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Over the years of working in construction, we have seen dozens of projects where clients made the same mistakes over and over again. Some errors cost tens of thousands of rubles, others — millions. Let’s go through the most common ones so you don’t repeat them.
“Why do we need a project? We already know what kind of house we want” — this is the phrase that usually leads to problems. Without a project, it is impossible to:
Accurately calculate the amount of materials (15–30% overspending)
Properly design the foundation according to loads
Coordinate the placement of load-bearing walls and floors
Plan engineering systems without conflicts
A project costs 80,000–250,000 ₽. Mistakes without a project cost 10 times more.
The foundation is 8–12% of the house cost, but 100% of its reliability. Common mistakes:
Skipping geological surveys. Building a strip foundation on peat soil — the house “floats” within a year. Geology costs 20,000 ₽; fixing the foundation costs from 500,000 ₽.
Insufficient depth. A foundation above the frost depth (1.2–1.5 m for the Leningrad region) will be lifted by frost heave.
Weak reinforcement. Rebar Ø8 instead of Ø12, no ties, overlap less than 40 diameters — all this leads to cracks.
For the Leningrad region, insulation is not optional — it is essential. Typical mistakes:
Thermal bridges. Gaps between insulation boards, untreated joints of walls and floors, uninsulated window slopes. Each thermal bridge leads to condensation, mold, and heat loss.
Incorrect vapor barrier. In a frame house, vapor barrier must be inside, wind protection — outside. Confusion leads to wet insulation. Wet mineral wool loses up to 80% of its insulating properties.
Insufficient thickness. 100 mm of insulation in a frame wall is not enough for this region. Minimum — 150 mm, optimal — 200 mm.
“The roof is just boards and metal” — a misconception that leads to leaks, ice buildup, and expensive repairs.
Insufficient ventilation of the under-roof space. Without vents in the eaves and ridge, moisture condenses on the sheathing and rafters. After 3–5 years — rot.
No counter-batten. Without a ventilation gap between waterproofing and roofing material, condensation does not escape.
Saving on snow guards. In the Leningrad region, snow load is 180 kg/m². Sliding snow can damage gutters, porches, or even injure people.
The cheapest offer is almost always the most expensive in the end. Signs of an unreliable contractor:
No legal entity (working as individuals)
No real project portfolio
No detailed estimate — only an “approximate price”
Requesting 50–70% upfront payment
No proper contract or a vague one
No warranty
Signs of a reliable contractor: legal entity, portfolio with real addresses, detailed estimate, staged payments, fixed-price contract, warranty from 3 years.
Utilities must be planned at the design stage, not after the walls are built. Common issues:
Sewer pipe passing through the foundation — sleeves must be installed before pouring concrete
Insufficient electrical input capacity — 15 kW load requires a 10 mm² copper cable or 16 mm² aluminum
No ventilation — in energy-efficient homes without supply ventilation, humidity can reach 80%, leading to mold
Even with the best contractor, you should monitor the process:
Request photo reports at every stage
Visit key acceptance stages (foundation, walls, roof)
Check materials against specifications
Hire technical supervision (50,000–100,000 ₽) — an investment that pays off
Experienced construction companies organize reporting and inspections themselves — for them, it’s standard practice. If a contractor avoids oversight, it’s a red flag.
Most of these mistakes have one thing in common — the lack of a systematic approach. When construction is done “on the go,” without a project, without control, and without a single responsible party, problems are inevitable.
At StroyInvest24, every project starts with design and geological surveys, is carried out based on a detailed estimate, and is supported by photo reports at every stage. Our own crews, staged payments, and a 5-year warranty are not marketing claims — they are contract terms.
Over the years of working in Saint Petersburg and the Leningrad region, we have built a large number of homes and know how to avoid every one of these mistakes.
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