Floorboards and damp proof

[sihackett29]

Some help needed please!
I have recently bought a 300 year old house in the UK that has a basement with a sump pump in and is obviously natural quite damp.
Above the basement there are floorboards with no damp proofing. I’ve just pulled up carpet in lunge and revealed the floorboards. Would we be ok sanding these down and varnishing them or do we need something between them and the basement? The dark boards on the photo attached are on a concrete base. The light ones are replacements and have a direct hole to the basement

 

[oldbutnotdead]

Thermal insulation would be good (unless you're going to heat the basement). Make sure there's good airflow in the basement (airbricks high in the walls near joist height would be favourite) and you'll be fine.

 

[sihackett29]

Thank you! Stupid question but would you just put thermal insulation below the boards in the middle section?

 

[oldbutnotdead]

Your 'boards on a concrete base'- if it's a suspended floor (gap between joists and subfloor) then yes insulate between joists under there. Or are the 'joists' actually battens sitting on the concrete- probably not much room to get any in there, you need to check that there's a DPM under that slab and you might find there's insulation under it anyway.