The energy performance requirements for newly constructed buildings

When we are preparing to build a new house, we look for the best solutions because we want the house to be energy and cost efficient. Many people call such a house an “energy efficient building”. This type of house is energy efficient due to a set of complex measures: a properly insulated building, the correct orientation of the building in relation to the countries of the world, renewable energy sources (solar energy, heat from the soil, heat emitted by lighting or household appliances).

Buildings (parts thereof) are classified into 9 classes according to energy efficiency: A++, A+, A, B, C, D, E, F, G. Energy performance certification of buildings is a process regulated by Lithuanian legal acts, during which the energy consumption of a building is calculated. The higher the energy class of the house, the lower the heating costs or they are almost zero. We would like to inform and remind you that from 2021, all new buildings (or parts thereof) throughout the European Union will have to meet the requirements for energy efficiency class A++. A+ ir A++ class houses are certified in Lithuania, at the Certification Center of Building Products.

Passive houses are also distinguished („Passivhaus“).These are houses with very low energy demand, because most of the heat demand is met by thermal energy from passive sources. The „Passivhaus“ certification process only takes place at the Passive House Institute in Germany.

Every house must have an official document – the house energy passport, which confirms that the house meets the energy efficiency class or the requirements for passive houses. But the most important value of such houses is measured by a comfortable microclimate and low heat consumption. Top quality windows also contribute to the good thermal insulation of these houses.



Windows are one of the many elements of a building. It is found that 35-40 per cent of the heat of a building is lost through leaky and poor quality windows. When granting an energy performance certificate, specific losses are also assessed, i. e. energy that we lose through partitions: through windows, doors, walls, ceilings, floors.

The main criterion for the energy efficiency of windows is the heat transfer coefficient (Uw), which is regulated by EU normative documents. Specific requirements for heat transfer coefficients of building windows are determined in the technical description of the building project, after the designer evaluates the influence of thermal insulation and all other factors on the general characteristics of the building. The same value of Uw for windows of the same area is determined worldwide.

The following are the minimum requirements for windows and doors:

Heat transfer. The heat transfer coefficient of windows and doors of an energy efficiency class A+ residential house should not exceed 0.85 W/(m2K); on the energy efficiency scale of windows, this would correspond to a rating of A+ to A;

Air permeability. Air permeability is an important criterion for buildings of energy efficiency classes A, A+ or A++. The higher the air pressure the window withstands, the higher class it is classified in.

Size and layout of windows in the building. Given the latitudes, it is advisable to install as many windows as possible on the south side due to natural sunlight, and large windows on the northern facades should be avoided.

The windows of a passive “house collect” solar energy, which heats the interior space. These are windows with a double-glazed unit, the glass of which is covered with a heat-reflecting coating. The heat transfer coefficient of such a double-glazed unit shall not exceed 0.75 W / m2K. In the manufacture of such windows, the space between the glasses is filled with a special gas, a special glass coating transmits short-wave sunlight, but protects against unnecessary long-wave infrared rays, thus ensuring optimal solar heat storage.

In many European countries, windows and doors are ranked according to the energy efficiency scale – the windows with the worst properties with Uw of 1.5 W/(m2K) and higher are classified as class G, and the most energy efficient windows with Uw up to 0.7 W/(m2K) are of the highest class – A++.

From 1 February 2019, new and reduced requirements for heat transfer coefficients of doors and windows of A+ and A++ residential buildings came into force. We present updated calculations of normative specific heat loss and energy efficiency indicators of partitions of buildings (parts thereof) of energy efficiency class A of the value of heat transfer coefficients U (A) (W / (m2 × K)) of building partitions:

Description of partitions









Partitions of heated premises adjacent to the ground




Floors above unheated basements and cellars





Windows, skylights, bay windows and other transparent partitions




Doors, gates





When choosing windows and doors, it is very important to pay attention to their energy efficiency, to focus on the heat transfer coefficient, because the lower this value, the more and more heat is retained. The windows and doors of the house are not only an accent that diversifies the exterior and interior of the building, but also an important part of the building that contributes greatly to heat retention, proper ventilation of the premises, sound insulation and burglary prevention.

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