When building or renovating a residential house, energy efficiency class is not just a formality. Stricter building regulations that came into force in Lithuania in 2021 require all new buildings to meet at least class A, and in some cases even A+ or A++. Therefore, every builder, designer, or renovator must clearly understand what the A class requirements are, how they differ from other classes, and what the main risks are if they are not met.
What does energy efficiency class A mean?
Class A is one of seven energy efficiency classes for buildings, determined by energy consumption for heating, hot water, ventilation, and overall building airtightness. The higher the class, the more energy-efficient the building is.
According to the Technical Regulations for Construction STR 2.01.09:2012, a Class A building:
- must be well insulated, maintaining strict thermal resistance parameters;
- be airtight, i.e., there should be no “leaky joints” between structures;
- be equipped with an efficient engineering system – economical heating, hot water supply, and ventilation.
For comparison: Class B buildings consume more heat, their enclosures often do not meet the required resistance, and Class C houses usually do not meet either airtightness or insulation requirements. Therefore, although Class B is still permissible in some situations (e.g., for renovation), Class A is the minimum requirement for new residential buildings.
“Class A is a turning point between old, energy-inefficient solutions and modern, efficient construction. It is no longer an aspiration – it is a mandatory standard,” says Kęstutis Butkus, a building energy efficiency assessor.
Important: Class A requirements are calculated not only based on insulation materials, but also on the geometry of the building, the heating system, orientation, window and door characteristics, and airtightness.
Class A construction and structural requirements
In order for a residential building to comply with energy efficiency class A, clearly regulated technical solutions must be implemented. These include both the thermal properties of structures and detailed requirements for windows, doors, and installation quality. Based on STR 2.05.01:2013 “Energy efficiency design of buildings”
Thermal resistance of external envelopes
The envelope of a Class A building must retain heat and prevent it from escaping through the structural layers. Therefore, the following minimum thermal resistance requirements apply to walls, roofs, and floors:
- External walls – not less than R = 5.0 (m²·K)/W
- Roof or ceiling – not less than R = 6.0 (m²·K)/W
- Floors on ground – not less than R = 4.0 (m²·K)/W
These parameters can only be achieved by using modern thermal insulation materials (e.g., rock wool, polyurethane, PIR boards), which must be installed consistently, without gaps or cold bridges.
Heat transfer requirements for windows and doors
Windows and doors are structural elements that usually let in the most heat. Therefore, their parameters are strictly regulated in Class A houses:
- Uw coefficient for windows – no higher than 0.9 W/(m²·K)
- Door U-value – no more than 1.3 W/(m²·K)
These indicators must be assessed not only during the design phase, but also during the actual installation of the structures. Windows must be installed tightly, using layered installation technology to avoid even the slightest leaks.
Construction errors that prevent achieving the class
The most common problems that prevent achieving Class A are not related to the design, but to the quality of construction. Improperly joined materials, gaps left at joints, or poorly insulated foundations all reduce the efficiency of a building. Another mistake is insufficient attention to roof or floor insulation, when the entire energy load is transferred to the walls.
“Most often, classes are not achieved due to installation errors rather than materials. No certificate will help if a window is installed with a gap and the insulation is interrupted at the beam,” says Jonas Račkauskas, construction technical supervisor.
Engineering systems and energy efficiency
Although the thermal properties of a building are an essential criterion for Class A, good insulation alone does not guarantee the required energy efficiency. The engineering systems installed in the building – heating, ventilation, hot water supply, and the use of renewable energy sources – also have a significant impact.
Heating system requirements
A Class A house must have an efficient and economical heating system. Although legislation does not prohibit the use of traditional boilers or electric heaters, they must be automatically controlled and meet minimum energy efficiency requirements.
Heating systems with heat pumps (air-water or ground-water) offer the greatest benefits, as their coefficient of performance (COP) often exceeds 3, which means that they produce 3 kWh of heat for every 1 kWh of electricity consumed. This efficiency directly contributes to lower energy demand, which is assessed when calculating the energy performance class of a building.
Ventilation with heat recovery
A mechanical ventilation system with heat recovery is currently an integral part of a Class A building. This system not only ensures high-quality air exchange in the premises, but also reduces heat loss, as the heat from the exhaust air is used to heat the supply air.
According to STR 2.05.01:2013, the design of ventilation systems must be based on the actual needs of the premises, and the heat recovery coefficient (η) of the recuperator should be at least 75%. In other words, the more heat is saved, the greater the likelihood of achieving Class A.
Hot water supply
Hot water systems are also included in the energy performance assessment. The most efficient solutions are solar collectors or combined heat pumps that heat water together with the heating system. The integration of such systems often reduces energy demand and improves the overall class rating.
Verification and documentation of Class A requirements
In order for a building to be classified as Class A energy efficiency, it is not enough to simply declare that warm materials or efficient systems are used. All of this must be substantiated by calculations and official documents that are evaluated by competent authorities.
Energy performance certification
After completion of construction work, the building must undergo energy performance certification. This process is based on special calculations performed by certified building energy performance assessors. The assessment takes into account:
- the heat transfer coefficients of all building envelopes;
- the efficiency of heating, ventilation, hot water supply, and electrical systems;
- the energy demand per square meter per year;
- the amount of renewable energy that can be used (if applicable).
If all data complies with the applicable requirements, an energy performance certificate is issued, indicating the building class from G to A++.
Who performs supervision?
During construction, technical supervision is carried out by a technical supervisor appointed by the builder, but the most important thing for the final assessment is the submission of the building to the State Territorial Planning and Construction Inspectorate. A building cannot be approved for use without an energy performance certificate.
It is important to know that the building inspection authority may reject the building declaration if the actual construction work or materials used do not meet the parameters specified in the project, even if the project theoretically complies with class A.
“Energy efficiency cannot be just theoretical – all solutions must be implemented in reality. Only then will the class be recognized,” says Laima Butkienė, head of the State Territorial Planning and Construction Inspection Department.
Need help?
If you are planning to build a Class A house or renovate an existing building, it is important to comply with all legal and technical requirements from the outset. From the preparation of documents to the actual construction, every decision has an impact on whether the building will meet the mandatory energy efficiency class.
The Stav.lt team can help you throughout the entire process: from preparing the design brief and calculating the energy efficiency of the building to working with certified assessors who will ensure that your building not only looks modern but also meets all the requirements for 2025.
Contact us if:
- you need advice on A or higher class requirements;
- you don’t know what documents are required in your specific case;
- you want to ensure that your project complies with current STR and energy efficiency regulations.
Stav.lt – when construction becomes simpler.