In article ,
The Natural Philosopher writes:

Returning to the original posters question, if the floor has underfloor
draughts, I would seal it with hardboard, and mastic around the
skirting, and assume a U value of about 5 for the wood floor, and then

When I moved in to a 1900 house 18 years ago, you could see where
the drafts came through the floor as it had left a dirty mark on
the carpet. In this case, it was all round the edge of the room
where there was a 1/4" gap between the bottom of the skirting and
the floorboards. After that carpet had been ripped out, I repainted
the skirting, and deliberately spilled over 2" onto the floorboards
too. When the paint was dry, I bought a very wide roll of good
quality sellotape, and stuck it carefully along the gap between the
skirting and the floor, rising to about 20mm above the floor so it
would be hidden by the new carpet which was subsequently installed.
18 years on, that's still doing fine and has to this day stopped any
draft coming up through the edge of the carpet, at least to the
extent that there is no discolouration caused by the carpet filtering
dust out as the previous carpet had done.

--
Andrew Gabriel