Is insulation on 30cm concrete wall worth it?
Someone else can feel free to edit in the SI unit R and/or U (=1/R) values, I have a conversion stashed somewhere but it's not handy. Off the top of my head, in &quot;English&quot; units mostly only used on the USA now, 30cm (12&quot;) of concrete or stone is roughly R1 ([1 square foot•hour•°F difference]/BTU) while 2.5 (1&quot;) cm of foamboard is roughly R3.5-6.5 (depending on the foamboard type) and 2.5cm (1&quot;) of rockwool or cellulose is R3-3.3
So merely adding 2.5cm of insulation (not much at all) to the 30 cm of concrete would roughly quadruple (or better) the thermal resistance of the bare wall. Being only one room, and only the walls, it may not make much difference until you do more (the heat will leak elsewhere), but it will make a difference.