Old house, replacing floorboards laid on concrete

[Donkmeister]

My house was built in the years just after WW1. The ground floor is mostly a concrete slab, but in a couple of places I have found that they poured the concrete a little lower and inset wood directly into the concrete. Comparing notes with someone who has the same design of house, this is an original feature.

In the first place, there was bitumen coating the wood and no damp. However, lifting an old cheapo laminate floor today I have found that the wood is now soil with few signs it was ever wood.

Now... Doesn't help that the previous owners effectively sealed the damp in with the laminate, but what was the purpose of building this way?

My plan is to dig out the "soil" and use hardiboard onto the concrete to bring it to slab level and underlay/carpet on top. Am I saving up problems for a future owner?

It's just one room, the other rooms all have finished floors now as they had no issues.

 

[Donkmeister]

Update: the really soggy bit was only by the front door. Once I ripped up the rest of the laminate it was clearly suffering from lack of ventilation but wasn't actually wet or lacking structure. I've pulled it all out though so I can replace with insulation and concrete.

So my job is now to find the leak in the front door area, fix that, and raise the level of the concrete.