An almost-zero-energy home is designed by reducing energy demand before choosing photovoltaic panels. Building form, orientation, insulation continuity, windows, shading, airtightness and systems must be planned as one system. Only once demand is low does it make sense to calculate the contribution from renewable energy.
For a new home in Romania, nZEB is not merely a commercial label. Law No. 372/2005 on the energy performance of buildings provides that new buildings accepted on the basis of permits issued from 31 December 2020 onwards must fall within this category. The urban planning certificate requires an nZEB compliance report, prepared at the design stage, which verifies the level of total primary energy consumption calculated under the national methodology.
For more information on passive houses, see also XPS beneath a home’s slab: 5 cm, 10 cm or 15 cm? Grounding, waterproofing and 15 essentials for an efficient home, which provides complementary details on this subject.
The key point for the client is simple: an nZEB home cannot easily be “fixed” at the end by adding equipment. If the design has large façade areas, many setbacks, windows exposed to summer sun, or thermal bridges at the foundation and roof, the systems will become larger, more expensive and harder to control.
nZEB does not mean zero bills or an off-grid home
In technical documentation, nZEB means a building with very high energy performance, very low energy demand and a relevant share of energy covered from renewable sources. Under the current version of Law No. 372/2005, the share of energy from renewable sources is 30% of total primary energy consumed, calculated using the energy-performance methodology.
This wording explains why the promise that “you will have zero energy bills” should be treated cautiously. The compliance calculation uses a standardised usage scenario and primary-energy indicators. The actual bill also depends on factors that vary from one household to another: preferred room temperatures, number of occupants, hot-water use, appliances, working from home, actual shading of the panels and how the systems are operated.
A home connected to the electricity grid can be nZEB. Likewise, an nZEB home can import energy in winter or in the evening and export energy in summer if it has photovoltaic panels. Independence from the grid requires a separate assessment of periods with very low production, the power needed simultaneously and storage capacity. For this scenario, it is also worth reading the article on designing an off-grid home based on the toughest week of winter.
| Commonly used label | What it actually means | What it does not guarantee on its own |
|---|---|---|
| nZEB home | Meets national requirements for energy performance, primary energy and renewable-energy contribution. | Zero energy bills, autonomy or Passive House certification. |
| Passive house | A much more demanding voluntary standard, with its own criteria for heating demand, airtightness and renewable primary energy. | Automatic compliance with all local formalities without project verification in Romania. |
| Autonomous home | Can operate without a permanent connection to certain networks if generation and storage also cover unfavourable periods. | Low consumption; autonomy achieved through oversized equipment can be expensive. |
| Zero-emission building | The European standard that will become the benchmark for new buildings, under the conditions set by national transposition legislation. | That every new home is already automatically classified in this category. |
Design starts with geometry, not an equipment list
The first energy decision is the building’s form. A compact home generally has less surface area through which it loses or gains heat in relation to its internal volume. This does not mean that every home must be a cube, but that every setback, terrace included in the volume, bay window or cantilever must be justified and technically resolved.
The architect and energy auditor must work from the same house model before solutions are finalised. At this stage, they test room orientation, the proportion of glazing, shading, wall types, floor slabs, roof and foundation. A large south-facing window may help in winter, but without external solar protection it can turn the room into a space that is difficult to cool in summer.
In Romania, the Mc 001-2022 methodology sets out the energy-performance calculation and allows differentiated requirements by building use. Local climatic conditions, site location and geometry are not decorative details: they change the calculation result. This is why a package of solutions copied from a home built in another city or with a different orientation is no guarantee of compliance.
The thermal envelope must be drawn as continuous
Insulation is not simply a number of centimetres stated in a cost estimate. What matters is whether the thermal-insulation layer is continuous at the plinth, around windows, at the balcony, where the wall meets the roof and in areas where structural elements penetrate it. A local interruption is a thermal bridge: a path through which heat partly bypasses the insulation.
Thermal bridges have three effects: they increase heating demand, locally cool the interior surface and may increase the risk of condensation and mould if indoor humidity is not controlled. The relationship between the envelope, condensation and ventilation is explained in greater detail in the article on mould appearing after replacement windows or renovation.
At the foundation, ground slab and plinth, the decision must be coordinated with the waterproofing detail, the structure and service routes. Adding an insulation solution later “where it fits” can compromise the continuity on which the initial energy calculation relies.
Windows are chosen by the whole assembly and installation
A window quotation must be read carefully. The relevant value for the complete window is Uw, not just the glazing performance. The profile, spacer, size and frame proportion matter, as do the position of the window in the wall and sealing of the installation joint.
In an efficient home, a window is simultaneously a source of light, an element of the envelope and a potential overheating zone. Fixed or movable external shading must be provided for in the architectural design, rather than treated as an optional accessory after moving in. For criteria to compare windows, including the difference between Uw, glazing and installation, see the article on choosing windows for an efficient home.
