So thermal bridges, yes, but not strong enough to cause mold?
The exterior walls are insulated on the side facing the soil, and even for them, with their (relatively to the interior walls) larger contact area, the lateral clearance is greater. The interior walls, with their smaller contact area, have hardly any relevance here.
I thought insulation under the base slab had long been standard. I was also concerned since it is a living basement and not a utility basement.
An extended scope of work increases value creation. A separately commissioned base slab contractor (someone only commissions them who tunes out my posts) will gladly sell you the insulation underneath. Integrated into the overall (shell) construction contract, "it stays in the family" whether the insulation is laid under or on the base slab, or in the case of individual contract awards, it tends to fall under the screed layer installer’s contract (at least never the civil engineer’s). From your point of view, it might come to the same thing, but the money flows from your pocket either way. However, every contractor wants it specifically to flow into their own pocket and is not guardian of their brother’s. So "standard" means "your money in my pocket, not in one of the other participants’." That is why I so strongly advise against consulting contractors about the most suitable measures when building in existing buildings: because everyone is eyeing their slice of the cake; and whether the client has to bake more cakes for the hunger of the other participants is of no concern to any contractor. I had already calculated this in the wondrously no longer findable post #28 of the thread :
... the absolute never-ever mistake is asking executing companies. They all only think about themselves and don’t care whether you have leftover incomplete items at the end of your budget. Get five of them, then one will consume 50% of your budget, one 40%, the other three will be able to calculate and understand that only 20% each can be for them but will tell you that then only the very minimum is possible. One thinks it should be at least half more, and the other two are even saying double. So you add up: 50 + 40 + 30 + 40 + 40 = a total of 200 percent of your budget and can come to only two conclusions. One, that you don’t have or don’t want to spend that much, and two, that "tear out and new" would already be cheaper. And these 200% are only cost estimates; the quotations are even higher, 230 percent, oh and VAT was not included, so 273.7 percent, and prices keep rising until execution, under 280% it won’t work.
A living basement will be included in a controlled residential ventilation system as today’s "standard" – this also addresses the mold risk.