Insulation for a cold drafty boarded floor

If it's really that bad.......I'd go for the plastic backed stuff on a roll, tucked under skirting if poss, AND the green boards on top.

 

I would have laid a minmum of 100mm Kingspan or similar rigid insulation between the joists supported on tile batten & foamed any remaining gaps before boarding the floor.
Not fan of Scotia edge strips, prefer to remove the skirting, looks neater when finished in my opinion.

Just doing the dining room here with laminate, been using 'Sonic Gold' underlay, as a built in foil dpm, & has a generous 200mm Joint overlap, but you must tape the joints. I ran the underlay joint overlap about 25-30mm up the walls, held in place with a minute spot of gripfill until I fitted skirtings using gripfill..

 

What sort of crawl space is there, I done jobs, where I've been able to raise a few boards to gain access, & then fit rigid insulation with out lifting the whole floor.

 

Send the lady of the house down there.

 

I don't know what the 'plastic backed stuff' is, unless it's the very thin foamy stuff I've seen sold in some places as underlay - but it's only around 2-3mm thick, and tears really easily.

I've used the ~8mm thick green fibre boards myself for exactly this job in my hallway - it needed new floorboards anyway. Cut to fit tightly against the wall under the skirting, and all join cuts landing on joists. Sealant (I just used really cheap 'frame' sealant) along the wall and between the sheets to make it as draught proof as possible.

As it was a narrow hallway, I just glued the T&G and floated it on top, held down by new skirtings.

That seemed to have worked.

Obviously your floor will need fixing down, but you have an existing floor to work on.

Trying to get Kingspan or similar under the floor is crazy, in my view. LOTS of work and expense for very little gain. The floor is the least important surface to insulate (unless it happens to be a solid concrete lump...). And anything you add to it will make a huge difference.

For floorboarded floors, stopping draughts is the biggie.

Urban will not only have this fibre board, but also the existing T&G - which is a cracking insulator in itself. Adding anything else to that lot will make very little difference to the insulation value of the whole room.