As park home residents search for ways to eliminate freezing floors and lower energy bills, they are met with a dizzying range of insulation products. From multi-foil drapes and mineral wool rolls to rigid PIR boards and expanding spray foam, choosing the wrong material can lead to costly mistakes.

Underneath a park home, environmental conditions are uniquely challenging. Soil moisture, subfloor air movement, and steel chassis flex mean that standard house insulation methods often fail—or worse, cause structural decay.

This guide evaluates the four main insulation types and explains why rigid foil-faced insulation remains the gold standard for park home retrofits.

Evaluating Park Home Insulation Materials

1. Rigid Foil-Faced PIR Board (The Gold Standard)

High-density Polyisocyanurate (PIR) boards with reflective aluminum foil facings are engineered for high thermal performance in thin profiles.

• Pros: Exceptional insulation value ($R$-value per inch), complete resistance to sagging, reflects radiant heat back into floorboards, and leaves joists inspectable.
• Cons: Requires precise hand-cutting between joist spans to ensure zero perimeter air gaps.

2. Multi-Foil Layered Quilts

Multi-foil consists of alternating layers of reflective foil and thermo-wadding.

• Pros: Highly flexible, light, and acts as an effective vapor seal when fully taped at join seams.
• Cons: Must be properly tensioned and stapled; if allowed to droop, air currents can compromise its thermal effectiveness.

3. Mineral Wool / Glass Fibre Rolls (Avoid Underfloor Use)

Traditional loft insulation rolls laid underneath floorboards.

• Pros: Inexpensive upfront material cost.
• Cons: Highly hygroscopic (absorbs moisture like a sponge). Ground humidity causes it to become heavy, sag away from floorboards, and trap water directly against timber joists, accelerating rot.

The Danger: Why Expanding Spray Foam Should Be Avoided

In recent years, expanding spray foam (both open-cell and closed-cell) has been heavily marketed to homeowners. While it creates a tight seal, applying spray foam directly to the underside of a park home carries severe risks:

[ Expanding Spray Foam Applied to Subfloor ]
                   │
                   ▼
┌───────────────────────────────────────────────────────────┐
│     1. TIMBER JOISTS & FLOOR DECK COMPLETELY ENCASED       │
│ Traps existing moisture; prevents wood from "breathing"   │
└───────────────────────────┬───────────────────────────────┘
                   │
                   ▼
┌───────────────────────────────────────────────────────────┐
│     2. HIDDEN WET ROT & STRUCTURAL DECAY                  │
│ Joists decay out of sight; repairs require foam scraping  │
└───────────────────────────┬───────────────────────────────┘
                   │
                   ▼
┌───────────────────────────────────────────────────────────┐
│     3. INSURANCE & VALUATION COMPLICATIONS                │
│ Insurers and surveyors flag uninspectable timber spaces   │
└───────────────────────────┴───────────────────────────────┘

Why Spray Foam Causes Severe Issues:

• Conceals Timber Structure: Spray foam encases joists and floorboards in a thick, rigid shell. Building surveyors cannot inspect timber condition, check for moisture levels, or spot early signs of dry rot.
• Traps Moisture Against Floorboards: If ground vapor or an internal plumbing leak reaches the foam, water becomes trapped against the wood deck. Because air cannot circulate over the timber, wet rot sets in rapidly.
• Covers Pipework & Wiring: Electrical cables and plumbing runs sprayed over with expanding foam become inaccessible, making basic repairs or re-wiring impossible without costly foam removal.
• Insurance & Resale Red Flags: A growing number of UK park home insurance providers and surveyors flag spray foam as a hazard due to concealed timber risks. This can lead to declined coverage or complications during resale.

What to Look for in a Professional Retrofit

A safe, long-lasting underfloor insulation system should deliver three non-negotiable features:

1. Maintain Breathability & Accessibility: Timber joists must remain visible from underneath for future inspections and maintenance.
2. Include Vapor Barrier Protection: A heavy-duty ground membrane should prevent earth moisture from rising, combined with sealed thermal panels.
3. Preserve Subfloor Ventilation: Airflow through skirting vents must remain clear to prevent stale air pockets under your living spaces.

Want Safe, Professional Underfloor Insulation for Your Park Home?

Protect your home structure and enjoy warm floors with our engineered rigid foil systems. Call our specialist team today on 0800 303 2040 to book a Free Subfloor Inspection & Quotation.