Historic buildings, as well as much newer ones, with architecturally attractive facades, will not be thermomodernized from the outside, Because of their high value stands in the way. One such case is mentioned in this article, in which an analysis of external vertical partitions was carried out, in terms of heat and humidity in a small residential building located in southern Poland and built in 1930. The article describes a hygrothermal analysis of the above mentioned partitions, before and after thermomodernization, which should assess the legitimacy and effectiveness of using controversial methods of insulation of external building partitions from their internal sides. The article is a summary of a five-year observation and research of the object, after its thermomodernization in 2015. The analysis was focused on its vertical partitions.