Mobile Home Inspection: Field Guide for Inspectors

Mobile home inspection throws curveballs that site-built homes don't. If you've spent most of your career inspecting stick-frame construction, your first manufactured home can feel like a different profession. The foundations are different, the framing is different, the electrical standards changed dramatically over the decades, and there are entire systems — tie-downs, marriage lines, belly wraps — that don't exist in conventional housing.

This guide covers what's different, what to check, and how to document it in your report.

HUD Code vs. Building Code: Why It Matters

Manufactured homes built after June 15, 1976 are regulated by the HUD Manufactured Home Construction and Safety Standards — not local building codes. This is a federal standard, and it applies to the original construction.

Homes built before 1976 are technically "mobile homes" under no federal standard. These are the ones that need the most scrutiny and often have the most issues.

For your report: Note the HUD data plate (inside a cabinet or closet) and the HUD certification label(s) on the exterior. If these are missing, document it. The data plate tells you the manufacturer, model, date, wind zone, roof load zone, and thermal zone — all of which inform your inspection.

Foundation and Support Systems

This is the biggest departure from site-built inspection. Manufactured homes sit on pier-and-beam systems, not poured foundations.

Pier Foundations

Most manufactured homes rest on concrete block piers with shimmed bearing points. Check:

• Pier spacing and alignment: Piers should be evenly spaced per the manufacturer's installation manual (typically 6–8 feet on center)
• Concrete block condition: Look for cracked, shifted, or leaning blocks
• Shimming: Wood shims should be tight and not crushed. No more than two shims per stack. Loose shims mean the home has settled or shifted.
• Cap blocks: Each pier should have a solid cap block on top, not open-cell blocks supporting the frame
• Contact with frame: The pier should make full contact with the I-beam. Gaps indicate settlement.
• Footer condition: Piers should sit on concrete footers, not bare soil. In many jurisdictions, footers are required but frequently missing in older installations.

Tie-Downs and Anchoring

Tie-downs resist wind uplift and lateral movement. They're critical in wind zones II and III, but important everywhere.

What to check:

• Straps: Should run over the frame and connect to ground anchors. Look for rust, fraying, or slack.
• Ground anchors: Typically auger-type anchors driven into soil. Verify they're present and haven't pulled.
• Strap spacing: Usually every 6–8 feet along the frame. Count them and note gaps.
• Frame anchors vs. over-the-top straps: Some installations use both. Document what's present.
• Corrosion: Steel straps in humid climates deteriorate. Surface rust is one thing; structural rust is another.

Document it as: "Tie-down system observed with [number] straps at approximately [spacing]. [Condition notes]. Recommend review by manufactured home installer if deficiencies noted."

Skirting

Skirting isn't structural, but it affects pest intrusion, moisture control, and plumbing freeze risk.

• Check for adequate ventilation openings (1 sq ft per 150 sq ft of under-home area, or 1:1500 with vapor barrier)
• Look for damage, gaps, or missing sections
• Note the material: vinyl, metal, concrete block, or lattice

The Marriage Line

Double-wide and multi-section homes are joined at the "marriage line" — the seam where factory-built halves meet. This is one of the most inspection-critical areas.

Exterior Marriage Line

• Roof: Look for ridge cap separation, misaligned shingles, or flashing failure at the seam
• Walls: Check for gaps, caulk failure, or visible separation at the exterior joint
• Floor level: Sight down the marriage line — if one half is higher than the other, the foundation has shifted

Interior Marriage Line

• Ceiling: Run your eye along the center ceiling line. Cracks, tape failure, or bowing indicate movement.
• Floor: Walk the marriage line slowly. Unevenness, squeaking, or soft spots suggest poor joining or foundation settlement.
• Walls: Check for drywall cracks or panel separation at the center wall

This is where voice documentation shines. Walking the marriage line and dictating observations — "ceiling seam showing 3/8 inch separation at master bedroom, floor drops approximately half inch at hallway transition" — is dramatically faster than stopping to type. Tools like ReportWalk let you narrate as you walk and get structured report text back.

Electrical Systems: The Aluminum Wiring Question

Manufactured homes from the 1960s through the mid-1970s frequently have aluminum branch circuit wiring. Post-HUD homes (after 1976) mostly use copper, but not always.

What to Check

• Panel: Open the main panel. Note wire color (silver = aluminum, copper = copper). Check for signs of overheating at breaker connections.
• Outlets and switches: If accessible, check connections for oxidation, discoloration, or overheating evidence
• Federal Pacific and Zinsco panels: Common in this era and a known safety issue. Document and recommend evaluation by a licensed electrician.
• Wiring gauge: Manufactured homes often used smaller gauge wiring than site-built homes of the same era. Note what you observe.
• Grounding: Check for proper grounding at the panel and at the service entrance. Manufactured homes should be grounded to a driven ground rod.