Systems enter the design after loads have been reduced
Once the architecture and envelope have been established, the building-services designer can size the heating source, distribution system, hot water, ventilation and cooling. The order matters. A system calculated for a house with high losses can become unnecessarily large if the design is subsequently improved; conversely, a heat pump selected from a catalogue before the calculations may operate less efficiently or cycle on and off too often.
A heat pump is not in itself a mandatory requirement for an nZEB home, but it often suits a design with low demand and low supply temperatures, for example through properly sized underfloor heating. Its selection should be based on calculated losses and the hot-water production method, not on the home’s area estimated “by eye”.
Ventilation should be treated as part of comfort and building protection, not merely as equipment that affects the energy balance. In an airtight home, airing by opening windows can be useful, but it does not provide a constant, controlled airflow. A heat-recovery system can limit the energy loss associated with fresh air, but it requires routes designed early, maintenance access and proper commissioning. Practical details are available in the analysis of heat-recovery ventilation in a new home.
What is checked before the permit and what can be lost on site
The nZEB compliance report should be requested early, ideally before the architectural design is finalised. According to Law No. 372/2005, the report is prepared by a grade I building energy auditor and certifies that total primary energy consumption falls within the levels set by the calculation methodology. It also includes a feasibility analysis of high-efficiency alternative systems.
The report should not be viewed as a formality to be placed in the file. It is the point at which the design can still be adjusted inexpensively: the position of a window can be changed, shading corrected, a component’s performance increased, or a different combination of heat source and renewable energy chosen. Once the foundation has been poured, changes become far more limited.
At acceptance, the energy performance certificate must reflect the building as constructed. This is where one of the greatest risks arises: substitutions of materials and equipment. Windows with different characteristics, less insulation, a ventilation system removed from the budget or postponed photovoltaic panels can change the result compared with the assessed design.
Four checkpoints for the client
- Before permitting: ask the architect, building-services designer and energy auditor to work from the same version of the plans. Check the nZEB report, not merely the mention of “nZEB” in the quotation.
- At the technical-design stage: request drawn details for the plinth, window perimeter, wall-to-roof junction, penetrations and sealing. These areas often determine the difference between a rendering and the built home.
- During construction: keep the technical data sheets for installed products and compare them with those specified in the design. Do not accept equivalents without confirmation from the designer and, where performance is affected, the energy auditor.
- Before acceptance: check that the specified systems are present, operational and have been adjusted. Request clear instructions for use, maintenance and the basic settings for ventilation and heating.
nZEB, passive house and the coming European standard
An nZEB home can be very good, but it is not automatically a certified passive house. The voluntary Passive House Institute standard is stricter and uses its own criteria. Its benchmarks include an annual heating demand of no more than 15 kWh/m²/year or a heating load of no more than 10 W/m², as well as n50 airtightness of no more than 0.6 air changes per hour in a pressure test.
At European level, Directive (EU) 2024/1275 raises the standard for new buildings to that of zero-emission buildings from 2030; for new buildings owned by public bodies, the deadline is 1 January 2028. The European definition emphasises very high performance, no on-site carbon emissions from fossil fuels, and zero or very low operational emissions. The specific implementation requirements must be set out in national legislation.
The direction is relevant even for a project started now: a home with a robust envelope, systems that can be electrified and a technical space designed for maintenance is easier to adapt than one dependent on a rigid solution. However, there is no need to buy every available technology from the outset. The most valuable “equipment” remains a well-designed, well-executed envelope, because it cannot be easily replaced after moving in.
The right question for the design team
Instead of asking, “How many panels do I need for it to be nZEB?”, the useful question is: “What are the home’s calculated losses and gains, which solutions were compared, and which construction elements cannot be changed without recalculating?”
A good answer must connect architecture with systems and compliance documents. If the project starts this way, the panels, heat pump and possible battery are no longer isolated products, but the final pieces of a home that needs little energy before trying to generate it.
Frequently asked questions
Is a heat pump mandatory for an nZEB home?
No. nZEB compliance is assessed through calculated overall energy performance, the contribution from renewable sources and the requirements of the applicable methodology. A heat pump is a common solution, not an automatic requirement.
Are photovoltaic panels mandatory for an nZEB home?
Not automatically. Renewable energy can come from different solutions, depending on the project and the technical-economic analysis. However, photovoltaics are among the most common options for covering part of the calculated demand.
Does an nZEB home have zero electricity use?
No. nZEB is a calculated energy-performance standard, not a promise that there will be no bills. Actual consumption depends on occupancy, set temperatures, hot water, appliances, weather and system operation.
When should the nZEB compliance report be prepared?
At the design stage, before obtaining the building permit. The report is requested through the urban planning certificate to demonstrate that the project meets the applicable requirements.
Is a blower-door airtightness test mandatory for nZEB?
The blower-door test is a highly useful check of construction quality, especially for ambitious projects, but it should not be confused with the specific requirements of Passive House certification. The client should confirm with the auditor and designers which checks are specified in the contract and project documentation.
