Residential buildings in Latvia are one of the essential heat consumers during the heating season. In 2008 the residential sector in Latvia has consumed 74% of all amount of produced heating energy. The majority of residential buildings were constructed within the period from 1965 to 1990. At this time mainly typical buildings were constructed. Types of buildings 103, 316 and 467 series were among the most widespread. There are approximately 38 933 multi apartment buildings in Latvia. The standard thermal conductivity for exterior brick walls was in average 1.33W/(m2•K) and for exterior expanded-clay concrete walls – 1.20W/(m2•K), which is at least 3.5 times higher than the values specified in the current Latvian Building Code LBN 002-01 “Thermal performance of building envelope” [3] which is valid in Latvia.. The largest part of residential buildings (89%) is privately owned, 11% belong to the state and self-governments and 2% belong to apartment cooperatives. The residential building stock of Latvia is represented mainly by one and two-room apartments.