Document it as: "Aluminum branch circuit wiring observed. Connections should be evaluated by a licensed electrician. Recommend COPALUM or AlumiConn connectors at all connection points if not already present."

For more on documenting electrical findings, see our electrical inspection checklist.

Plumbing: Under-Home Access and Freeze Protection

Manufactured home plumbing runs through the floor system and underneath the home — not through walls and basement like site-built construction.

Key Inspection Points

• Supply lines: Often polybutylene (PB) in 1980s–1990s homes. Gray, blue, or black flexible pipe with acetal (plastic) fittings. Document PB pipe if found — it's a known failure-prone material.
• Drain lines: Check under the home for proper slope, hangers, and connections. Belly sag in drain lines is common and causes chronic drainage issues.
• Water heater: Usually in a closet or utility space. Check for proper venting (gas units) and TPR valve discharge routing.
• Freeze protection: Heat tape on supply lines is common in cold climates. Check that it's present and functional if applicable.
• Belly wrap integrity: Damaged belly wrap (the plastic membrane underneath the home) exposes plumbing to freezing temps and pests.

The Belly Wrap and Vapor Barrier

The bottom board — commonly called the belly wrap — is the membrane that seals the underside of the manufactured home. It serves as a vapor barrier, pest barrier, and insulation retainer.

What to check:

• Tears, holes, and sagging: Animals, moisture, and age damage the belly wrap. Sagging sections may indicate insulation falling or water accumulation.
• Repairs: Tape patches are common but often fail. Note the quality of any repairs.
• Moisture: Wet or stained belly wrap suggests plumbing leaks or condensation issues. Probe for soft spots.
• Pest intrusion: Rodents and insects enter through damaged belly wrap. Look for droppings, nesting material, or damage patterns.

You'll need a good flashlight and possibly a creeper to inspect under a manufactured home. If the crawl height is less than 18 inches, note that access was limited and document what you could observe from the perimeter.

For crawl space techniques that apply here, see our crawl space inspection guide.

HVAC in Manufactured Homes

Heating and cooling in manufactured homes has some unique characteristics:

• Ductwork: Often runs under the floor in the belly cavity. Disconnected or crushed ducts are common — especially at crossover ducts (the flexible duct connecting sections at the marriage line in double-wides).
• Furnace: Typically a downflow or horizontal unit. Check combustion air supply — manufactured homes are tight and need adequate combustion air.
• Crossover duct: This flexible duct connects HVAC between sections in multi-section homes. It's exposed under the home and frequently damaged. Check for disconnection, crushing, or deterioration.

Roof Systems

Manufactured home roofs are typically either:

• Flat/low-slope (older homes): Metal roof with slight pitch. Check for rust, seam failure, and ponding.
• Pitched/shingled (newer homes): Truss roof that looks like site-built. Inspect like any shingled roof but pay special attention to the marriage line ridge.

Regardless of type, check:

• Roof-over situations (new roof installed over old roof) — adds weight and can hide damage
• Ceiling panels for water staining
• Attic access if available (many manufactured homes have limited or no attic access)

Report Sections Unique to Mobile Homes

Your manufactured home report should include sections that don't appear in a standard site-built report:

1. HUD Data Plate and Labels — Present/absent, information noted
2. Foundation/Pier System — Pier condition, spacing, footers, settlement
3. Tie-Down/Anchoring System — Strap condition, anchor condition, spacing
4. Marriage Line (multi-section) — Interior and exterior condition
5. Belly Wrap/Bottom Board — Condition, damage, moisture
6. Skirting — Condition, ventilation
7. Crossover Duct (multi-section) — Condition, connection

These sections set your manufactured home reports apart and demonstrate expertise to your clients. If you're building report templates, having a dedicated manufactured home template saves significant time.

Pricing Your Mobile Home Inspections

Mobile home inspections often take similar time to site-built inspections but inspectors sometimes undercharge. The under-home inspection is physically demanding, the systems are unique, and the liability exposure is real. Price accordingly — see our home inspection pricing guide for strategy on setting and justifying your rates.

Speed Up Your Manufactured Home Reports

Manufactured home inspections involve a lot of crawling, climbing, and awkward positions — exactly the situations where typing on a phone or tablet is slowest. Voice-based documentation tools let you dictate findings while you're under the home, at the marriage line, or on the roof.

ReportWalk turns your voice notes into structured inspection report narratives — no templates to click through, no tiny checkboxes. Just say what you see and get a professional report back. Try ReportWalk free →