EPBD 2024: what the new directive asks of the building envelope

What a directive is, and what a regulation is

A directive binds the member state, not the developer. Each member state must transpose it into national law, and the deadline was two years from entry into force, so May 2026. Since 1 January 2026, Croatia has had the Act on Energy Efficiency in Buildings (Zakon o energetskoj učinkovitosti u zgradarstvu, NN 155/25), which already transposes part of the directive. The limit values for design are still set out in the Croatian Technical Regulation on the Rational Use of Energy and Thermal Protection in Buildings; check its current version. The deadlines and principles in this article are taken from the directive.

Zero-emission buildings

The central concept is the zero-emission building (ZEB). It replaces the nearly zero-energy building. A ZEB has a very low energy demand, and covers what it does use from renewable sources on the building, from a renewable energy community or from a district heating and cooling network. It must not burn fossil fuels on site.

• New buildings owned by public bodies: ZEB from 1 January 2028.
• All new buildings: ZEB from 1 January 2030.

Each member state sets the maximum energy use for a ZEB to suit its own climate. For Croatia, we are still waiting for that figure.

Existing buildings

Minimum energy performance standards are being introduced for non-residential buildings. By 2030, each member state must renovate the worst-performing 16% of its non-residential stock, and by 2033 the worst 26%, measured by primary energy. For residential buildings there is no obligation per building, but a target for the stock average: average primary energy use in residential buildings must fall by 16% by 2030 and by 20–22% by 2035, with more than half of the saving coming from the worst-performing buildings. How this is shared out across buildings in Croatia will be decided by the national building renovation plan.

What else is coming

• An energy performance certificate on a common A–G scale across the Union, with G for the worst 15% of each member state’s stock.
• A building renovation passport: a step-by-step renovation plan, voluntary for the owner.
• Solar installations on new buildings, phased in from public and non-residential to residential, where technically and economically feasible.
• An end to subsidies for stand-alone fossil fuel boilers from 2025, with the aim of phasing fossil fuels out of heating entirely by 2040.
• A smart readiness indicator and electric vehicle charging infrastructure, depending on the size of the building.

Where glass comes in

The directive does not set Ug or g. It requires the building to be assessed as a whole, on primary energy, for both heating and cooling, and new buildings to be designed so that they do not overheat. That is where glass comes in, twice over.

In winter through Ug: the lower the Ug, the lower the heat loss. That is well known, and until now that is where it usually stopped. In summer through the g-value: the share of solar energy that passes through the glass. In the cooling demand calculation, the gain through a window is its area times g times the solar radiation on that orientation, reduced by any shading. On a building with large areas of glass facing south and west, that term quickly becomes the biggest item in the cooling calculation. Triple glazing reduces it only slightly: from 64 to 53%.

When the summer overheating check fails, the designer has three levers: less glass, external shading or a lower g. The first changes the architecture, the second adds cost and maintenance, the third is a change of coating in the same window. That is why g should be specified in the bill of quantities alongside Ug, not instead of it.

For the bill of quantities today: alongside Ug, specify g and light transmittance, by façade orientation. Eurostaklo calculates its insulating glass units with Guardian’s performance calculator, so the values in the quote match the technical data sheet and can go straight into the energy calculation.