Population Equivalent: What Is a “PE/EH” and How To Size an Individual Sewage Treatment System?

Population Equivalent (PE) or Equivalent Habitant (EH) in French, is a unit of measurement defined in France by Article 5 of the Ministerial Decree of March 7, 2012, amending the order of September 7, 2009.

The sizing of an individual sewage treatment system is not based on the actual number of occupants of the house, but on its potential occupancy. The calculation rule retained is the following:

1 Population Equivalent = 1 Main Room, or 1 PE = 1 MR.

Article 5 of the Ministerial Decree of March 7, 2012, states:

“The sizing of the installation expressed in numbers of population equivalent is equal to the number of main rooms within the meaning of Article R. 111-1-1 of the Construction and Housing Code, with the exception of the following cases, for which a specific study must be carried out to justify the sizing bases:

• establishments receiving from the public, for which the sizing is carried out on the basis of the reception capacity;
• single-family dwellings where the number of main rooms is disproportionate to the number of occupants.”

Moreover, it is important to refer to this definition coming from the article R.111-1-1 of the Construction and Housing Code:

“a dwelling includes, on the one hand, main rooms intended for the stay or the sleep, possibly isolated rooms and, on the other hand, service rooms such as kitchens, shower rooms, toilets, laundries, storerooms, dryers, as well as, if necessary, clearings and dependence.”

However, this definition lacks precision: which “isolated rooms” should be considered as main rooms? Is an office with or without windows or a basement playroom a main room?

The only clear definition of a main room in the French legislation seems to be the “annex relating to the standards of the surface and habitability applicable to the residences having benefited for their acquisition or their construction as accession to the first property of refundable interest-free advances” one (no less!) of the “Decree n°2005-69 of January 31, 2005, relating to the refundable interest-free advances for the acquisition or the construction of residences in accession to the property and modifying the code of the construction and housing”. Note that it is also referred to in Annex A (“regulatory texts”) of XP DTU 64.1.

From § 2.1 “dimensional standards” and § 2.2 “opening and ventilation”, it can be deduced that a main room is a living or sleeping room (including offices, playrooms, etc.) with a ceiling height of at least 2.30 m and a surface area of at least 7 m2, with an opening (= an opening that allows light to pass through and allows ventilation) into the open air.

The population equivalent (PE) corresponds to the number of main rooms in a house.