 11'–12' |
| Double-wide (24' wide) | Two separate sections, each ≈ 36"–42" beam spacing | Each section frame ≈ 10'–11' |
| Double-wide (28' wide) | Two separate sections, each ≈ 42"–48" beam spacing | Each section frame ≈ 12' |
I-Beams and Foundation Types
A double-wide set on a foundation — the I-beam frame rests on concrete piers or perimeter blocks.
When a manufactured home is set on its site, the I-beam frame is the primary load transfer point. Concrete piers, adjustable steel piers, or perimeter block walls contact the bottom flange of the main I-beams and transfer the home's weight to the ground.
This is why I-beam measurement matters for foundation work: pier placement must align with the main beams — not the outriggers — for proper structural support. A pier under an outrigger rather than a main beam can crack or deflect the outrigger over time without providing adequate support.
For complete foundation type details, blocking specifications, and HUD pier spacing requirements, see the related articles at the bottom of this page.
Signs of I-Beam Damage
I-beam frame damage is often invisible from inside the home until it's significant. The most common causes are corrosion from persistent moisture under the belly, impact damage during transport, and overloading from improper blocking that puts point loads on the web rather than the flanges.
🦀 Surface Rust
Light surface rust on the frame is normal and not structurally significant. Treat with a rust converter and paint. Red rust that's pitting or flaking away from the flange surface needs professional assessment — the cross-section is being reduced.
🌊 Web Buckling
The vertical web section is the most vulnerable to buckling under point loads. A buckled or kinked web significantly reduces the beam's load capacity and is typically a replacement rather than repair situation.
📐 Frame Deflection (Camber)
A beam that sags or bows along its length indicates overloading or long-term stress. Check by snapping a chalk line along the bottom flange — any visible dip or rise indicates deflection that needs evaluation.
🔩 Weld Failures
Cracks at weld points — especially where outriggers meet main beams or at the hitch connection point — are serious. These are high-stress locations and cracked welds can propagate quickly. Do not move a home with cracked chassis welds.
Replacing a section of main I-beam in a manufactured home requires lifting the entire home off its frame, removing the damaged section, welding in new steel, and resetting the home. This typically costs $5,000–$15,000 depending on the extent of damage and access. For an older home worth $20,000–$30,000, this repair is often economically questionable. Get a cash offer before committing to a major frame repair.
Frequently Asked Questions
What size I-beam does a mobile home use?
Standard single-wide manufactured homes typically use 8-inch I-beams. Older or lighter single-wides may use 6-inch beams. Double-wides generally use 10-inch or 12-inch beams. The exact size depends on the home's age, manufacturer, and width — measure directly for confirmation.
How do I measure a mobile home I-beam?
Access the frame from under the home by pulling back the skirting. Measure the web height — the distance from the top of the bottom flange to the bottom of the top flange — with a tape measure. This gives you the beam designation (6", 8", 10", etc.). Also measure flange width and overall depth for a complete picture.
How far apart are the main I-beams on a mobile home?
On most single-wide manufactured homes, the two main I-beams are spaced 36–48 inches apart measured center-to-center. Wider homes have wider spacing. The exact spacing matters for pier placement — piers must sit under the main beams, not the outriggers between them.
Can a mobile home I-beam be repaired or does it need replacement?
Surface rust can be treated and doesn't require replacement. Significant section loss from deep rust, buckled webs, or cracked welds typically require professional welding repair or section replacement. Any frame repair on a manufactured home should be assessed and performed by a qualified structural welder familiar with mobile home construction — DIY welding on a structural chassis is not recommended.
What is the difference between the main I-beams and outriggers?
The main I-beams run the full length of the home and carry all structural loads. Outriggers are smaller perpendicular cross-members that span between the main beams and extend to the edges of the home's floor platform. Piers and blocking should contact the main beams — not the outriggers — for proper load transfer.
Related Articles
More mobile home structural guides:
I-Beam Repairs Can Cost More Than the Home
A major frame repair — buckled web, cracked welds, significant rust — on an older single-wide can easily run $5,000–$15,000. On a home worth $15,000–$25,000, that math doesn't work. Before committing to a structural repair, find out what a cash buyer would pay as-is. We buy manufactured homes with frame issues and close in 7 days.
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