• nZEB (Nearly Zero Energy Building) has been mandatory in Romania since 2021, formalized through MC001/2022.
• An nZEB building consumes between 120 and 148 kWh/m²/year, depending on the climate zone.
• At least 30% of the required energy must be produced from renewable sources.
• Thermal insulation, airtightness, and heat-recovery ventilation are core components, not optional.
• A house correctly built to nZEB principles can reach annual heating bills of RON 400–600.
  
  

nZEB. A term used more and more in construction. It appears in designs, on building sites, in discussions with the architect or the construction company. But it is not just a word. Since 2023, nZEB has been the law. The MC001/2022 methodology was published in the Official Gazette and, since then, every new building in Romania must meet these requirements.

Many people hear nZEB and get worried. It sounds complicated, it sounds expensive, it sounds like bureaucracy. But in fact, nZEB is not here to make life harder. It is here to ensure that a new home will not waste energy, will be comfortable, and will not depend on resources that get more expensive year after year.

In this article, we look at what nZEB means in practical terms, what such a building is made of, and how it helps in the long run.

What nZEB means, in practical terms

nZEB comes from Nearly Zero Energy Building. In Romanian: a building with energy consumption close to zero. In Romania, the official spelling uses a capital N, according to the MC001/2022 methodology published in the Official Gazette on January 17, 2023.

What does the official definition say? That an nZEB building has very high energy performance, and that the energy consumption for operation is very low. And this energy, however small, must be covered at a minimum of 30% from renewable sources.

The regulation comes from EU Directive 31 of 2010 on the energy performance of buildings. Each member state transposed it into its own legislation. Romania formalized it late, but since its publication in the Official Gazette, it is the law.

In practical terms, an nZEB building in Romania must meet three main requirements:

1. Total primary energy consumption below the limit.
Romania has 4 climate zones, and the total allowed consumption for a single-family house is between 120 and 148 kWh per square meter per year. This includes heating, cooling, ventilation, domestic hot water, and basic lighting.

2. Greenhouse gas emissions below a maximum value.
Each climate zone has a specific limit, set out in the methodology.

3. At least 30% of energy from renewable sources.
The simplest way to get there is with photovoltaic panels. Renewable sources located within a 30 km radius of the building are also accepted.

What an nZEB building is “made” of

An nZEB building is not a house with complicated systems and technical rooms the size of a garage. First and foremost, it is a well-built house. The systems come as a consequence of how the building is designed and executed, not the other way around.

Generous thermal insulation

The principle is simple. When we go skiing, we dress warmly to retain body heat. The same applies to a house. The better insulated the thermal envelope is, the less energy we lose.

The methodology recommends at least 15 cm of insulation on the façade, 25 cm on the roof, and 12–15 cm at the foundation. The values are given through thermal transmittance coefficients (U-value), where for exterior walls a maximum of 0.25 W/m²·K is recommended, and for the roof a maximum of 0.15 W/m²·K.

No thermal bridges

No matter how good the insulation is, if there are interruptions, heat is lost exactly there. A balcony slab that penetrates the insulation works just like a ski jacket that is two centimeters shorter than the pants. An exposed belly cancels all the effort.

The same happens with foundations poured directly into the ground, without insulation. The argument that “the ground keeps it warm” does not match reality. It is warmer than air, but the losses are constant. When skiing, nobody sets off in flip-flops. For a house, an uninsulated foundation is the exact equivalent.

Airtightness

Warm air in the house contains energy. To reach 20°C, you have consumed gas, electricity, or pellets. If this air escapes uncontrollably through cracks, gaps, or weak joints, that energy is lost. It is like a jacket with a broken zipper. You can have the best fabric, but if it does not close, it does not help.

For nZEB, the recommendation is an airtightness level below 1.5 air changes per hour at 50 Pa. An airtightness test (blower door test) is also recommended, especially for buildings where real performance is the goal.

High-performance windows

Windows are, most of the time, the most expensive element in a house. The price ranges between €200 and €1,000 per square meter. That is why how they are selected and positioned matters enormously.

In nZEB, the thermal transmittance coefficient for windows must be at most 1.11 W/m²·K. But beyond the U-value, it also matters how the window interacts with the sun. A well-oriented window can gain more solar energy than it loses. This calculation is called the energy balance and is done for each window, on each façade.

