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An uninsulated floor loses 20–30% of the house's heat. In the Leningrad Region (ground freezes to 1.2–1.5 m, January often −25…−28 °C) floor insulation is mandatory. Three main floor types, each with its own optimal scheme.
Classic for frame houses on helical piles or posts. Insulation between joists.
Under-joist sheathing — 25 mm board or OSB
Wind/moisture membrane (critical for open under-floor on piles)
Insulation — mineral wool 30–50 kg/m³, 200–300 mm in 2–3 staggered layers
Vapour barrier (Izospan B) above insulation, taped, ≥150 mm overlap
Subfloor — 18–21 mm plywood or 2×12 mm OSB-3
Finish — laminate, engineered board, linoleum
Key rule: vapour barrier on the warm side, windproof membrane on the cold side. Reversed = condensation and rotten joists.
Compacted soil
Sand bed 100–200 mm, compacted in 50 mm lifts
Crushed stone 100 mm, 20–40 mm fraction
Optional 50–80 mm blinding concrete
Waterproofing — 2× 200 µm PE film or bitumen membrane
XPS 100–200 mm in two staggered layers, L-edge
Separation film
Reinforced screed 70–100 mm, 100×100 mm mesh, d4
Perimeter expansion tape
Finish — tile, porcelain, laminate
Similar to on-ground but no soil prep. Waterproofing simplified (paint-on). XPS 50–100 mm above heated space, 100–150 mm above cold basement.
Material | λ W/(m·K) | Use | Absorbs water | ₽/m² (100 mm) |
|---|---|---|---|---|
XPS (Penoplex) | 0.029–0.034 | On ground, plinth | No (<0.5%) | 500–800 |
Mineral wool | 0.035–0.042 | On joists | Yes (needs vapour barrier) | 350–600 |
PIR (Logicpir) | 0.022–0.025 | Any | No | 900–1 400 |
Expanded clay (10–20 mm) | 0.10–0.18 | Budget on-ground | Partially | 150–250 |
XPS — best for on-ground and slab. 50+ years service life. Density ≥35 kg/m³ under screed — 25 kg/m³ boards crush.
Wool — optimal on joists; not for on-ground (absorbs moisture without ventilation).
PIR — minimum thickness at maximum efficiency. 60 mm PIR = 100 mm XPS.
Required R = 3.6–4.2 m²·K/W.
Structure | Insulation | Min, mm | Recommended, mm |
|---|---|---|---|
On ground | XPS | 100 | 150–200 |
On ground | PIR | 80 | 100 |
On joists | Mineral wool | 200 | 250–300 |
On joists | PIR | 100 | 150 |
On slab (cold basement below) | XPS | 100 | 150 |
No vapour barrier in joist floor — humid air condenses in wool, joists rot
Gaps between XPS boards — cold bridges. L-edge or stagger the second layer
Wrong XPS density — need ≥35 kg/m³ under screed
No expansion tape — screed cracks, tiles delaminate
Expanded clay without waterproofing — becomes a moisture sink
Insulation not tight to walls — perimeter cold bridge
Excavate to design level
Sand bed 150 mm, compacted in lifts
Crushed stone 100 mm
Optional blinding concrete 50 mm
Waterproofing with 200 mm overlaps, 150 mm up walls
XPS layer 1 (100 mm)
XPS layer 2 (50–100 mm), staggered joints
Separation film
Perimeter expansion tape
Mesh on 20 mm spacers
Underfloor heating pipes (if fitted)
Screed 70–100 mm to level beacons
Cure 28 days
Item | ₽/m² |
|---|---|
Sand-gravel prep | 250–400 |
Waterproofing (200 µm film) | 50–80 |
XPS 150 mm | 750–1 200 |
Expansion tape | 30–50 |
Mesh + spacers | 150–250 |
Screed 80 mm (material) | 350–500 |
Labour | 600–1 000 |
Total | 2 200–3 500 |
Item | ₽/m² |
|---|---|
Under-joist sheathing | 200–350 |
Windproof membrane | 60–100 |
Mineral wool 250 mm | 700–1 100 |
Vapour barrier + tape | 80–120 |
Top subfloor (plywood / OSB) | 350–550 |
Labour | 500–900 |
Total | 1 900–3 100 |
For a 100 m² house — 190 000–350 000 ₽ depending on construction and materials.
StroyInvest24 insulates all floor types in the Leningrad Region — correct material selection, strict installation technology and quality control at every stage.
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