Chapter 3. Roof, Windows and Site Utilities. Blind area around a house: why you need it and how to do it right in 2026.

The blind area (otmostka) is the structure many people postpone — and then pay for foundation repair. Properly built, it protects the foundation from surface and meltwater, prevents frost heave and extends the building's life. Especially important in the Leningrad Region with its damp climate and deep ground frost (1.0–1.2 m).

Why it's mandatory

• Without it, water saturates the foundation, freezes and cracks the concrete in 5–10 years

• Frost heave creates lateral pressure on walls

• Damp basements grow mould

• Per SP 82.13330.2016, blind area is required for all buildings

Types

• Concrete (classic) — M200–M300, 80–100 mm thick. Cheap and durable but cracks over time.

• Paving slabs — on sand-gravel base. Aesthetic, repairable, 30–50% more expensive.

• Soft (hidden) — profiled membrane covered with gravel and topsoil/lawn. Doesn't crack, no maintenance.

Insulated blind area: critical here

Standard blind area diverts water but doesn't solve frost. Add XPS 50–100 mm (Penoplex Foundation, Technonicol Carbon Eco) — reduces frost depth at the foundation by 50–80%. Use 50 mm with shallow strip / Swedish slab, 100 mm on heaving soils or with basements.

Dimensions

• Width — at least 1.0 m (20 cm wider than the roof overhang)

• Slope from wall — 3–5° (30–50 mm/m)

• Concrete thickness — 80–100 mm

• Gap to wall — 10–20 mm with sealant or damper tape

Layered structure (bottom up)

1. Soil — excavate 300–400 mm, compact

2. Geotextile

3. Sand 100 mm with watering and tamping

4. XPS 50–100 mm with sealed joints, climbing 300 mm onto the plinth

5. Waterproof membrane

6. Gravel 20–40 mm fraction, 50–100 mm

7. M200–M300 concrete 80–100 mm with 100×100×4 mm mesh

8. Finish — ironed concrete, slabs or lawn

Expansion joints

Every 2–3 m, at corners, and between blind area and wall. Without joints concrete cracks in the first year.

Typical mistakes

• No insulation — frost heave continues

• Slope toward the house

• No expansion joints

• Too narrow (40–50 cm)

• Rigid attachment to the wall

• No reinforcement mesh

Cost per metre (1 m wide)

For a 40 m perimeter house an insulated concrete blind area costs 120 000–140 000 ₽. StroyInvest24 builds insulated blind areas of all types with technology compliance and warranty.

See also

• Foundation waterproofing

• Plot drainage in the Leningrad Region

• Foundation choice for the Leningrad Region

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