A new nearly zero-energy (nZEB) house in Bulgaria: what the law requires, energy class, insulation, heat pumps and how to check your builder

If you are building a new house or buying one just completed, you have probably met the term nZEB — a "nearly zero-energy building". It is not a marketing label but a legal requirement. Yet there is a gap between the requirement on paper and how the house actually performs in winter, and that gap is down to workmanship. Here is what you need to know.

What the law says

Bulgaria's Energy Efficiency Act (ZEE) defines a nearly zero-energy building as one that meets both of two conditions (§ 1(28) of its Supplementary Provisions):

1. Its primary energy consumption falls within class A on the scale for that building type.
2. At least 55% of the energy delivered for heating, cooling, ventilation, hot water and lighting comes from renewable sources on site or nearby.

Ordinance No. RD-02-20-3 of 9 November 2022 on the technical requirements for the energy performance of buildings provides that, from 1 January 2024, all new buildings in the relevant categories are designed as nearly zero-energy buildings (Art. 21(1)(1)).

The EU is going further: under Directive (EU) 2024/1275 new buildings must become zero-emission buildings — public ones from 1 January 2028 and all others from 1 January 2030. A house built better than the minimum today will date more slowly.

Class A alone is not enough

A common mistake is to assume "class A" equals nZEB. Class A is only the first condition. Without a sufficient share of renewable energy — a heat pump and solar panels, solar thermal collectors or biomass, for example — a house can be class A and still fall short of the definition. Ask your designer exactly how the 55% threshold is met.

What makes a house genuinely low-energy

1. The envelope

• Continuous insulation of walls, roof and floor (or foundations) — no gaps at slabs, columns and corners.
• Minimal thermal bridges: at balcony slabs, thresholds and around windows.
• Good windows with triple or high-quality double glazing and proper three-layer fitting.

2. Airtightness
The house must be airtight — cold air should not leak in through joints, sockets and pipe penetrations. Airtightness is measured with a blower-door test. Builders experienced in low-energy houses usually do one — ask.

3. Heat-recovery ventilation
An airtight house needs controlled ventilation. A heat-recovery system returns much of the heat from outgoing air and protects against damp and mould.

4. Heating and renewable energy

• An air-to-water heat pump with underfloor heating is the most common solution.
• Rooftop solar covers part of the consumption. For existing single-family houses, installations up to 20 kW for own use need no building permit — only a notice to the municipal chief architect at least 14 days before installation (Spatial Development Act, Art. 151(1)(19) and (11)). For a new house it is simpler to include them in the design. More in our article on rooftop solar.
• Solar thermal collectors for hot water — a cheap, effective addition.

5. Orientation and shading
Large south-facing windows with an overhang or external blinds, smaller ones to the north. Good shading matters as much for summer as insulation does for winter.

The documents you should see

• The energy part of the design and the compliance assessment against energy efficiency requirements, as part of the investment design.
• An energy performance certificate — for new buildings, a certificate of designed energy performance. Audit and certification rules are set out in Ordinance No. E-RD-04-1 of 22 January 2016. A certificate for a building in use is valid for up to 10 years (ZEE, Art. 47(1)).
• Declarations and test reports for materials and tests — including the airtightness test, if one was done.

We covered the full route from building permit to entry into use in our guide to building your own house.

How to check your builder

• Ask for completed projects of a similar class and, if possible, real bills from the owners.
• Ask about details: how do they handle thermal bridges at the balcony, the foundations, the windows?
• Airtightness test — is it in the contract, and what result counts as acceptance?
• Technical supervision: independent supervision on your side is the best insurance.
• In the contract: a specific energy class and renewable share, not just "an energy-efficient house".
• Warranty periods and how defects are claimed — see our article on defects in new builds.

Is it worth it?

A better energy class usually means a higher upfront cost and much lower bills for decades. Energy class is also appearing in listings more often — see our article on energy class in listings. If you are financing the build or purchase with a loan, work out the repayment with our mortgage calculator and ask the bank about terms for energy-efficient buildings.

In short

• From 1 January 2024, new buildings are designed as nZEB.
• nZEB = class A + at least 55% renewable energy on site or nearby.
• The key is execution: continuous insulation, no thermal bridges, airtightness, heat recovery.
• A heat pump plus solar panels is the most common way to reach the renewable share.
• Put specific performance targets in the contract and hire independent supervision.

If you are building or looking for a new house and want to understand what you are really getting, call us or visit our office — we will go through the documents together.

This is general information and does not replace advice from a designer or energy efficiency consultant. Verified as of October 2026.