Heat-recovery ventilation

In winter, windows stay closed. The air in the house still needs to be refreshed. A heat-recovery ventilation system solves exactly this problem. It works on a simple principle: the warm air leaving the house passes through a heat exchanger, where it transfers its temperature to the cold air coming in. The two air streams do not mix; they only transfer energy.

Current systems recover over 90% of the heat. If it is 20°C inside and minus 10°C outside, fresh air enters the house at about 17°C, not minus 10°C. The difference in energy effort is enormous.

The nZEB methodology recommends systems with efficiency above 70%. It is not listed as mandatory, but in practice, without such a system it is very difficult to meet the imposed energy consumption limit.

Renewable energy sources

At least 30% of the building’s primary energy must be produced from renewable sources. The most accessible way is through photovoltaic panels. Nearby sources within a 30 km radius are also accepted.

If a building runs exclusively on electricity (no gas), reaching the 30% target is simpler. If a gas boiler is also used, the number of panels required increases considerably, because a higher total consumption must be offset.

The real benefits of an nZEB home

Significantly lower bills

The difference is not theoretical. A 2,400 m² office building built to high energy-efficiency principles in Oradea recorded a cost of RON 3.6 per square meter per year for heating and cooling. Houses of around 150 m² built to high standards have annual heating bills between RON 400 and 600.

These figures do not include “tricks” or exotic equipment. They include proper insulation, good windows, airtightness, and heat-recovery ventilation.

Real energy independence

The less a house consumes, the less it depends on energy price fluctuations. An nZEB home with correctly sized photovoltaic panels can cover a significant part of its consumption on its own. And in a context where gas and electricity prices show no signs of falling, this independence becomes a tangible advantage.

Superior thermal comfort

A well-insulated and airtight house has no cold spots near windows, no drafts, and maintains a uniform temperature. This is not about luxury. It is about physics. The nZEB methodology also includes comfort-related requirements: interior surface temperatures, relative humidity, air velocity. There is even a mandatory factor (fRsi) that checks whether condensation or mold can occur on interior surfaces. Because mold does not pay rent, but it costs money to fix.

Long-term value

nZEB requirements will increase. From 2030, the share of renewable energy rises to 45%. From 2040, to over 60%. From 2050, to over 80%. Those who build now to the minimum nZEB level will have to make additional investments with each update. Those who build better from the start will have a compliant home even in 20 years, without interventions to the envelope.

Insulation lasts 50 years. Equipment is replaced after 20–25 years. The harder equipment has to work to compensate for a weak envelope, the faster it wears out. The logic is simple: invest in the shell of the house, and the equipment will be smaller, cheaper, and last longer.

nZEB is not an obstacle; it is an investment

The most common fear about nZEB is cost. “It costs too much.” “It is complicated.” “It is not worth it.”

Let us put things in context. Globally, the construction sector is responsible for about 40% of polluting emissions. And of that 40%, around 70% comes from the use of buildings, not from manufacturing materials. Heating in winter, cooling in summer, hot water, lighting. All consume energy. And most of that energy still comes from fossil sources.

In Romania, natural gas has become steadily more expensive over the past 30 years. There has been no period in which the price fell and stayed there. Since 2022, with the war in Ukraine, Europe’s dependence on Russian gas has become a security issue, not just a comfort issue. Nobody knows what gas will cost in 10 years. But it is clear it will not cost less than it does today.

In fact, nZEB emerged precisely as a response to this reality. A house that does not depend on gas for heating is a house that will not be affected by the next energy crisis.

And the methodology states clearly: the additional investment in an nZEB building must lead to a minimum global cost within a maximum of 30 years. The difference in construction cost is recovered through energy savings. This is not thinking for tomorrow, but a calculation over the home’s real operating life.

Investing in nZEB is not a cost. It is insurance.

Where the Passive House stands in relation to nZEB

nZEB is mandatory. The Passive House standard is optional, but internationally recognized in over 120 countries.

The requirements are stricter: insulation with U below 0.15 W/m²·K for walls (vs. 0.25 for nZEB), windows with U below 0.85 (vs. 1.11), airtightness at 0.6 air changes per hour (vs. 1.5), and mandatory heat-recovery ventilation with at least 75% efficiency.

In practice, a passive house consumes 2–3 times less energy than an nZEB building. It does not necessarily need photovoltaic panels, because the energy demand is already so low that renewable production becomes a bonus, not a necessity.

What is relevant: the two standards are converging. In 2050, nZEB requirements will be practically identical to those of today’s Passive House. Those who choose to build now to the Passive House standard are, in fact, anticipating the requirements of more than 25 years from now.