New CTE update: How does it affect the healthiness of buildings?

May 2020

On 20 December, the Council of Ministers approved RD 732/2019 , which amends the Technical Building Code. It is the latest update available, which was being begged for in the high energy efficiency sector. Since, with it, the energy efficiency requirements of the European Directive EU31/2010 on nearly zero-energy buildings are finally transposed (and almost at the last minute).

Its mandatory application was initially planned for 27 June 2020, but due to the state of alarm due to COVID19 , the duration in calendar days of the state of alarm is added to the initial date. This action of the CTE includes small changes to DB HE1 - Limitation of energy demand and establishes a new document, HS6 - Radon protection. These modifications will change the regulatory framework for energy efficiency and health.

DB HE1 - Limitation of energy demand

Apart from increasing the requirement to limit the thermal transmittance U (W/m2K) of each element of the thermal envelope, this regulatory change increases the requirement for air tightness and airtightness of openings.

This requirement is in line with optimising heat losses through the envelope. The air permeability of the envelope is regulated in section 3.1.3 and is divided into:

  1. The air permeability (Q100) of the openings according to table 3.1.3.a-HE1 and values of 9 or 28 m3/h.m2 according to climatic zones (class 2 and class 3 of UNE En 12207:2017).
  2. The air permeability of the building envelope for buildings with a total useful floor area of more than 120 m2, as a function of its compactness and the air change ratio for a differential pressure of 50 Pa (n50 - blowerdoor test).

The clear objective of increasing airtightness in buildings is the energy optimisation of the thermal envelope. The curious thing is that, as this requirement increases, since 2017 and following the update of DB-HS3 - Indoor Air Quality (Order FOM/588/2017) the ventilation flow rates required are increasingly lower.

In order to assess the effect of this ratio on the indoor healthiness of rooms, the minimum air exchange rates are calculated for dwellings with different numbers of bedrooms.

CTE update: How does it affect the healthiness of buildings?

So, if the minimum renovations/hour required for ventilation in living spaces have decreased, is the air renewal needed to remove indoor pollutants guaranteed?

Indoor air quality is essential for the comfort and well-being of building occupants. It is affected by various pollutants that may be derived from building materials and equipment, furnishings, cleaning products, or our daily activities. Therefore, ensuring adequate air renewal is essential to evacuate stale and polluted air and to introduce cleaner and fresher outside air.

HS6 - Radon protection

Finally, the update of the CTE also includes the incorporation of a new document on health. DB HS6 includes for the first time the risk of exposure to radon as a consequence of the transposition of Directive 2013/59/EURATOM, in municipalities where there is a risk of exposure.

Again, construction and finishing materials, as well as adequate air renewal, will be critical to avoid the risk of radon exposure.


Regulatory updates are necessary to ensure legislative support for building construction. However, regulatory support is only the starting point. Based on the analysis carried out, a reduction in energy demand, complemented by a reduction in airtightness, are essential for the energy optimisation of the building and to ensure minimum energy consumption.

However, a reduction of the ventilation flow rate in more airtight rooms, without proper planning of the air renewal system used, will not always ensure adequate indoor air quality.

It is therefore becoming increasingly important to implement air quality monitoring systems . continuous air quality monitoring and verification of the minimum necessary air flow. In order to meet the basic requirements of health and safety in terms of regulations and to provide adequate comfort and health for the users.

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