Chapter 2. Utilities and Heating. Insulating a timber frame house: materials, wall assembly and installation.

A timber frame house is essentially a thermos. Its thermal performance is defined almost entirely by the insulation and how correctly the wall assembly is built. In the Leningrad Region (−26 °C design temperature, 220+ day heating season) insulation mistakes are expensive — wasted fuel, cold bridges, condensation and mould.

Insulation materials

Mineral (basalt) wool

The most popular for frame walls. Brands: Rockwool, Paroc, Tekhnonikol. Thermal conductivity 0.035–0.042 W/(m·K), non-combustible, vapour-open, density 30–50 kg/m³ for walls. Loses performance when wet — needs internal vapour barrier and external windproof membrane.

Cellulose (ecowool)

Blown-in cellulose with borate fire retardants. 0.037–0.042 W/(m·K), seamless fill, good acoustics. Settles 10–15% over time (dry blow); needs specialist equipment.

PIR / PUR boards

Premium. 0.022–0.025 W/(m·K) — nearly twice as effective as mineral wool. 80 mm PIR = 150 mm wool. Non-absorbent. 3–4× more expensive; often used as an extra outer layer over the studs to break thermal bridging.

Expanded polystyrene (EPS)

Not recommended for frame walls. Vapour-tight — traps moisture; in 2–3 years the frame rots. OK for floors, plinth and foundation only.

Wall assembly (inside out)

1. Internal lining — GKL 12.5 mm or tongue-and-groove on battens (service cavity)

2. Vapour barrier — film (Izospan B, Delta Reflex) on the warm side, taped, overlap ≥150 mm

3. Insulation — basalt wool 200 mm in 2 × 100 mm layers with staggered joints

4. External sheathing — OSB-3 9–12 mm or cement-bonded board

5. Wind/moisture membrane — vapour-open (Izospan A, Tyvek, Delta Vent N), NOT another vapour barrier

6. Ventilation gap — 20–40 mm battens, carries moisture upward

7. Cladding — siding, plank, planken

Thermal resistance for Leningrad Region

Required R = 3.08 m²·K/W (SP 50.13330.2012, HDD ~4800).

5.4 significantly exceeds the 3.08 requirement — real efficiency, not bare compliance. With 150 mm wool R≈4.0 — also passes but with less margin.

Common mistakes

• Vapour barrier on the outside instead of windproof membrane — frame rots in 2–3 years

• Gaps between insulation slabs — 5 mm is already a cold bridge

• No ventilation gap — membrane useless

• Wrong membrane orientation — reverse effect

• Untaped vapour barrier joints — as bad as having none

Cost per m² of wall (2026)

For a 100 m² house (120–150 m² of wall) — 320 000–650 000 ₽. PIR instead of wool raises the budget 40–60% but reduces wall thickness.

StroyInvest24 insulates frame houses across the Leningrad Region with strict technology control at every stage — from vapour barrier to final cladding.

See also

• Floor insulation

• Roof and mansard insulation

• Underfloor heating in a frame house

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