Floor Insulation

The thermal barrier between refrigerated cargo space and vehicle chassis/road surface, consistently specified at half the thickness of roof and wall insulation despite facing equivalent or greater thermal loads. Floor insulation represents the cold chain industry’s most systematic engineering failure—ignored because it’s invisible and challenging to address.

The Radiating Upward Problem

Industry practice for refrigerated vehicle insulation:

• Roof: 75-100mm polyurethane (solar radiation concern)
• Walls: 60-75mm polyurethane
• Floor: 40-50mm polyurethane (often less)

This hierarchy assumes heat primarily enters from above (solar) and sides (ambient air). It ignores the heat source below.

South African pavement in summer sun reaches 55-70°C—20-35°C hotter than ambient air temperature. A vehicle parked on hot asphalt or crawling through traffic sits on a radiating heat source that standard floor insulation cannot adequately resist.

Thermal Load Calculation

Using the Stefan-Boltzmann equation for radiant heat transfer:

For 8m² floor area with:

• Pavement temperature: 60°C (333K)
• Floor external surface: 45°C (318K)
• View factor: 0.5
• Emissivity: 0.9

Radiant heat transfer: ~420W from pavement alone

Add conductive transfer through inadequate insulation:

• 50mm PUR floor, k=0.025 W/m·K
• Temperature differential: 63°C (exterior 45°C to interior -18°C)
• Conductive load: (0.025 × 8 × 63) / 0.05 = 252W

Compare to roof with 75mm insulation and lower temperature differential:

• Solar-heated roof: 55°C
• Interior: -18°C
• Differential: 73°C
• Conductive load: (0.025 × 8 × 73) / 0.075 = 195W

The floor contributes MORE thermal load than the roof, with LESS insulation.

Why Industry Ignores Floor Insulation

1. Cargo height priority: Thicker floors reduce internal height; bodybuilders maximize sellable cargo volume
2. Structural complexity: Floors bear load; adding insulation thickness requires engineering changes
3. Invisible problem: Customers see roof-mounted TRUs and assume that’s where heat enters
4. No accountability: When systems struggle, blame shifts to “hot weather” or “too many stops”

Professional Specification

Proper floor insulation for frozen transport in South African conditions:

• Minimum 75mm polyurethane (matching roof specification)
• Reflective barrier on chassis side (reduce radiant absorption)
• Thermal break at chassis attachment points (prevent conduction bridging)
• Load-bearing surface rated for pallet weights without compression

This specification adds R8,000-12,000 to vehicle build cost and reduces internal height by 25-35mm. It saves R15,000-25,000 in annual fuel costs and prevents countless temperature excursions.

Related Terms: Insulation (Thermal), Urban Heat Island Effect, Thermal Bridge, Thermal Resistance (R-value)

Related Articles: Radiating Upward: The Thermal Load Nobody Calculated (And Why Your Floor Is The Weakest Link)

Related Resources: Technical Formulas Reference (Urban Heat Island Radiant Load calculation)