Why prefabricated houses are so energy-efficient
A client once sent us a photo of her January electricity bill for a 120 m² Treevia house, with a one-line message: "is this right?" It was right - somewhere in the PLN 150-250 a month range, against the PLN 500-1,000 a traditional house often costs to heat in the same season. That gap isn't magic. It comes from precise manufacturing, considered construction and modern installations working together.
Airtightness comes first
The real enemy of a building's energy performance isn't thin insulation - it's uncontrolled air leaks. Every gap, every imprecise joint, every seam air can sneak through is heat loss that no amount of insulation will make up for.
In prefabrication, wall panels leave the hall as complete assemblies - structural layer, insulation, vapour barrier, wind protection, all built in together. The joints between panels are designed and executed to millimetre tolerances.
Every Treevia house is Blower Door tested, and our results come in at n50 < 1.5 1/h - well ahead of the n50 < 3.0 1/h benchmark typically used for energy-efficient buildings.
A wall with many layers, each doing a job
A Treevia wall isn't just "timber plus insulation." From inside to outside, it's a deliberate stack:
- Plasterboard - the interior finish
- Installation space - room for electrics and plumbing without piercing the vapour barrier
- Vapour barrier membrane - stops moisture migrating from the interior into the structure
- Timber structure with insulation - mineral wool or cellulose, 15-20 cm thick
- Wood-based board (e.g. OSB) - the stiffening layer
- Wind protection - shields the insulation from wind and outside moisture
- Ventilated facade - timber, render or facade panel over a ventilated air gap
The result: a wall U-value of U ≤ 0.15 W/(m²K), clearly ahead of the current regulatory maximum of 0.20 W/(m²K) for external walls.
Heat from the air
Treevia houses use underfloor heating as the distribution system, and the client chooses the heat source. Modern heat pumps run at a COP of 3.5-5.0 - meaning every 1 kWh of electricity in returns 3.5-5 kWh of heat.
Paired with a tight, well-insulated envelope and underfloor heating, that translates into heating costs of roughly:
- 70 m² house - PLN 80-150/month, annual average
- 120 m² house - PLN 150-250/month
- 220 m² house - PLN 200-350/month
These are illustrative figures for a specific heat source, not a guarantee - climate, household habits and the exact system all move the number.
Ventilation that recovers heat instead of wasting it
A recuperator pulls 85-95% of the heat out of stale exhaust air and puts it back into fresh incoming air. You get clean, filtered air without opening a window and without throwing heat away in the process.
It also brings:
- Filtration - HEPA filters catch pollen, dust and smog, which matters if anyone in the house has allergies
- Stable humidity - no more steamed-up windows
- Quiet - no need to crack a window in a noisy area
Putting numbers side by side
For a 120 m² house in central Poland:
Traditional brick house, gas and radiators:
- Annual gas use: roughly 1,500-2,000 m³
- Annual cost: PLN 6,000-10,000
Treevia house with heat pump, underfloor heating and recuperation:
- Annual electricity for heating: roughly 3,000-4,500 kWh
- Annual cost: PLN 2,000-3,000
The gap: PLN 3,500-7,000 a year. Stretched over 30 years, that's PLN 100,000-210,000.
The point of all this
At Treevia, energy efficiency isn't an upsell - it's the baseline every house is built to. Airtight construction, multi-layer walls, recuperation and underfloor heating work as one system, where comfortable living and a low monthly bill aren't a trade-off.
Curious what that would look like for your own house? Get in touch and we'll walk through the numbers for your plot and plans.