The answer is: it depends on the insulation. Modular home manufacturers typically distinguish between two versions: seasonal (PIR 50 mm) and year-round (PIR 75–100 mm or more). The difference is not only in heating costs, but also in living comfort and the durability of the structure.
PIR (polyisocyanurate) is a rigid insulating foam with a very low thermal conductivity coefficient (λ ≈ 0.022 W/mK). For comparison: mineral wool is λ ≈ 0.035, EPS polystyrene ≈ 0.040. This means that 50 mm of PIR insulates as well as roughly 80 mm of wool.
In modular homes, PIR is the standard because: (1) it is lightweight (transport, crane), (2) thin (does not eat into usable floor space), (3) hydrophobic (does not absorb moisture), (4) self-extinguishing (fire safety).
| PIR thickness | U (W/m²K) | Season | Heating | Upgrade for 38 m² |
|---|---|---|---|---|
| 50 mm (standard) | ≈ 0.44 | Spring–autumn, +5°C | Space heater or AC | €0 (included) |
| 75 mm | ≈ 0.29 | All year, -10°C | Electric radiators + ventilation | +€1,100 |
| 100 mm (year-round) | ≈ 0.22 | Full year, -20°C | Heat pump + heat-recovery ventilation | +€2,200 |
| 150 mm (passive) | ≈ 0.15 | Energy class A | Minimal (passive class) | +€4,000 |
PIR 50 mm is entirely sufficient. Cool in summer, and in spring and autumn you can heat it to +18°C with AC or a space heater. In winter — you don't use it. This is the cheapest option.
We recommend PIR 75 mm. You extend the season through all of October and March, while heating costs from November to February remain acceptable. The upgrade pays back within 1–2 seasons.
PIR 100 mm minimum, plus triple-glazed windows (Ug ≤ 0.7). Add an air-to-water or air-to-air heat pump plus heat-recovery ventilation. Monthly heating cost in northern Poland (December): €65–110.
PIR 150 mm, double-layer walls, windows Ug ≤ 0.5, heat-recovery ventilation with 90%+ efficiency, photovoltaic panels. Investment cost is 30–50% higher, but annual bills are close to zero.
A well-insulated modular home is very airtight. This means that it must have ventilation — otherwise moisture settles on the walls and mould develops. The minimum is trickle vents in the windows plus a bathroom fan. The optimum: heat-recovery ventilation (€1,100–1,800, pays back in 3–4 years).
The year-round version is not just thicker insulation — it is a system. PIR thickness, window quality, wall airtightness, ventilation, and heating must all match one another. When placing your order, ask the manufacturer about a comprehensive winter package, not just about "an insulation upgrade".
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