>That would in turn mean that more space is needed to build a house with thicker walls than normal. Yep, and until (this is slowly changing nowadays) building

>That would in turn mean that more space is needed to build a house with thicker walls than normal. Yep, and until (this is slowly changing nowadays) building permits will depend on the external surface of the house or internal surface+half of the external walls (it depends on local building codes), having "better" homes even in the countryside may be problematic. A "raw earth" house typically has 1 m thick walls, to be compared to the 30-40 cm of houses built in the '60's up to - say - 2010 and the 50 maybe 60 cm of houses built more recently including the (stupid) external foam insulation, this difference in wall thickness is very relevant. So you have a building lot of 900 sqm (30x30), and according to local Laws you can build on it 20%, your allowed 180 sqm, that is roughly 14x13=182 sqm, has 2x(14+13)=54 m of external walls. 182-54x0.3=165.8 net inner (floor) surface <- old 182-54x0.5=155 net inner (floor) surface <- new/insulated with foam 182-54x1=128 net inner (floor) surface <- raw earth In a nutshell, you lose one or two rooms.