DB-HE: energy saving in the Spanish building code

Section	Requirement	Object
HE 0	Limitation of energy consumption	Ceiling on total and non-renewable primary energy consumption
HE 1	Conditions for demand control	Envelope quality: U-values, thermal bridges, airtightness, solar control
HE 2	Thermal installations	Refers to the RITE, the Spanish HVAC regulation
HE 3	Lighting installations	Efficiency and control of lighting in non-residential uses
HE 4	Renewable contribution for hot water	Minimum renewable coverage of domestic hot water demand
HE 5	Renewable electricity generation	Minimum power in certain buildings

Three articles develop this branch: the consumption and demand limits of HE 0 and HE 1, the practical definition of the nearly zero-energy building, and the renewable contributions of HE 4 and HE 5. All three rest on the same energy verification of the building.

Every quantified DB-HE requirement is modulated by the climate zone, identified by a winter severity letter and a summer severity number derived from the locality and altitude, and by the building's use. The same design can comply on a temperate coast and fail on the cold plateau without changing a single drawing: this is why the energy check must be run with the real site data from the very first iteration.

Verification is carried out with recognised calculation tools, HULC being the official reference tool. The result is not a formality: the consumption and demand indicators produced by the verification are the ones the justification report incorporates and the ones checked at permit stage.

The DB-HE governs the largest regulatory cost block of the CTE. In the envelope: insulation thicknesses and grades in façades, roofs and floors, thermal bridge treatment, window and door joinery with its U-values and solar factors, airtightness. In the systems: efficient generation, with air-to-water heat pumps as the current market's dominant solution, ventilation coordinated with DB-HS 3, and the renewable systems of HE 4 and HE 5 where applicable.

As an indicative order of magnitude, the thermal envelope and joinery represent between 15 and 25 % of the PEM (presupuesto de ejecución material, the direct construction cost) in new multi-family residential. It is also the block where the CTE's performance-based approach offers the greatest optimisation margin: different combinations of insulation, joinery and generation achieve the same compliance at noticeably different costs, and that trade-off deserves to be made with figures on the table.

It is also worth looking ahead: the pending CTE reform, transposing the European directive on the energy performance of buildings, reinforces this branch with the zero-emission building concept and the extension of renewable generation requirements. Long-horizon feasibility studies should already factor in that tightening direction.

The first is verifying late: a last-minute energy check turns any deviation into extra cost, because the cheap levers, such as compactness or orientation, are no longer available. Energy verification belongs to preliminary design rather than to the detailed design.

The second is forgetting thermal bridges: in well-insulated envelopes, poorly resolved junctions concentrate a disproportionate share of losses and condensation pathologies. They are resolved in the construction detail, not in the insulation thickness.

The third is specifying joinery by U-value alone, ignoring the solar factor and airtightness, which are part of the same verification. The three parameters are specified together and checked on site.

The fourth is treating HE and HS as separate worlds: the ventilation required for indoor air quality is one of the largest energy demand items, and heat recovery solutions are justified precisely at that crossroads. Both documents are verified against the same ventilation flow rate.