# Usable building area

The building area is used in Germany as an energy reference area size for residential buildings in connection with the Energy Saving Ordinance. ${\ displaystyle A _ {\ mathrm {N}}}$

It is determined as follows:

${\ displaystyle A _ {\ mathrm {N}} = V _ {\ mathrm {e}} \ cdot 0 {,} 32 / \ mathrm {m}}$
${\ displaystyle V _ {\ mathrm {e}}}$(heated building volume) [m³] = volume that is enclosed by the heat-transferring area A (determined according to EnEV 2009 , Annex 1 No. 1.3.1).

If the floor height h g is less than 2.5 m or greater than 3 m, the usable area of the building must be calculated as follows:

${\ displaystyle A _ {\ mathrm {N}} = \ left ({\ frac {1} {h _ {\ mathrm {g}}}} - {\ frac {0 {,} 04} {\ mathrm {m}} } \ right) V _ {\ mathrm {e}}}$

## Energy reference areas in Switzerland and Austria

In Switzerland and Austria, the term energy reference area is used, which in residential buildings normally corresponds to the gross floor area ( including the surrounding walls). With storey heights of 3.125 meters, the usable building area is identical to the energy reference area on full storeys.