1. In housing buildings, the inhabitable spaces within them, the waste storage areas, the basements, parking zones and garages; and in buildings of any other use, the parking zones and garages, consider as valid the indoor air quality requirements established in Section HS 3 of the Technical Code of Building Construction.

2. The rest of buildings will have a ventilation system that will provide enough outdoor air flow to prevent, in the different premises in which any human activity is carried out, the formation of elevated concentrations of contaminants, in accordance with what is established in section and thereafter. In order to comply with this section the procedure established   in UNE-EN 13779 is considered to be valid.

Indoor air quality categories based on building use.

Depending on the building or premises use the indoor air quality category (IDA) that should be reached will be, as a minimum, the following:

  • IDA 1 (optimum quality air): hospitals, clinics, laboratories and nurseries.
  • IDA 2 (good quality air): offices, residences (communal zones in hotels and similar, residences for the elderly and students), reading rooms, museums, tribunals, classrooms and similar and swimming-pools.
  • IDA 3 (medium quality air): commercial buildings, cinemas, theatres, meeting rooms, hotel bedrooms and similar, restaurants, cafeterias, bars, dance halls, gymnasiums, sports premises (except pools) and computer rooms.
  • IDA 4 (low quality air)


Minimum flow for ventilation from outdoor air.

1. The minimum flow for ventilation from outdoor air, necessary in order to reach the indoor air quality categories indicated in section, are calculated in accordance with some of the following methods.

A. Indirect method of outdoor air flow per person.

a) the values in table will be used when the people have a metabolic activity of around 1,2 met, when the production of contaminant substances from human sources are low and when smoking is not allowed.

Table Outdoor air flow, in dm3/s per person

Category DM3/s per person
IDA 1 20
IDA 2 12,5
IDA 3 8
IDA 4 5

b) For premises where smoking is allowed the outdoor air flows will be, at least, double those indicted in table
c) When the premises has specific areas for smokers these must be premises that are closed off , air-tight and  sealed and sunk in relation to the adjoining premises.

B. Direct method of perceived air quality.

In this method based on the CR 1752 report (olfactory method), the values to be used are the ones in table

Table Quality of perceived air, in decipols.

Category dp
IDA 1 0,8
IDA 2 1,2
IDA 3 2,0
IDA 4 3,0

C. Direct method of  CO2 concentration

a) For premises with elevated metabolic activity (dance halls, sports and physical activity premises, etc.), in which smoking is not allowed, the CO2 concentration method could be used, a good indicator of human bio-effluent emissions. The values are indicated in table

Table CO2 concentration in premises

Category ppm(*)
IDA 1 350
IDA 2 500
IDA 3 800
IDA 4 1.200

(*) Concentration of CO2 (in parts per million in volume) above the concentration in the outdoor air.

b) For premises with an elevated production of contaminants (pools, restaurants, cafeterias, bars, some types of shops, etc.) the data in table could be used, although, if the composition and flow are known for the contaminating substances, the dilution method in section E is recommended.

D. Indirect method of air flow per surface unit.

For spaces that are not permanently occupied by human beings, the values in table be applied.

Table  Outdoor air flow per surface unit in premises that are not permanently occupied by human beings.

Category DM3/(s*m2)
IDA 1 no aplicable
IDA 2 0,83
IDA 3 0,55
IDA 4 0,28


E. Dilution method.

In premises where there are existing known emissions of specific contaminant materials, the dilution method is used. For these purposes the calculations carried out as indicated in section  of  EN 13779 are considered as valid. The concentration obtained for each contaminant substance, considering the concentration of SUP supply air and the emissions in the same premises, must be less than the limit set by the health authorities.

2. In climate controlled pools the ventilation from outdoor air necessary to dilute contaminants will be 2,5 dm3/s per square meter of water and beach surface area ( not including the spectator zone). To this flow we should add the necessary flow to control relative humidity, if required. The premises will be maintained at a negative pressure of between 20 to 40 Pa in relation to adjoining premises.

3. In hospital and clinic buildings the values in the UNE 100713 norm are valid.


Minimum outdoor air filtration for ventilation.

1. The outdoor air for ventilation will be duly filtered before entering the building.

2. The minimum filtration classes to be used, depending on the outdoor air quality (ODA) and the required indoor air quality (IDA), will be those indicated in table

3. The quality of outdoor air (ODA) will be classified according to the following levels:

  • ODA 1 : pure air that may contain solid particles (e.g. pollen) temporarily.
  • ODA 2 : air with high concentrations of particles.
  • ODA 3 : air with high concentrations of gaseous contaminants.
  • ODA 4 : air with high concentrations of gaseous contaminants and particles.
  • ODA 5 : air with very high concentrations of gaseous contaminants and particles.

Table Filtration classes

  IDA 1 IDA 2 IDA 3 IDA 4
ODA 1 F9 F8 F7 F6
ODA 2 F7/F9 F8 F7 F6
ODA 3 F7/F9 F6/F8 F6/F7 G4/F6
ODA 4 F7/F9 F6/F8 F6/F7 G4/F6
ODA 5 F6/GF/F9(*) F6/GF/F9(*) F6/F7 G4/F6

(*) The installation of a gas or chemical filter (GF) located between the two filtration stages must be foreseen.

4. Pre-filters will be used in order to keep the ventilation and air treatment unit components clean, and also to prolong the useful life of the final filters. The pre-filters will be installed at the outdoor air inlet to the treatment unit, as well as in the air-return inlet.

5. The final filters will be installed after the treatment section and, when the premises used are especially dirt-sensitive, after the supply air fan, making sure that the air distribution over filter section is uniform.

6. In all filtration sections, except those located at outdoor air inlets, the dry working conditions will be guaranteed; the relative air humidity will always be less than 90%.

7.The filter sections in class G4 or less for indoor air categories IDA 1, IDA 2 and IDA 3 will only be admitted as sections to those indicated in table

8. The heat recovery apparatus must always be protected with a class F6 or higher filter section.


Extraction air.

1. Depending on the building or premises use, extraction air is classified in the following categories:

a) AE 1 (low level of contamination): air from premises where the most important emissions of contaminants come from the construction and decoration materials, in addition to the people. This excludes air coming from premises where smoking is allowed.

b) AE 2 (moderate level of contamination): air from occupied premises with more contaminants than in the previous category, in which, moreover, smoking is allowed. Included in this section are: restaurants, hotel bedrooms, changing rooms, bars, warehouses.

c) AE 3 (high level of contamination): air coming from premises that produce chemical products, humidity, etc. Included in this section are: bathrooms, saunas, kitchens, chemical laboratories, smoking rooms.

d) AE 4 (very high level of contamination): air that contains odorous substances and contaminants that are a health hazard in concentrations greater than those allowed in the indoor air of the occupied zone.

Included in this section are:  extraction  from smoke extractors, parking zones, premises that handle paints and solvents, premises that keep dirty linen, premises that store food waste, premises for smokers in continuous use, chemical laboratories.

2. The air extraction flow for service premises will be at least 2 dm3/s per m2 of floor surface.

3. Only the air in category AE1, tobacco smoke free, can be returned to the premises.

4. The air in category AE 2 can only be used as transfer air from one premises towards service, bathroom and garage premises.

5. The air in categories AE 3 and AE4 cannot be used as recirculation or transfer air. Moreover, air expulsion from these categories towards the exterior cannot be jointly done with the air expulsion from categories AE 1and AE 2, in order to prevent possible cross-contamination.